Welcome!

This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com


Tuesday, September 24, 2019

Artist's documentation of human effects on the planet

A photographer/artist Edward Burtynsky has produced a beautiful documentation of the impact of the human species on the planet: 

https://www.bbc.com/reel/video/p07nxv77/artist-captures-how-humans-are-reshaping-the-planet

Friday, August 9, 2019

Glacial outburst from Mount Rainier Monday night!

From The New Tribune
A small glacial outburst from the South Tahoma Glacier on Mount Rainier occurred on Monday night, closing a road and trail in the national park. The glacier is on the southwest side of the mountain. Park staff noticed that Tahoma Creek had turned muddy grey with sediment. At least 32 such floods have occurred in the last 52 years. Geologists anticipate that more outbursts could occur in the next weeks to months. A video is available in the article by Craig Sailor at The News Tribune.

Friday, July 12, 2019

Earthquake!

Arrow points approximately to our location!
In the early hours of this morning (2:51 a.m.), a M4.6 earthquake struck under the town of Monroe, east of Everett (red star).  We and many friends (black arrow), were awakened by shaking and rattling! I haven't been woken up by an earthquake in more than 50 years! We reported it to the USGS site where they gather data on how far the earthquake was felt; the map to the left compiled from such reports shows that the shaking intensity was V or less around Puget Sound.
    This was a deep earthquake--24.3 km.  A M3.5 aftershock occurred less than 2 minutes later at a depth of 30.1 km, within the crust of the North American plate. There have been no reports of injuries, and a few reports of cracks in foundations near the epicenter. The quake was not on the Cascadia subduction zone. The Nisqually earthquake of 2001 with M6.8 near Olympia was in the subduction zone and was within the Juan de Fuca plate.
     There is an excellent summary of the types of earthquakes that occur in the Pacific Northwest here. As of 10:30 PDT this morning, there have been a number of small aftershocks.
      The nearest big fault is the South Whidbey Fault, which runs southeast from the Strait of Juan de Fuca toward Monroe (to the south of Monroe). The motion along this fault is strike-slip/reverse thrusting.  According to UW seismologist Bill Steele, it looks like the quake originated "from a cluster of faults running north-south from Duvall", that is, it was not along the South Whidbey Fault.  In 1996 a M5.4 earthquake near Duvall caused millions in damage, but that quake was shallower as well as stronger than this one. In a video on this King5 site, he explains that the motion was tensile, that is, the ground pulled apart. The Early Warning System gave 3-4 seconds warning in Seattle.
    Here is a short article on the South Whidbey Island fault zone from the Department of Natural Resources, WA. And, below is a reproduction from the University of Washington website on the South Whidbey Fault:
    
"Much of the Southern Whidbey Island fault zone (SWIF), which runs in a north-westward direction from Woodinville to near Port Townsend, Washington, remains mostly hidden. Geologists conclude that the SWIF is capable of producing a M6.5 to M7.4 earthquake (Kelsey et al., 2004).  The ground shaking expected for a M7.4 earthquake is shown in the ShakeMap below. As with other crustal faults, any moderate or large earthquake on the SWIF will likely be followed by numerous felt aftershocks, some that could be damaging, and hundreds to thousands of smaller ones detectable only by sensitive instruments.
Southern Whidbey Island ShakeMap
‘ShakeMap’ showing the intensity of ground shaking (colors) expected for a M7.4 earthquake on a segment of the South Whidbey Island fault (white line indicates intersection of the causative fault with the surface), overlain on topography.
     "The SWIF was first discovered because movements along it juxtaposed older crystalline bedrock next to younger volcanic basalts (Johnson et al., 1996). These rocks have contrasting densities and magnetic properties that were measured and mapped by Gower et al. (1985), and attributed to motions along a single fault. Subsequent studies showed that numerous fault strands comprise the SWIF, located within a 6-11 km (3.7-6.8 mile) wide band.
      "These faults dip steeply to the northeast and have had north-side-up and lateral displacements, and are visible at the Earth’s surface only about every 35 km (22 miles).These studies used seismic reflection data, sea cliff exposures, and sparse borehole data to map the SWIF to the eastern Strait of Juan de Fuca (Johnson et al., 1996), while others used seismic imaging methods to steer the fault along the northwestern margin of the Port Townsend basin, where it may merge with the Darrington-Devils Mountain fault zone near Victoria, British Columbia (Broker at Al, 2005; Ramachandran et al., 2005). If these interpretations are correct, the SWIF extends a minimum of 150 km (92 miles) from Victoria, British Colombia, to near Woodinville, Washington.
     "Evidence that the SWIF has been recently active comes from high-resolution seismic images and measurements documenting uplift of the shorelines that straddle the faults, along two coastal marshes on Whidbey Island, at Hancock Lake on the south side of the SWIF and Crockett Lake on the north side (Kelsey et al., 2004). If no movement on the fault strand occurred in the latter part of the last 10,000 years (Holocene epoch) both sites should have comparable sea-level histories. However, stratigraphic observations and radiocarbon dates used to construct relative sea level curves for each site diverge between 2800 and 3200 years ago, suggesting uplift of about 1 to 2 m (3.3 to 6.6 feet) along the north side of the fault strand. This amount of uplift was likely generated by a M6.5 to M7.0 earthquake, according to empirical relationships between vertical displacement versus magnitude for historical earthquakes (Kelsey et al., 2004).
"Earthquakes on the SWIF probably caused at least three episodes of strong ground shaking and one tsunami in the last 1200 years. Geologists studied the stratigraphy of channel bank exposures along the Snohomish River near Everett, Washington reveal and infer that a widespread pairing of sand overlain by clay that correlates over 20 km2 was left behind by a tsunami surge across the delta between 1200 - 1020 years ago (Bourgeois and Johnson, 2001). Multiple episodes of strong ground shaking also have been inferred from liquefaction features, sand dikes and sand-filled cracks up to 1 m (3.3 feet) wide, some of which terminate below and others that cut across the tsunami deposit and thus, pre- and post-date it (Bourgeois and Johnson, 2001).
     "More recently studies extend the record farther back in time and southward.  These suggest that the SWIF produced at least four earthquakes since deglaciation about 16,000 years ago, the most recent being less than 2700 years ago. High-resolution topography (LiDAR) and measurements of the magnetic properties of the rocks reveal lineaments indicative of fault movements.  These show that the SWIF forms a 20 km (12 miles) wide swath of parallel fault strands, that project onto the mainland near Everett and continues to the southeast towards Woodinville (Blakely et al., 2004; Sherrod et al. 2008).  The most prominent feature, the Cottage Lake lineament, extends at least 18 km (11 miles) and lies on strike with the SWIF on Whidbey Island. Excavations across visible scarps that exhibit north-side-up vertical relief of 1-5 m (3.3 to 16.4 feet) show these were created in multiple earthquakes that post-date deglaciation. 
     "Although highly speculative, geologists have suggested that the SWIF is part of a larger system of faults that extends from Victoria, reddish Columbia to Hanford, Washington a distance of about 385 km (236 miles). However, while such a system may reflect very large-scale geologic processes, no evidence exists indicating multiple zones have failed together in a single earthquake. A series of faults and folds in the Snoqualmie area of the Cascades likely correlate with the SWIF (Dragovich et al., 2007, 2008), merge with mapped faults on Rattlesnake Mountain (mapped by Tabor et al., 2000) near North Bend and continue southeast into the Cascade Mountains. Others suggest that faults in the Yakima fold and thrust belt correlate with faults west of the Cascades, based on lineaments in magnetic measurements and other observations (Blakely et al., 2009).
     "The HAZUS program provides quantitative estimates of some of the impacts of a M7.4 earthquake on the SWIF.  Examples include ~97800 buildings (~5% of the inventory) at least moderately damaged, with 6% of these damaged beyond repair.  A handful of bridges will be destroyed completely, significant fractions of the utility system will be only partially functional in the first day after the earthquake but mostly fixed within a week.  However, in excess of 100,000 households will be without potable water or power in the first day and tens of thousands still without both after a week.  Almost 14,000 households will be displaced and 58% of these will require public sheltering.  Fatality estimate range from 90 to 432 depending on the time of day the earthquake strikes.  Economic losses will be in the range of many billions of dollars."

Tuesday, July 9, 2019

JAWS=(July Abnormally Wet System) approaches!

Satellite image of JAWS on Tuesday, July 9 from Cliff Mass blot
JAWS=July Abnormally Wet System

We have a wonderful atmospheric scientist at U. Washington, Prof. Cliff Mass. He has written a blog about the Northwest weather since 2008, two years longer than my blog and has had a total of nearly 46 million page views! The material below is taken from his post today, July 9.
     Usually we get hot and dry after the July 4th holiday, but not this year! Some people are even commenting that they are still using their furnaces...  JAWS is approaching the northwest coast, and Cliff says "The view from space is scary and unusual for this time of year. It looks like a November satellite image."
     Rain approaches overnight and tomorrow will be cool (almost cold for this time of year) and wet--not just a typical Seattle drizzle, but real rain, the heaviest being overnight Tuesday-Wednesday a.m..
    Cliff likes the JAWS movie analogy--there were sequels to the original JAWS film, and there are going to be sequels to the weather system here.  JAWS2 will move in on Sunday, when another upper level trough comes through our region.  And JAWS3 will probably strike between July 19-22, possibly even producing   wetter conditions than JAWS2. 
     We have been in an interesting summer weather pattern in June and early July: unlike normal summer weather in which eastern Washington is hotter than western Washington, we have had more severe drought conditions in the west. The Puget Sound region where Seattle is located is in the lighter orange color on the Drought Monitor map, classified as D1=moderate drought.  Much of the Olympic Peninsula is the dark orange, D2=severe drought. 
     Because of these conditions, JAWS and its sequels will be welcome for lowering the fire and smoke prospects at least through July.  However, this will encourage growth of flora and if we have a hot, dry August, the forest fire and smoke conditions may return. 

Monday, July 1, 2019

Checkerboard Mesa, Utah: An example of ??

Checkerboard Mesa, Utah and companion mesa showing fracture pattern. Photo by SWK
One of the most distinctive and popular geologic features in Zion National Park, Utah, is Checkerboard Mesa near the east entrance of the Park. [Often overlooked is that it has a companion feature (at the right in the photo) showing similar features.] The distinctive features of these mesas are the sub-vertical and sub-horizontal cracks. The features, most prominent here, are actually found in a few places in the park and always on the North facing sides of slopes.

Detail of fractures. Photo by G. Lopez
 The cracks are in the Navajo Sandstone, a formation prominent in the spectacular cliffs of Zion. The Sandstone is over 2000 feet thick in the Park and is comprised of ancient desert sand dunes. The sub-horizontal lines are layers, called cross-bedding, within individual dunes. The dunes were compressed as material, now eroded, was deposited on top of them. Individual grains of sand were glued together by calcite (CaCO3) and iron oxides (which gives them the red color) to form the sandstone.
      Some details of these features are shown in the second figure. The pattern of horizontal and vertical cracks have been called a subset of  "polygonal cracks" in bedrock due to weathering (Chan et al., https://doi.org/10.1016/j.icarus.2007.09.026). As pointed out by Chan et al. , the sub-vertical cracks are, in detail, perpendicular to the layers in the wind-blown dune deposits of the Navajo Sandstone. They  change orientation when they encounter the bounding surfaces of the aeolian layers of the dunes, as shown in the detail of fractures in the second photo here. At the high elevations of these features in the Park, summers are hot and winters are cold. The north-facing orientation suggests a relation to freeze-thaw cycles that cause expansion and contraction of the rocks and cracks, a process referred to as freeze-thaw cycles.  Erosion is also enhanced by runoff from rain and water from melting snow. The Chan et al. interpretation is that the patterns are the products of tensile weathering stresses caused by temperature and moisture fluctuations (see also Loope and Burberry summary in Geosphere [14(4), 1818-1836, 2018]. These fluctuations cause expansion and contraction of the rocks, leading to the formation of the fractures through tensile stress development. Erosion is also enhanced by runoff from rain and water from melting snow.
Rectangular cracks perpendicular and parallel to bedding on Mars
     The pattern is particularly common is particularly common in porous massive sandstones found in semi-arid climates characterized by large temperature and moisture fluctuations, and has been observed in outcrops on Mars (see third figure, which is Figure 1F from Chan et al.) Cracks form perpendicular to outcrop surfaces and are thin and limited in their penetration into the host rock. Rectangular cracks form perpendicular and parallel to cross beds where the host rock is anisotropic, but where the sandstone is massive (i.e., isotropic), 5- and 6-sided polygonal forms develop. Differential erosion along the cracks compared to the polygon surfaces gives the pattern a domal relief on a microscale.

     






Friday, June 7, 2019

Bolshaya Udina Volcano on Kamchatka is awakening

Bolshaya Udina from this reference.
Until 2017, Bolshaya Udina in the Klyuchevskaya volcano group in Kamchatka was considered extinct as there is no record of past eruptions. However, in 2017 seismic activity prompted researchers to investigate the volcano, a difficult task because of its remoteness. They installed four seismic stations and monitored activity in May-June 2018. The seismic events were located at ~5 km depth. The news media (and Russian scientists) are likening the possibilties to Vesuvius in 79 A.D. or Bezymianny in 1956. Bezymianny, in turn, was a near duplicate of Mount St. Helens May 18 eruption in 1980. All are in the dangerous class of "andesitic volcanoes" which tend to have very explosive eruptions. As far as I can tell, there are no publications on the volcano other than the mention that it's a volcanic "massif" consisting of two stratovolcanoes SE of Tolbachik volcano.  It is 2923 m high (~9650 feet) and has a lava dome on its SW flank. The cluster of seismic events connects Bolshaya Udina with the Tolud zone to the southwest--a zone where seismicity in the middle and lower crust that is believed to have fed the Tolbachik fissure eruptions.  The magma has migrated from this zone toward Udina.  The low shear velocities measured suggest that the zone is rich in melt and volatiles. For more information on Udina, see Koulakov et al., JVGR 379, 45-59, 2019.
        There was an interesting paper** published in 2017 about three close neighbor volcanoes: Klyuchevskoy, Bezymianny, and Tolbachik (see map). They are among the most active volcanoes in the world and yet have very different eruption styles.  Klyuchevskoy has basaltic lavas supplied from a reservoir at about 25-30 km depth through a vertical conduit. Bezymianny's magma comes through a dispersed system of reservoirs in the crust. In these reservoirs, the andesitic component separates from the more mafic component and rises into the upper crust where it can erupt explosively.  Tolbachik has low-viscosity basalts that ascend through fractures associated with intersections of regional faults.

**Koulakov, I., et al., JGR-Solid Earth, 122(5), pp. 3852-3874, 2017.

Wednesday, February 20, 2019


Wave Rock, southwestern Australia: 14-15 meters high, 110 meters long. This feature is on the north side of "Hyden Rock", a hill made of granite.  The hill is an "inselberg" (also called a monadnock), an isolated small mountain rising from a virtually level plain. The word "inselberg" comes from German and means "island mountain." They are common in Africa.
     The indigenous people of south western Australia are the Ballardong people. In their Dreamtime, the rock was created by the Rainbow Serpent after she drank all of the water in the land. She became bloated and dragged her swollen body over the land, leaving Wave Rock in her wake. The dreaming trail of this story extends from the south coast near Augusta to the northeast to the Great Victoria Desert.
     Wave Rock is part of Hyden Rock, a 2.63 billion year-old monzogranite (reference from Wiki). The inselberg consists of three domes, two of which are separated by a valley now filled with a reservoir. Between 100-130 million years ago, granite bedrock was fractured and altered by weathering to varying depths by a process known as lateritisation (a process that occurs in hot wet climates and produces a weathered product rich in iron and aluminum). This process formed
underground pods or domes of solid unweathered granite separated by deeply weathered fragments of granite. Erosion then exposed these domes to become what is now Hayden Rock. Geomorphologists call features like Wave Rock a "flared slope,"a bedrock surface that is concave-upward. Chemical weathering around the base of an inselberg preferentially develops at the base, producing a weathered and disaggregated zone.  When the land surface around the buried inselberg is then exposed as the land surface is lowered, this disaggregated zone is easily eroded, leaving the flared slope of Wave Rock.
     A wall on top was built in the 1920's to guide rainwater (in this very arid area) toward the Hyden Humps Dam.

Monday, February 4, 2019

Great shock wave sequence in Space X Raptor Enginer Test Fire

In the first few seconds of this Space X engine test fire, there is a brief, but great, sequence of shock waves in the exhaust plume. https://www.cnn.com/videos/business/2019/02/04/spacex-raptor-engine-test-fire.cnn-business/video/playlists/business-news/. The sequence repeats about 2/3 of the way through. This is a well known phenomenon with structures as explained in the graphic.

Tuesday, January 29, 2019

Polar Vortex Explained

Much is being written about the outbreak of cold air today and tomorrow in the U.S. Midwest.  I'm not going to contribute to this other than to post a link here to the best article that I've seen explaining the dynamics (and why the cold blast does not mean that global warming is a hoax...) The author, Jennifer Francis, is a Senior Scientist at Woods Hole Research Center and a Visiting Professor at Rutgers University.

Wednesday, December 19, 2018

An unusual tornado in the state of Washington!!

From baynews9.com, no copyright information given on site
About 25 miles as the crows fly, clouds were so dark and ominous yesterday afternoon that I was having flashbacks to the low dark clouds of the midwest during tornado season--April, May.... But no! It was the setting for an unusual and rare hurricane in the state of Washington (we typically have 2.5 tornados/year and they tend to be out in the plains of eastern Washington). The tornado touched down in Port Orchard on the Kitsap peninsula.
       As of today, they've estimated it was an EF-2, with winds possibly up to 130 mph. It traveled 1.4 miles. One radio broadcast today said that they have over 400 structures to evaluate for damage, and they have to do it in a rush because another wind storn us expected tomorrow night (the last one left 100,000-200,000 people without power for hours). Note in the photo how shallow the root system is on our big evergreen trees.
     As usual, Cliff Mass, atmospheric sciences professor at the University of Washington, has posted a detailed analysis of this event and I recommend it for details.  The interesting dynamics that he emphasizes are that none of the settings that meteorologists look for were flashing alarm bells: (1) there was an area of high reflectivity (=heavy precipitation) over Port Orchard, but nothing particularly distinguishing it from other convective cells. (2) The strength of the convective cell, as measured by its height, was "pretty wimpy"--15,000-20,000 feet. (3) Doppler radar imagery showed only a weak hint at rotation, an essential component for spinning up a tornado. (4) The CAPE values indicating available potential energy were modest; (5) There was no sign of the "hooked echo" in the reflectivity.  (6) Wind shear did exist, but was modest. This was not a super-cell thunderstorm.
    The wind shear existed in the lee of the Olympic Mountains. Weak winds existed east of the Olympics (in the lee side of the Cascades) and stronger south-westerly winds came around the southern flanks. As one of the convective cells moved into the lee of the Olympics, it ingested the air containing the shear and spun up into the tornado.
     The National Weather Service did not issue a tornado alert but, interestingly, a group "Washington Weather Chasers" sent out an alert to their subscribers at 1:37 p.m. warning of a "strong rotating thunderstorm moving into the ares. Will be south of Port Orchard around 1:50 p.m...." About 10 minutes later, the tornado touched down. Good work WWC!

Tuesday, June 26, 2018

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.

Tuesday, June 19, 2018

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!


Wednesday, May 9, 2018

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!
 

Friday, May 4, 2018

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).
     




Saturday, April 14, 2018

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.   

Tuesday, September 19, 2017

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.

Monday, September 11, 2017

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.

Wednesday, September 6, 2017

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.

Wednesday, August 9, 2017

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.)

Friday, July 14, 2017

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!

Wednesday, June 14, 2017

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.

Friday, April 21, 2017

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!

Thursday, April 6, 2017

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!


Wednesday, March 22, 2017

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.....

Thursday, March 2, 2017

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.








    

Wednesday, December 14, 2016

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!