New video of Halema'uma'u Crater; and a great roll cloud in Tennessee

There is a 4-minute long UAS (Unoccupied Aircraft Systems) video released by the USGS today showing the enormous collapse features around the rim of Halema'uma'u crater. Filming was done two days ago on July 24. The trailer at the end of the video (which flashes by before you can read it!) says that the two flat surfaces that have subsided are the former caldera floor and the former floor of Halema'uma'u.
   

Photo as credited in text.

      On another topic, Colby Hutton of Adamsville, Tennessee took the adjacent photo of a roll cloud in Tennessee after a thunderstorm. A roll cloud is a subclass of "arcus clouds," low horizontal clouds (the other main type is a shelf cloud).  Roll clouds, according to Wiki, form along the leading edge of thunderstorm outflow where cold outrushing air lifts warmer air up to a level where condensation occurs, giving rise to the cloud. The most famous occurrences of roll clouds are the so-called Morning Glory clouds that form in Queensland, typically in September and October. These clouds form where air temperature reverses from its normal state (warm air at the bottom of the atmosphere, cooling upward), resulting in warm air on top of cool air. Shear across the inversion point (where the gradient changes) sets up the rolling motion, giving rise to the roll cloud.  They can last for several hours, be several hundred kilometers in length, and occur in sets. Conditions for the inversion are most likely to happen in the morning and hence the name "Morning Glory" in Queensland. They are not common--conditions for their formation are common in the spring in the midwest, but I lived there for 10 years and never saw one.  If there is too much moisture around, as in a thunderstorm, any roll cloud may be hidden amongst other clouds. Here's a link to a National Geographic short video of a roll cloud in Texas, and here's another spectacular compilation, not sure where it is from.

What in the world is "geofoam?"

In the past week, I have traveled the 135 mile route between Seattle and Vancouver, B.C. twice, each trip taking more than 6 hours when going north.  A significant part of the problem is waiting at immigration at the border, but an equally significant problem is the crazy highway maze from the border into Vancouver: continuous spots of merging 3,4,5,6 lanes down to 1,2 or 3.  Amidst the frustration, my suppressed desire to become a highway engineer emerged: either to design the interchanges properly using fluid mechanics principals, or to design them to punish the many drivers who skirt to the right-hand side "truck only" or "exit for duty-free" places to cheat and move way up in line.
     With this recent thinking about traffic engineering, I was interested today in an article on the WSDOT blog site regarding "geofoam" which I had never heard of. It is used in place of dirt because the use of real dirt takes longer and has higher costs. Dirt has to settle, and crews have to wait until the ground has settled before building a structure on top of it. The use of geofoam also reduces the weight on underlying soils: blocks of geofoam are placed on a section of ground that is greater than the weight of the geofoam. The blocks are glued together with a quick-setting roofing adhesive and then secured to the ramp walls with reinforcing steel. Ready now for concrete to be poured on top!
     So, what is geofoam? Does it have anything to do with "geo"? Not as far as I can tell, though it's probably more stable than the "ghost poop" foam beads that are used to cushion materials in packaging! It is "expanded polystyrene" manufactured into large lightweight blocks. I couldn't find a list of the elements/compounds in it, but according to one site, it is a "closed-cell, strong, but lightweight premium quality expanded polystyrene (EPS) foam." It is used in a variety of "residential, commercial, and industrial applications." Polystyrene has the general chemical formula (C8H8)n with a density of  1%-2% of that of soil of equal strength. 
     Geofoam is used because, for engineers, it has predictable properties compared to soil fills. It is basically (but not completely, see below) inert so that it won't spread into surrounding soils, e.g., lawns, gardens, farmlands...  It can even be installed by hand and does not require heavy machinery for installation.  It's quick and easy to install and can be installed in any type of weather and night or day, i.e., cheaper installation costs.  It can be dug up and reused.
     On the other hand, there are some serious disadvantages: It is a fire hazard if untreated.  It is soluble in petroleum solvents, eek.....if it comes into contact with a 'petroleum solvent' it turns into a "glue-type substance unable to support any load." Engineers have to figure out buoyancy problems because of it's low density: cars were crushed against a ceiling in one instance after floodwaters below a carpark floated it.  It is susceptible to insect infestations when used in buildings.
    Conclusion: The "geo" in geofoam has nothing to geology!

A brief history of explosive eruptions at Kilauea: 1790 and 1924 and a great 1955 video

First, kudos to the staff of Hawaii Volcano Observatory and the civil defense officials in Hawaii for the work that they are doing to keep people safe around Kilauea!

from: https://pubs.usgs.gov/fs/fs132-98/

Today (Wednesday, May 9) the USGS Hawaii Volcano Observatory put out a warning that the "steady lowering of the lava lake in "Overlook crater" within Halema'uma'u at the summit of Kilauea Volcano has raised the potential for explosive eruptions in the coming weeks." As of this announcement, the lava lake surface has dropped more than 200 m, and was subsiding at a rate of about 2 meters per hour. The water table currently lies about 520 m below the rim of Halema'uma'u. While 320 m seems like a long way to go to the water table, the USGS  says that since the early 1820's the floor of the summit crater has dropped to within 90 m of the water table at least three times.
        The fear is that the column of lava feeding that system might drop below the groundwater level and allow water into the conduit (illustrated schematically to the left). Interaction of the water with lava would result in steam-driven explosions, expelling debris around the Kilauea summit.  The notice issued by the USGS goes on to warn that in such explosions, ballistic blocks up to 2 meters across could be thrown in all directions for distances up to or exceeding 1 km. Such blocks could weigh "a few kilograms to several tons." Smaller rocks could go several miles and would be more likely to land downwind.

from U.S. National Register of Historic places

     The technical term for the process that might happen is "autocatalysis," although this term has a slightly different meaning in volcanology than in chemistry.  When magma is intruded into water, a thin cooled skin develops at the contact between the two substances. Such a skin allows magma to flow underwater without exploding because the red hot lava is prevented from contact with the water. However, if the skin is ruptured, water comes in contact with the lava and an explosion results. The explosion results in exposure of more lava to water, and so the feedback keeps the reaction going until either the water or the lava are exhausted.
     There are two known examples of such explosive eruptions at Kilauea. In1790, people were trapped  in the Ka'u Desert in what is now Hawaii Volcanoes National Park and left footprints in fresh volcanic ash that are now visited by tourists. Although legend has it that the footprints were from two parties of warriors, but research has suggested that the area was commonly used for hundreds of years (perhaps for obtaining sharp glass to use as tools) and that many of the footprints were made by women and children.
     The Hawaii Volcano Observatory was established in 1912, and in 1917, the great volcanologist, Thomas Jagger, studied Kilauea and published a major paper "Volcanologic Investigations at Kilauea" in the American Journal of Science (v. 43 (261) 161-220.) Jagger founded and remained Director of HVO until 1940. In 1924, only about 6 months after the eruption ended, he and R.H. Finch published a paper describing the second example of explosive eruptions at Kilauea, the events from February through May of that year (AJS, 8(47), 353-374, 1924). In January of that year, the lava lake in Halemaumau was fountaining and was 105 feet below the rim. In February, this subsided to 370 feet, but was relatively quiet except for numerous earthquakes on the Puna rift east of the summit, the location of current activity. The rift had vented lava in 1922 and 1923 and the possibility of further activity was openly discussed. In early April, a strong earthquake jolted Hilo, but no new cracks were observed in the ground. Earthquakes continued on the east rift zone, and after numerous earthquakes on April 21, fissures opened in the Kapoho district on April 23. Chasms developed in numerous places, some being as much as 3 feet wide. However, earthquakes diminished through the end of April.
     By May 6, the floor of Halemaumau was more than 600 feet below the rim, the actual depth not known because of avalanching material. Although the subsidence of the floor indicated lava draining from the summit, no lava flows were reported anywhere.  On May 11, for the first time since 1790, broken rocks were hurled from Halemaumau. Five explosions were reported on May 13, with one 400 pound rock being thrown 200 feet from the pit. Another explosion that day sent rocks a half mile into the air, some weightn hundreds of pounds.
    

8-ton boulder ejected May 18th, 1924, to 3500 feet from center of crater

May 18 (the date on which Mount St. Helens erupted in1980) marked the maximum of explosive activity in this sequence. One man who ventured too close to the pit died the day after his leg was crushed by ejected stones. Jagger describes "Heavy electrical storms accompanied by pisolitic mud rains followed the larger explosions. Brilliant lightnings shot through the califlower ash clouds. A marked air concussion was felt before the larger explosions." Continuous avalanching filled the air with dust and mud. Jagger took the continous explosive activity to indicate that the volcano was trying to clear a clogged throat as pressure repeatedly built up due to the debris in the conduit. He noted that the rocks ejected were not fresh lava nor were they bombs encased in lava. They were "olivine rock or gabbro...and old lava from the walls of the pit."
     The last notable explosion of the 1924 sequence was on May 24 with the ejection of rocks to 3000 feet, acconpanied by lightning and cracks of thunder, trembling ground, and a heavy deposit of ash.  Within 20 minutes, the eruption was over. The pit had enlarged to 3400 feet by 3000 feet in area, and to a depth of 1330 feet. By the end of June, seismicity had returned to normal levels.

P.S. Just discovered a nice USGS video of the 1955 east rift eruption. Could provide a good image of how the flank eruption (not the summit eruption) might proceed. And, a fun historic perspective on the technology of film making/sound track in those days!
 

Freak thunderstorms in India move along a trough

From the Hindustan Times, May 3, 2018.

It is probably well known by atmospheric scientists, but I had never stumbled across a chain of thunderstorms before! 
      Duststorms yesterday killed about 100 people and injured 200 more in the past day. They occurred in the provinces of Uttar Pradesh and Rajasthan in the north and northwest parts of India. The city of Agra, home of the Taj Mahal was particularly hard hit, with 36 deaths and wind speeds reaching 130 km/hour (80 mph). he Taj Mahal itself seems to have been undamaged.   Deaths seem to be due to collapsing trees and infrastructure. It is six weeks until the monsoon season and so dust is in plentiful supply. Traffic was snarled in Dehli by the dust and fifteen flights had to be diverted. In the city of Alwar, more than 100 trees were uprooted, falling on vehicles and electricity cables.

Dust storm approached Bikaner on Wednesday from here.

     According to the Hindustan Times, thunderstorms are common before the monsoon season develops, but the severity of this storm resulted from the collision of a number of factors.  To the west, Rajasthan has experienced unusually high temperatures. This condition aids moisture retention in the atmosphere and leads to the formation of larger clouds which increase the intensity of thunderstorms. To the north a low-pressure system called the Western Disturbance, carries in moisture from Eurasian water bodies which also fed into the thunderstorm system while a cyclonic circulation system over Haryana
triggered upward movement of the moisture laden warm air north of Rajasthan.  Referring to the lower blue panel in the graphic shown here, the motion of upwelling moist air feeds the thunderstorm clouds. When the clouds can not absorb all of the moisture, it rains and a downdraft forms.  When this downdraft occurs away from the updraft because of wind shear, it can create another thunderstorm, perhaps more than one.  The track of this chain from northwest to east (dashed line in the graphic) creates an extended low-pressure area along which the thunderstorms track.  The maximum impact was near the first thunderstorm in the Uttar Pradesh and Rajasthan region.
     In an apparently unrelated storm reported by Time.com, the southern east coast state of Andhra Pradesh had 36, 749 lightning strikes in 36 hours on Tuesday, with the loss of 9 lives. Last year, for comparison, there were about 30,000 lightning strikes over the entire month of May. More than 2000 people per year are killed by lightning strikes in India (compared to the U.S. where it is ~27/year).
     

The mysterious grooves on Barcena volcano

Furrows on the flank of Barcena filmed Sept. 12, 1952.

Barcena volcano was born on August 1, 1952, on Isla San Benedicto, located about 300 nautical miles off the west coast of Mexico and over 8 months a cone was built and its exterior became furrowed with a fairly unique set of furrows (grooves) (Richards, 1959). The process that created the furrows is still not understood. I review here the history of the eruption and in a later post, I will review speculations on the origin of the furrows.

Very few volcanoes have been observed from birth through growth, with Paricutin, Mexico, being the best documented because it was on land.  Barcena was visited only briefly during the 8 months of its growth. It was initially studied by Robert Dietz, who later became famous for his pioneering works on both meteorite impacts and sea floor spreading. Dietz (1914-1995) was searching some Navy records for sounds coming from Barcena. He didn't find them but, instead, found explosions arriving from Myojin Reef volcano which he was able to show had blown up and sunk a ship taking all 31 hands aboard to their death. According to Richards (p. 87) volcanologists appeared unaware of this eruption, and Dietz only became aware of it on August 27 when he read about it in the Los Angeles Examiner.  Dietz was on two airplane flights (Sept. 12 and 20) over the volcano, but apparently never wrote up his observations, at least in easily accessible literature. (Richards, p. 89) says that Dietz interviewed the pilot who visited on August 12 (see photo below of density current) and compiled a "mimeographed report". The pilot took two 16 mm Kodachrome motion picture films which Richards used for his documentation. The visit of this clipper (the M/V Intrepid) and its plane is the only source of information on Barcena between August 5 and Sept. 12.

Our knowledge of the events at Barcena stems almost solely from a paper** by Adrian F. Richards of the U.S. Navy Hydrographic Office, although two famous geologists, Dietz and Howel Williams (volcanology) both observed the island from two airplane overflights. Williams made a geologic sketch map of Isle San Benedicto from the plane observations and later wrote a brief statement published in something called "Volcano Letter" which we are trying to get hold of at the moment. The Richards paper is part of his 1957 Ph. D. dissertation at UCLA. In it, he says (p. 77) "The majority of the observations......during the period of cone building and lava extrusion were by the men of the California tuna fishing fleet." Specifically, and importantly for the question of when the furrows in the photo shown were formed, three men from the tuna fleet visited on August 1, 1952 on a clipper, two others on August 12 on a different clipper and its seaplane, and three others, including Dietz, on September 12 on a U.S. Air Force B29, 55th Strategic Reconnaissance Squadron.

This photo was taken on August 12 by T. Howell from seaplane.

The eruption began about 0745 on August 1, 1952 with a brief thin pencil-like column of steam ;  After a few minutes, this steam column dissipated and a dark gray-black column of ash and steam "shot skyward." This eruption cloud almost immediately began to spread laterally at the base.

Richards sorted through various eyewitness reports and speculations and concluded, along with Williams, that most of the new cone was built to an altitude of 1000' in the first few weeks (p. 92). Richards (p. 89, Table 2) pointed out that "the most striking feature of the initial eruptions" was the fact that the horizontal spread of the eruption column was much more rapid than its vertical rise, and he concluded that it "resembled the base surge of an atomic explosion." At one point (time is not well documented in Richards paper), the altitude of the plume was about 4500 feet and the "maximum lateral extent" (diameter) at the same time was about 11,000', so that the width/height ratio of the plume was 2.7.

Richards considered four possible processes for creating the grooves. He eliminated rain erosion because the furrows did not show dendritic geomorphology; avalanches of bombs because at Paricutin furrows created by bombs were curved, rather than straight and no bombs were found at the base of Barcena; and ash landslides because the furrows originate too far up on the rim for such a process to have occurred.  He settled on tephra avalanches or, here, density currents.

On August 12, a density current was photographed (the image shown here is an "unretouched enlargement from a 16 mm duplicate Kodachrome motion picture frame.") Unfortunately no scale is given for the photo, and the only identifiable feature is the crater rim in the upper middle left of the frame. From the motion pictures, Richards stated the following: the tephra avalanche appeared to have a rolling rather than a sliding motion. Bbut what does that mean? It's not a description commonly used in modern volcanology literature. Like other avalanches that he observed at Barcena, the tephra avalanche appeared to issue from the lowest point in the crater rim, and Richards states that "there appeared to be a gaseous dilation from the center of the avalanche." I take the latter to mean that it did not act like an incompressible gravity current, but expanded both vertically and laterally due to gas pressure.  There was, unfortunately, not enough resolution in the films to tell whether this avalanche furrowed the cone. During the time that it was spilling from the crater, a vulcanian column of dark ash and gas rose skyward. Slight changes in slope caused "pronounced differences in the behavior of the avalanches."

What was the role of tephra avalanches in building the cone versus eroding the furrows? In Richards summary of the "envisioned activity" (p. 112), he indirectly addresses this question. He concluded that the cone grew rapidly (i.e., over several weeks in early August) by "tephra fallout from the eruptions and deposition from the tephra avalanches." Then, between mid-August and September 12 when it was not observed, the violent phase of cone formation tapered, and tephra avalanches became intermittent. However strong, vertical vulcanian eruptions continued through this period.  By September, he says, they probably "slid and eroded" instead of being "rolling" and "caused the formation of the furrows.

Richards description does not allow us to state whether one tephra avalanche event could account for all the furrows, or if there were multiple events. We know, from observation of furrows created by the lateral blast at Mount St. Helens that a single event with a duration of probably only tens of seconds can erode furrows of comparable or even larger scale. Probably the only conclusion that we can draw from Richards accounts and reasoning is that the furrows were carved by one or more tephra avalanches.   

** Richards, A. F. (1959), Geology of the Islas Revillagigedo, Mexico. 1, Birth and development of Volcan Barcena, Isla San Benedicto, Bulletin of Volcanology, 22, 73-123.

Global Warming and Hurricanes

In the recent press coverage of hurricanes in the Caribbean, the question of the relationship of intensity and frequency of hurricanes to global warming has arisen many times. I'd like to summarize here the conclusions (as of Aug. 30, 2017) presented by the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration (NOAA). The material below is a direct quote, and the full report can be found here.

"Two frequently asked questions on global warming and hurricanes are the following:

• Have humans already caused a detectable increase in Atlantic hurricane activity or global tropical cyclone activity?
• What changes in hurricane activity are expected for the late 21st century, given the pronounced global warming scenarios from current IPCC models?

In this review, we address these questions in the context of published research findings. We will first present the main conclusions and then follow with some background discussion of the research that leads to these conclusions. The main conclusions are:

• It is premature to conclude that human activities–and particularly greenhouse gas emissions that cause global warming–have already had a detectable impact on Atlantic hurricane or global tropical cyclone activity. That said, human activities may have already caused changes that are not yet detectable due to the small magnitude of the changes or observational limitations, or are not yet confidently modeled (e.g., aerosol effects on regional climate).
• Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones globally to be more intense on average (by 2 to 11% according to model projections for an IPCC A1B scenario). This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size.
• There are better than even odds that anthropogenic warming over the next century will lead to an increase in the occurrence of very intense tropical cyclone in some basins–an increase that would be substantially larger in percentage terms than the 2-11% increase in the average storm intensity. This increase in intense storm occurrence is projected despite a likely decrease (or little change) in the global numbers of all tropical cyclones.
• Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones to have substantially higher rainfall rates than present-day ones, with a model-projected increase of about 10-15% for rainfall rates averaged within about 100 km of the storm center."

That is, storms are going to get more intense, and the frequency of very intense storms will increase.

Hurricane Irma strips the Virgin Islands

Of all of the press images showing local damage (toppled trees, destroyed buildings, cars and boats), this NASA before and after comparison of the Virgin Islands seems the most powerful. The diagonal distance is approximately 40 miles.

September 6, Major X-Class Solar Flare!!!

Spaceweather.com just announced that a coronal mass ejection (CME) got launched toward earth out of sunspot AR2673 at 1292 UT today, and unleashed a major X9.3 class solar flare--the strongest solar flare in more than a decade!! It caused a strong shortwave radio blackout over a large region (see figure).Analyists are still working on determining whether or not it is Earth-directed.  In a list of the most powerful solar flares recorded since 1976, this flare ranks at #14.  Compared to the Carrington Event of 1859, this event is relatively mild.  However there may be some fantastic auroras this week.  Go to spaceweather.com for updates.

The "natural gas for clean energy" flaw

(If this contains garbage in the last paragraph, please note that I have tried to correct it and can't seem to do it in Blogger.)


Bill McKibben has an interesting op-ed in The Seattle Times today debunking the argument that switching from coal to natural gas will "save the planet."  The argument goes like this: Replacing coal with natural gas does indeed cut down CO2 emissions, and this has been observed to happen as America's power plants have replaced coal with natural gas.  However, natural gas is methane, CH4 and it is 80 times more powerful at trapping heat in the atmosphere on a molecule by molecule basis.  Methane leaks during the drilling process and, McKibben asserts, if as little as 3% of natural gas leaks during fracking then it is WORSE for the atmosphere than coal.
      For perspective, the methane budget in the atmosphere is complicated because there are both natural and human sources. Natural sources include wetlands, termites, and oceans. Human-related sources include fossil fuels, livestock farming, landfills, biomass burning, rice agriculture and biofuels. The attached figure (from Bousquet, P. et al. Nature 443(7110), pp. 439-443, 2006) illustrates details.

From this reference based on the Bousquet article cited in the text.

     A 2016 paper by Turner et al. in Geophysical Research Letters (DOI 10.1002/2016GL067987) examined methane emissions over a ~ a decade (2002-2014) from satellite data and surface observations. They found that global emissions increased by 17-22 Tg/a and that the U.S. methane emissions accounted for  30-60% of this increase. The emissions were primarily in the central part of the country but could not be attributed to definite sources, e.g., relative amounts from livestock and oil and gas sectors. McKibben's argument appears to be based on the 30% number and thus is probably conservative.
     Leakage rates may be higher than 3%: An aerial survey of a natural gas and oil production field in Uintah County, Utah on one day found emission rates between 6.2-11.7% of average hourly natural gas production for the month of February. Obviously more data are needed but rates are clearly above 3% in this case. The authors (Karion et al., JGR, doi: 10.1002/grl.50811) stated that "this high leak rate probably negates any immediate climate benefits of using natural gas instead of coal or oil and represents a possible air pollution hazard."
    On the other hand, some studies point to lower leakage rates, e.g., Peischl et al. (JGR, doi:10.1002/2014JD022697) found leak rates from <1 1.5="" 10.1002="" 2.1="" 6.3="" a="" agency="" al.="" and="" are="" be="" between="" ch4="" doi:="" emission="" environmental="" et="" fayetteville="" found="" from="" haynesville="" higher="" in="" inventory.="" leak="" marcellus="" northeastern="" northern="" of="" p="" pennsylvania="" protection="" rates="" regions.="" ren="" shale="" significantly="" southwestern="" study="" than="" the="" these="" to="" u.s.="" virginia="" west="">less than 1 percent to over 6 percent.  It is possible that because of the reduction of coal and increase in natural gas use that the U.S. greenhouse gas emissions may have actually gone up during the Obama years. McKibben points out that "at least the Obama administration required drillers to keep track of how much methane they were leaking--one of the first acts of the Trump EPA was to scrap that requirement, apparently on the grounds that what you don't know can't hurt you." He then argues that the illusion that we are doing something to reduce climate change by switching to natural gas is hurting us because it is making it harder and slower to switch to solar power which emits no carbon at all (I guess that's if you don't count the fact that it probably takes carbon to produce solar panels at the this time.)

Another solar flare and coronal mass ejection, possible G2 event

Regions affected by blackouts from the July 14 solar flare

Update on July 15: Spaceweather.comsays that this will be a G2-class storm with possible intensification to a G3-class. G2=high-latitude power systems may experience voltage alarms, long-duration storms may cause transformer damage. G3 false alamrs triggered on some protection devices. Surface charging on satellite components, drag increase on low-Earth-orbit satellites. Radio navigation problems may occur. Aurora has been seen as low as Illinois and Oregon.

We are supposedly heading toward a sunspot minimum in 2019 or 2020, and this current solar cycle is the weakest cycle in more than a century. However, this morning there was an M2 solar flare and coronal mass ejection (CME) that may lead to a geomagnetic storm on July 16, 17. An M2 flare is "medium" sized (M) and of intensity 2 out of 9 possible levels. Peak fluxes for M flares range from E-05 to E-04 Watts per square meter at wavelengths between 1 and 8 Angstroms. This event happened in a sunspot AR2665 that had been quiet since it rotated onto the earth-facing part of the sun about July 7. It is the largest sunspot this year, more than 120,000 km across, about the same size as the planet jupiter. It had an "unstable beta-gamma magnetic field that indicated it contained energy for an M level explosion ( https://roslistonastronomy.uk/sunspot-ar-2665). According to spaceweather.com, the eruption lasted more than two hours and produced a "sustained fusilade of X-rays and energetic protons. Shortwave radio blackouts were observed over Asia and around the Arctic Circle, shown on the image above.

There is a video of the CME here:

http://spaceweather.com/images2017/14jul17/cme_c3_anim.gif?PHPSESSID=l96b1kdbcjp7fnr92iid0fkns4

The expanding cloud from the CME is expected to reach earth on July 16th and may spark geomagnetic storms and high-latitude auroras. Pray for clear weather in Seattle!

New coronal hole in the solar atmosphere, alert for aurora possibilities

Just saw a notice on Spaceweather.com that a large hole in the solar atmosphere is turning toward Earth. It is expected to blast us with a very high-velocity (700 km/second!!) stream of solar wind, arriving on June 16th, and possibly sparking G1-class geomagnetic storms. Could be interesting auroras particularly in the southern hemisphere because of the autumn darkness.

Spectacular video of a 400' wide waterfall in the Antarctic

There is a very well-written summary of two new papers in Nature in this weather.com article. Take a look at the video of the meltwater pouring off the surface of the ice sheet over a 400' wide waterfall. Scary!

Planet Jupiter Opposition from sunset April 7 to sunrise on April 8, 2017

(No, there is not a video link to the left, but read on and you'll get one.) The following from NASA press release.

Tomorrow night, Jupiter makes its closest approach to Earth in 2017 so it'll be big and bright. This only happens every 13 months, and you can spend all night watching it, weather permitting. Opposition means that Jupiter will be opposite the sun so, as the sun sets in the west, Jupiter rises in the east. It'll be straight overhead at midnight, and will be near Spica, the brightest star in the constellation Virgo. And, if it's cloudy you can still catch nearly the same view for nearly a month after opposition.

So, what are those stripes across Jupiter? They are ammonia  (NH3) clouds in its upper atmosphere bounded by powerful winds like our own terrestrial jet stream. The dark bands are called "belts" and the light ones are called "zones." Gas rises in the light bands, and sinks down in the dark bands. The colors arise from slightly different temperatures and chemicals in the bands. Adjacent bands have winds in opposite directions. There is quite a bit of uncertainty about what actually gives the bands their colors (blue, orange, brown bands, and the "red" great spot (not visible in this photo). At the cool cloud temperatures, the chemicals in the atmosphere should be colorless, so some have suggested that hydrogen compounds tint the cloud tops.  Or, maybe there's sulfur.  The clouds do indicate the altitude of the clouds--blue is the lowest, red is the highest. The colors of the clouds are ever changing! There's a cool video of the belts and zones here.

Jupiter has 67 known moons! The four largest ones (Io, Europa, Ganymede, and Callisto) were first discovered by Galileo in 1610, and they are the first objects found in the Solar System to orbit another planet. They are called the Galilean satellites. Ganymede is the largest moon in the Solar System, bigger than the planet Mercury. Europa is the smallest, slightly smaller than our own Moon. It's got a smooth bright surface covered with ice, and perhaps liquid water 100 km deep. It's a favorite of the astrobiologists in their hunt for life elsewhere in the universe.  Callisto is the second largest of the Galilean satellites and is believed to be composed of about equal amounts of rock and ices. It's a candidate for a base for a human base if we ever get that far out and explore the Jupiter system because it's the furthest from the intense radiation of Jupiter. Finally, Io, the moon that looks like a pizza, is the most active moon in the solar system, with geysers and volcanoes erupting constantly to spew sulfurous compounds into its atmosphere and across its surface.

With a reasonable telescope, you'll be able to see these moons during the opposition!

Warm Gjulf Stream may portend energetic spring-time storms in the midwest

From Washington Post Capital Weather Gang on 3/22/17.

Weather in the Midwest is a fight between the receding Arctic cold air and the encrouching warm air from the Gulf of Mexico. The battle scars of this fight are the tornadoes of the Midwest. Today the Washingto Post summarized the current situation: "freakisly warm" waters in the Gulf of Mexico. Houston to Miami have had historically warm days (while we in the Pacific Northwest have had unusually cold and rainy times). Please see source in the figure caption for details and credits.
     The average sea surface temperature in the Gulf never fell below 73 degrees for the first time ever. Galvaston Texas broke 33 temperature records since November 1, and Houston had the warmest winter on record. Gads, I go there in a couple of weeks, and afternoon temperatures in Houston are projected to be in the 80's. Overnight temperatures have also remained high, a concern for health officials. Sea surface temperature in the Gulf is loosely correlated to tornado activity.  Additional requisites are: mixing layer with hot dry air at altitude that flows into the southern and central US to interact with this warm moist Gulf air. Another favorable ingredient is that there is a warm pool off the coast of Peru, and a cold pool of of the U.S. West coast, a pattern that correlates with high tornado activity.
    This report quotes: "A vigorous jet stream disturbance, originating from the Pacific Ocean, will crash into the southwestern United States around March 28. Once it enters the Plains around March 29 and March 30, it is likely to tap into the warm Gulf water and encounter the elevated mixed layer. Then severe storms may erupt." Not a great time to plan a cross-country trip, which is exactly what I've been doing! Will bring camera.....

Origin of the Moon--redux!

Ever since Harold Urey proposed his theory for the origin of the Moon in 1952, it's origin has been the topic of debate, a debate that has not yet been settled.  One of the goals of the manned space program to the Moon was to get samples that would solve this debate but, because the Moon has undergone differentiation and a complicated geological history, we know a lot about the evolution of the Moon, but not about its origin.  In Nature Geoscience (v. 10, pp. 89-94, 2017) Rufu, Aharonson and Perets advance a theory that the Moon was formed, not by a single impact of a Mars-sized planetesimal as in the current paradigm, but by a series of smaller impacts.
     Some of the constraints that must be satisfied by a theory of origin are as follows.  The Moon is massive relative to its planet compared to Moons around other bodies in the Solar System.  The Earth-Moon system exhibits an unusually large amount of angular momentum. The Moon is depleted in volatile elements compared to carbonaceous chondrites which are taken as representative of undifferentiated planetary material.  This depletion is taken to indicate that some highly energetic process heated the moon. In contrast, rarefactory elements, such as Ca, Al, Ti, Ba, Sr,..., are enhanced. Iron is depleted relative to its abundance in the earth. The oxygen isotope compositions for the earth and Moon are similar, a fact that suggests that they were formed from the same material and their relative values compared to other bodies in the Solar System suggests that they were formed in the same vicinity.
     A major problem with single-impact scenarios is that a single impact cannot provide the observed angular momentum.  Rufu et al. argue that the largest impactor is also not necessarily the last one, and that multiple impacts are needed to provide both the observed angular momentum and observed mass. 
     Rufu et al. point out that computer simulations of impacts show that the projectile contributes more than 70% the the mass of the Earth-orbiting disk in which the ejecta land to later accrete into a single Moon. This so-called "skewed mass" contribution of the impactor is a problem because it is unlikely that the impactor and the proto-earth would have the same composition.  How can the Earth and Moon be isotopically similar in oxygen, titanium, tungsten?? In the multi-impact scenario proposed by these authors the proto-Earth experiences a number of collisions by bodies ranging in mass from 0.01 to 0.1 times the mass of the proto-Earth as shown in this figure from the paper:

Multi-impact scenario for

     Figure caption: Each impact by one of the small bodies generates a disk of material from which a small satellite forms.  These small satellites migrate outward under the influence of tidal interactions, and end up at their "Hill radii" to eventually coalesce to form the final Moon. The Hill radius for the Earth is the region in which the Earth dominates the attraction of satellites. 
    
Using computer simulations of multiple impacts in which parameters for the impactor mass ratio, speed, direction angle, and planetary rotation were varied, they examined whether or not the earth gained or lost material due to the impact. They found that lower impact angles favored planetary erosion over planetary accretion for the earth. They also found that it was difficult to make a Moon of the current mass from an impact, and that it was easier to create a number of sub-lunar mass disks sequentially, from which the Moon formed by the merger of multiple moonlets as shown in the figure.








    

Large Rogue Wave Detected by a Buoy

The Great Wave of Kanagawa by Katsushika Hokusai

One of the most popular chapters in my book "The Dynamics of Disaster" is the chapter on rogue waves. BBC.com reported that the World Meteorological Organization reported a 19-meter (62.3 ft) wave that occurred on Feb. 4, 2013. The wave was driven by 50.4 mph winds. It was, according to the WMO, higher than the previous record of 18.275 meeters (59.96 ft). Both of these waves were in the North Atlantic.
      (Contrary to popular belief, the Great Wave of Kanagawa pictured to the left is not a tsunami, but a rogue wave.)
     I don't know if it's the WMO or CNN, but the claims that these are record breaking waves recorded by buoys seems erroneous. As I discussed in my book, waves near to or greater than 100' in height were recorded from the 1990's onward as more and more instruments were deployed in the oceans.  One wave of 100.7 feet height, and the struggle of a fishing boat, the Andrea Gail, with these waves became the basis for "The Perfect Storm" by Sebastian Junger and a 2000 box hit movie by Warner Brothers.
    Although not recorded by a buoy, but by a laser on a drilling platform in the North Sea, the famous Draupner Wave reached a trough-to-crest height of 86 feet. On most days, waves around the Draupner platform on which the laser device was mounted averaged 10 feet. On that day, the so-called significant wave height was 36-40 feet. From statistics, the maximum height for these conditions would have been about 66 feet, so the 86' high wave was quite the exception.
     In 2000, the European Space Agency (ESA0 tried to quantify the frequency and size of rogue waves. Within a year of the start of the effort, two boats, the Bremen and the Caledonian Star, were hit by waves at least 100' in height, and over three weeks around this time, the satellites spoted ten waves higher than 80'. Waves up to 100 feet tall are most commonly found in the North Atlantic, North Pacific, and in the Pacific Ocean southwest of Australia and near Cape Horn. The average likelihood of encountering waves exceeding 36' in height along the main shipping routes in the North Atlantic is about 1%/day!

If you don't think that life can change in a second, dig this!

Cows stranded by earthquake/landslide New Zealand from NPR

AP wrote a story about these stranded cows and called it "Nowhere to Moove." At this time, it's not clear what the fate of these cows is/will be.
   I won't try to summarize the science of the November 14 New Zealand earthquake, but recommend Temblor by David Jacobson and Ross Stein. There were 2 deaths and a 6-8' high tsunami on the east coast of the South Island. The earthquake was about 60 miles north of Christchurch. Temblor reports that it was not one fault that ruptured, but four, including one that had not previously been recognized in Waipipi Bay. Displacement reached 33 feet. See the Temblor site for some spectacular pictures.

UPDATE on 11/15: Cows have been rescued!! 

Bubbles in Beer, Dust in Air, and Why they Matter

I'm giving a talk this weekend at a meeting of the Jefferson Land Trust in Port Townsend. One of the points of the talk is that fluids of interest in geological processes can have some very unusual and unexpected properties. One example relates to the speed of sound in a liquid or gas.  The speed of sound in liquid water is about 1400 meters per second, basically a mile per second. That's fast compared to geological processes which typically have speeds less than a few hundred meters per second. But, if the liquid has gas bubbles, for example boiling water, the sound speed is dramatically depressed. Why? Consider first a simpler fluid than boiling water: beer. The sound speed (squared) is defined as the inverse of the compressibility*density.  Compressibility is "squishiness." Water isn't very squishy (as anyone who has done a belly flop off of a diving board knows), but if you add bubbles, things change (there's a reason that Olympic high-divers plunge into an aerated part of the pool). The density isn't affect much at all by the presence of small bubbles, but the squishiness is dramatically changed--the bubbly beer has almost got the squishiness of the bubbles. So, since the squishiness is in the denominator, the sound speed dramatically decreases--down to about 10 m/s. If the bubbles are steam in water, instead of air, there are other processes (condensation and evaporation of the steam as sound waves pass) the sound speed can be even lower, as low as 1 m/s. That means that if we walk at a pace of ~20 minutes per mile, and could walk through boiling water, we would be walking at Mach 2!!

     There's another situation in which low sound speeds can occur in geologic processes: dusty gases. The sound speed of a pure gas is inversely proportional to its molecular weight. The higher the molecular weight, the lower the sound speed: Helium ~ 970 m/s; Air ~340 m/s; Freon 12 ~150 m/s. I haven't done a lot of research on particle concentrations in dust storms, but in one study in Australia, concentrations of 10 mg/m3 for just the breathable particles were reported. If anyone wants to help convert this to mass fraction (mass ratio solids:vapor), help is welcomed!
     It is very difficult to determine particle loading in volcanic eruptions. Any sensors in the path of advancing gas/particle clouds are destroyed, but remote sensing techniques are improving.  The bottom line is that particle loading in destructive emissions are high compared to even desert dust storms, thus their destructiveness. These flows can be "internally supersonic," that is, supersonic inside themselves, but subsonic compared to atmospheric sound speeds (~340 m/s). Thus, they don't generate shock waves. The lateral blast at Mount St. Helens did not generate atmospheric shock waves. It did generate compression waves as the blast pushed on the atmosphere, and due to the complex structure of the atmosphere, these waves steepened into audible acoustic waves to the north, e.g., hear in Vancouver B.C.
     Bottom line: there are shocks and there are shocks. Some are inside these wierd geological flows, and others are in the domain of atmospheric sciences.

Anatomy of a hurricane

Added October 6: Here's a nice site to track the projected path of the hurricane.

Here's a nice graphic from AccuWeather on the anatomy of a hurricane showing conditions likely to occur in the four quadrants. There is speculation that this may be one of the rare hurricanes that loops around back on its earlier track, but the models are changing very rapidly.
     As Hurricane Matthew bears down on Haiti, it is worth reflecting on why Haiti seems to suffer so badly from hurricanes and floods. It may or may not see a disproportionately large number of hurricanes. Prior to 2008, only six major Category 3 or stronger hurricanes had struck Haiti since 1851. Cleo in 1964 killed 192 people; Flora in 1963 killed 8000. But in 2008, four storms (Fay, Gustav, Hanna and Ike) struck.
     However, given these storms, Haiti suffers a disproportionate amount of flooding (see Jeff Masters article here).  Charcoal from burnt trees had provided more than 85% of the energy in Haiti for decades and at present it's something like 60%.  This has resulted in denuded mountain slopes that cannot absorb and hold back the deluges of rainwater. For an interesting take (and references) on whether or not Haiti is as heavily deforested as popularly believed, or less so, see the interesting post in Envirosociety.org here.

Massive sinkhole in Florida

Just a short post to call attention to this spectacular and potentially dangerous sinkhole in Florida that is putting toxic water into an aquifer.

Louisana floods of August, 2016

Photo from KOMONEWS.COM, Scott Sistek blog

Residing in Seattle, I know how much rain we get in the winter--southeastern Seattle got all of that rain in 48 hours from a stalled area of low pressure that tapped into tropical moisture. This post is largely a summary of Scott Sistek's blog post here.  Several thousand people have been rescued from flooded areas and the governor (who had to evacuate the Governor's Mansion in Baton Rouge) said that they "haven't been rescuing people. We've been rescuing subdivisions."

     The town of Lafayette in the wettest part of the storm reported 10.39" of rain on Friday, a record that toppled in one day when they reported 10.40" on Saturday. This combined total of 20.79" for two days is about what we get in Seattle in an average november+December+January+February (20.99"). The record had been 10.38" and it went from first place to third place in just two days! Baton Rouge had 16.71" in the same 48 hours. 

Radar showing estimated 20"+ in purple. From same source as above.

     The moisture was dragged moisture from the Gulf over the region as it drifted very slowly to the west. While these regions typically experience heavy rains, it is unusual for a storm to stall like this. When I looked at weather.com weather forecast, there is another week of rain and thunderstorms (though the rainfall amounts should be less) and 85-87 degree temperatures. 

     According to weather.com, the storm is heading north and will bring heavy rain into the midwest--St. Louis (5-8" there and in central-eastern Illinois), Indianapolis, Cincinnati, Columbus, Cleveland and northwestern Pennsylvania (1"). A number of weather systems are colliding--the stalled low pressure region, moisture heading north out of the Gulf of Mexico, and cool, dry air from Canada heading south.The same pattern is staying in place for a few days. Hot, humid, rainy conditions are also predicted for my University of Illinois friends in Champaign, IL, with a flash flood watch in place as I write this (Sunday afternoon). 

     I hope that all of those affected by this storm take care of themselves and others, and wish you a speedy recovery.

The Environmental Fall of the Roman Empire: Review of an article

The Roman Empire at its height, 117 A.D. From Huffington Post Oct. 12, 2015

In Daedalus, the Journal of the American Academy of Arts and Sciences, v. 145(2), pp. 101-112, Spring, 2016, I found an interesting article by Kyle Harper, a Historian and Professor of Classics and Letters at Univ. of Oklahoma, also Senior Vice President and Provost. The article is titled "The Environmental Fall of the Roman Empire." Since this publication isn't easily available, and I wanted to review the article, I'll summarize it here.

ALERT: I find this article very interesting, but also have some question about the facts, e.g., on p. 108 he refers to a "massive volcanic eruption in AD 169" for which I cannot find any documentation in the volcanology literature. In a reference (Sigl et al., Nature 523, p. 543-549, 2015, there is an "unattributed event" in AD 169.

The article begins with a description of festivites in 248 AD, the thousandth anniversary of Rome. The emperor at the time was Marcus Julius Philippus, "Philip the Arab," who hailed from the southern reaches of Syria. Harper's thesis is that these festivities hid the fact that Rome was already in decline and that, within the space of the next generation when Aurelius would be emperor, the decline was set in. Harper then comments that Gibbon's famous "Decline and Fall of the Roman Empire" of the late 18th century was written from the perspective of its time, when the role of environmental change was not thorougly explored. Data provided from ice cores, tree rings, marine deposits and cave minerals allow historians to reconstruct climate history on "civilizational time-scales with razor precision."
     Accumulated evidence suggests that Romans were short in stature, the average man standing 5'5" tall. Harper takes this as a measure that the resources that contribute to human health were already stressed. Human health is a function of both genes and the environment, the environment being critical to providing nutrition. The short stature, he hypothesizes, was due to a heavy burden of infectious disease that "drained their bodies' metabolic resources and stunted their growth." The environment, in this view, contributed to ill health (he discusses, but discards, Gibbon's thesis that the problems were either endogenous or exogenous but due to the "inevitable effect of immoderate greatness," i.e., overexpansion.
     Rome grew from a collection of small huts along the Tiber River rather slowly and fairly locally through many centuries until roughly the second century BC, e.g., as possibly defined by the Battle of Carthage in 149 BC. After the Romans razed Carthage, they controlled the Mediterranean, referring to it as mare nostrum, "our sea." The built an agrarian tributary empire that extended north to the 56th parallel down to the 24th parallel, from mid-latitudes to the edges of the tropics. This environment, particularly close to the Mediterranean, is a delicate and complex ecosystem, consisting of a patchwork of microclimates. The western territories are under the influence of Atlantic Ocean patterns, whereas the Eastern Mediterranean is influenced by this but also by other systems that influenced winter precipitation. Egypt, "the breadbasket of the Empire" was yet another climate regime. Movement of food over this huge area was expedited by the huge road system and control of shipping lanes in the Mediterranean. Malthus's "gigantic inevitable famine" hit the Romans only through times of relatively high prices. (Malthus, BTW, published just a decade after Gibbons.) Just as innovations in agricultural fertilization in the 20th century avoided the Malthusian consequences of soaring planetary population, trade and technological improvements forestalled limits on the productivity of land controlled by the Romans. And, just as we have been in a period of climate hospitality at present, there was a period called the "Roman climate optimum" in the late Holocene for the Mediterranean climate. Climate, commerce and technical progress allowed enormous population growth. Though, signs of stress were present in the short stature and low life expectancy (even by ancient standards). Summers were characterized by gastroenteric illnesses, autumns by malaria. "The Romans were rich, but sick."
     In the 160's A.D., smallpox struck, probably brought in along the trade routes from the Red Sea.It was the so-called Antonine Plague, perhaps the world's first pandemic.The benign climate that had blessed the Empire for a long time came to an end, perhaps with the mysterious AD 169 eruption that I mentioned above, but whatever the cause, for the next few centuries the climate began a descent into the "late antique little ice age." In AD 244 and 246, the Nile waters failed to rise. The price of wheat rose, and the food crisis in Egypt was felt throughout the Empire. One purpose of the millenium AD 248 games was to "ward off the evils of pestilence." The Plague of Cyprian (a bishop of Carthage who described the disease) ravaged the empire from AD249 for about 20 years. Alexandria, where it started, lost 62% of its urban population, 5000 corpses per day were wheeled out of Rome. Barbarians, who had previously been repelled rampaged, and the Empire started dissolving.The fabled Roman coinage collapsed and inflation ran rampant until gold was brought back as coinage. Later in the late third century, a very different empire arose.
     Harper concludes by pointing out that historians have mountains of new knowledge about ancient environments due to scientific advances. Earlier historians tried to explain the events of the first centuries AD without knowing the evidence about climate change and disease. "The proud urban people who cheered in the circus, or sang in the processions of the ludi saeculares in AD 248, could little have imagined that dynamic cycles in our proximate star, or the chance mutation of a virus in a far-off forest, would rattle the foundations of the familiar world they inhabited."...."an occasional and wary glimpse to the present?????

P.S. Note that there is also a literature on the role of lead poisoning, but it has become increasingly controversial, e.g., this article.

Deadly Mount Sinabung eruption, May 21, 2016

Sinabung as viewed from the east.
Photo by Tom Casadevall, U.S.G.S., 1987

Mount Sinabung in the North Sumatra province of Indonesia, erupted on Saturday killing seven people in a village.  The village, Gembar, is one of four villages inside a 2.5 mile danger zone from which 5,000 residents were evacuated at the time. Villagers still enter the zone intermittently to tend to property. A video showing parts of the eruption and its ashy aftermath is available from The Guardian here.
     Sinabung is a highly active stratovolcano that rises to an elevation of 2460 meters. It is part of a subduction zone setting where the continental crust is >25 kilometers thick. The major products are andesite, basaltic andesite and dacite. There are four active craters at the summit. All four craters discharge sulfurous gases and form sulfur deposits which are mined by the local people.
    There are unconfirmed reports of an eruption in 1881, and solfataric activity was noted high on the volcano in 1912. It appeared to be dormant from this date until an explosive eruptions (VEI 2) in the summer of 2010. The eruption of August 27th was phreatic, with the initial emission of a grayish white plume followed by black plumes that reached 2000 m above the crater. The rocks and ash erupted came from altered rock in the crater and its deeper hydrothermal system.
    The events of 2010 were followed by a lava dome-forming eruption accompanied by explosive eruptions in September, 2013. Lava extrusion continued through 2014 at a rate of about 3.5 cubic meters per second, reaching about 0.1 cubic kilometer in volume. Sixteen people were killed in February 2014, and 30,000 local residents had to be evacuated. Magma mixing before the eruption is indicated by the presence of magic blobs and "plagioclase microlites more calcic than the phenocryst rims," and absence of a reaction rim on hornblende phenocrysts (Nakada et al., AGU abstract, 2014).
     As of the date of this post, the area remains under high alert and efforts are being made to evacuate any people in the danger zone.

A call for upgrading America's infrastructure and, in particular, aging dams

Hoover Dam, photo by Mike Blake, Reuters
Image from the article cited in text

I'm not going to summarize the article linked here, but having worked around dams, I truly believe the conclusions of this writer: major investment required to date infrastructure that dates back to the end of WWII, or even before.

Lightning strikes kill 65 people in four days

Rickshaw drivers in rain in Dhaka. Image from CNN article referenced.

 

 

CNN reports that the number of people being killed by lightning strikes in Bangladesh has increased dramatically: last Thursday 34 died, 21 on Friday, 7 on Saturday and 3 on Sunday. Officials say that deforestation has "exacerbated the problem" with farmers working in open fields now where they are targets for lightning strikes. For comparison, five people have been killed so far this year in the U.S. despite our population being double that of Bangladesh.
     According to UCAR, there are more than 3 million lightning flashes worldwide per day. That equates to >30 flashes per second. The majority of lightning flashes are within clouds or between clouds. These outnumber cloud-to-ground strikes by about a factor of six in tropical storms, by a factor of two in midlatitudes. (I strongly recommend this UCAR link for well-explained snippets of interesting information about lightning!)
     What purpose does lightning serve on the earth? The earth's crust is negatively charged but the ionosphere (a layer in the atmosphere above 50 kilometers) is positively charged. The atmosphere between these two regions is slightly conductive which allows current to flow between these two regions. The earth-atmosphere potential "would disappear in a mere five minutes" were it not for lightning which, on a global scale, acts to separate charges on atoms.

NOAA image

     This mechanism overrides the fact that on the scale of a single thunderstorm, lightning releases electrical energy built up by the storm. Thunderstorms contain a lot of ice crystals and hailstones. Meteorologists believe, though the reasons are not well understood, that millions of collisions among these small solid particles cause the storms to evolve with a positive charge near their tops and a negative charge lower down. In a typical cloud-to-ground lightning strike, negative charge descends to the ground and the objects struck release a positive charge upward. The net effect keeps the charge of the earths crust negative.
    One of the more fascinating explanations on this page tells how a cloud-to-ground flash evolves. A series of "stepped leaders" move a bundle of charge a distance of only about one city block. Each step takes about a microsecond, followed by a pause of about 50 microseconds, and then another step.  At each step, the evolving bolt may change direction toward a stronger electric field area, resulting in a final flash that is full of zigs and zags. On the ground, there may be several regions of opposite charge, causing the bolt to split into several branches as it nears the ground. Just before reaching the ground, the leading step induces an electric potential of some 10 million volts. This is sufficient to bring up surges of positive charge from sharp objects or irregularities near the ground. Once the negative tip of the bolt and the rising surge of positive charges meet, typically a few tens of meters above the ground, the connection between the cloud and ground is established. The return stroke "zips upward at a rate much faster than the stepped leaders descent." It is this return stroke that produces the visible flash.  Air surrounding the bolt is heated to about 30,000 C (54,000 F), creating the shock wave that we register as thunder.
     Finally, I can't do better than to print the whole UCAR instruction on how to avoid being struck by lightning:

"How can I avoid being struck by lightning?

Going indoors during a thunderstorm is by far the best way to avoid lightning. New guidelines recommend taking shelter as soon as you notice thunder arriving less than 30 seconds after a lightning flash. Since it takes five seconds for thunder to travel one mile, the 30-second interval means a flash is less than six miles away. This, in turn, means that the next flash might strike your area soon. Outdoor activities such as baseball or football games should be interrupted for shelter as soon as the 30-second rule is met. (An entire football team of 11 players was killed by a lightning strike in Africa in the fall of 1998.)
Shelter is not failsafe. Lightning can strike though telephones, except for the cellular variety. You should avoid taking showers or standing by windows, screen doors, or patios. To protect household appliances, unplug them before (but not during!) electrical storms.
Outdoors, the idea is to avoid being near--or being--the highest object around. Get away from isolated trees, metal fences, wire clotheslines, and the like, and avoid standing in an exposed area or near water. If you are the tallest thing around, or in a boat on open water, crouch down to reduce your height (but don't lie flat). Lay down metal sports equipment and dismount bicycles. Take especially swift action if your hair stands on end, as that means charged particles are starting to use your body as a pathway. The safest form of vehicle is one with a fully enclosed, all-metal body, which helps to channel electricity around the interior. Make sure the car's windows and doors are completely closed.
Finally, remember that lightning can, and often does, strike the same spot more than once--even the same person. U.S. park ranger Roy Sullivan reportedly was struck seven times between 1942 and 1977."

New model for the Ries impact crater, Germany

I haven't worked much on meteorite impact craters for about 20 years, and have been delighted to find how much the concepts have changed since Chuck Simonds and I published our ideas about the role of volatiles and lithology in impacts back in 1980. The dramatic increase in our understanding results from two factors: over a half century of detailed work by (mostly) German geologists documenting the Ries in detail at all scales, and the dramatic increase in computational capacity since the 1980's. I reproduce here a figure from Stoffler et al. (2013) and a brief description of the five phases of an impact that they discuss. Strongly recommend the original papers. The impact scenario is for formation of the 24-kilometer Ries Crater in Germany, about 14.5 million years ago.  It's a favorite spot for meteorite enthusiasts, not the least because in the village of Nordlingen, a church is constructed from one of the impact products, suevite!

·      Phase 1, panel a: Impact phase, about 2 milliseconds after impact;

·      Phase 2, panel b: Primary ejecta plume and final shape of the transient cavity; ejecta curtain and clast-laden impact melt layer, about 10 seconds after impact;

·      Phase 3, panel c: fully developed primary ejecta plume, crater shape after collapse of transient cavity; formation of central uplift, and innermost ejecta blanket, the Bunte Breccia from deposition by the ejecta curtaint; about 40 seconds after impact, and
     Phase 3, panel d: buoyant primary ejecta plume begins collapsing,  deposition of Bunte     Breccia; slumping of volatile-containing sediments into the hot melt pool begins; about 2 minutes after impact

·      Phase 4, panel e: Secondary plume(s) formed by reaction of the hot melt pool with water for a fuel-coolant-interaction (FCI) process is fully developed, time = days to months;

·      Phase 4, panel f: Collapse of the FCI-induced secondary plume(s) and early phase deposition of outer suevite and part of crater suevite. Time = minutes to tens of minutes after start of FCI

·      Phase 4, panel g: late phase of secondary plume(s) and deposition of the main mass of crater suevite-time scale of months to years

·      Phase 5, panel h: final crater with all units in place, before formation of a crater lake if that happens. Time – months to years after impact.

References:

    Kieffer,  S. and Simonds, C., The role of volatiles and lithology in the impact cratering process, Reviews of Geophysics and Space Physics, 18(1), 143-181, 1980.

    Stoffler, D., et al., Ries crater and suevite revisited--Observations and modeling Part I: Observations, Meteoritics and Planetary Science 48 (4), 515-589, 2013.

    Artemieva, N.A., Ries crater and suevite revisited--Observations and modeling Part II: Modeling, Meteoritics and Planetary Science 48(4), 590-627, 2013.