Fight for Cairo on Bridge: A dangerous place--from a fluid mechanics view

The crowds on the Kasr al-Nil Bridge in Cairo on Jan. 28, 2011
Photo by Peter Macdiamid/Getty Images
Published in the New York Times on-line on the date above

A crucial moment in the unfolding events in Egypt occurred when the crowds of protestors tried to cross the Kasr al-Nil Bridge in Cairo tried to reach Liberation Square by crossing this bridge.  Riot police kept them at bay by using gas, water canons, and truncheons. The situation is described in this NYTimes article. The battle between the protesters and the police ebbed and flowed for more than 6 hours.

What does this have to do with fluid mechanics? A lot--as you can see in the picture, a large number of people are trying to squeeze from the streets into the confined space on the bridge.  There is a law in fluid mechanics called "conservation of mass."  In the broad street or park approaching the bridge, the number of people moving toward the bridge is given by their density times their forward velocity. You can think of it as the number of "lanes" of people moving forward times the velocity that they are moving in the lanes. On the bridge, the same law applies, but the number of lanes is greatly reduced.  For a steady state, the flux of people has to be the same, which means that the people on the bridge should be moving much faster than the ones approaching the bridge.

Of course, this can't happen in a crowd, and so the bridge gets jammed--even without riot police at the far end.  This situation occurs all of the time in traffic jams when the road narrows.  The problem is that any slight event can cause the jam to turn into a stampede, with injuries and deaths.  I was amazed, and relieved, that this seemed not to happen in Cairo. Just a few weeks ago at least 104 pilgrims were killed and another 50 injured in a stampede of pilgrims in India.  Stampedes have killed people in a wide variety of venues--synagogues, theaters, meeting halls, train stations, air raid shelters, stadiums and, yes, Walmart (November 28, 2008).

And yes, this does relate to fluid mechanics--one model for traffic flow is based in river hydraulics!

Japan's biggest volcanic eruption in 50 years

Mount Kirishima/Shinmoedake eruption Jan. 26, 2011
From FNN-News.com

Mount Kirishima consists of several volcanoes covering an area about 20x30 km with more than 20 eruptive centers.  Shinmoedake, which last erupted in 1959, is approximately in the center. Eruptions have been recorded since 742, with strong eruptions in 788, 1716 and 1717 (Wiki). R. Imura published an "Eruptive history of the Kirishima volcano during the past 22,000 years" in Geographical Reports of Tokyo Metropolitan University, 1992. Geologic history older than 22,000 years is hidden by a very thick ignimbrite (ash) deposit from the eruption of the Aira caldera at that time.

Shinmoedake as seen from Takaharu Town Office
Early a.m. Jan. 27, 2011
Reuters/Takaharu Town Office/Handout
copyright status unknown

From 22-15 thousand years ago, five stratocones and two smaller volcanoes were formed.  The main products of the eruptions were lava flows.  Kirishima was fairly quiet between 15-7 thousand years ago, when eruptions then resumed.

Eruptions from this volcano appear to have become more explosive with the passage of time.  The eruption in 1959 was phreatic, that is, involving water.  It resulted in the formation of a 500 m long fissure on the west slope of Shinmoedake.  In 1991-1992 vigorous enough phreatic activity (steam explosions? not specified in the Imura article) caused authorities to ban climbing on it for about one and a half years.

Other posts about volcanoes on this blog are: Klyuchevskaya, Merapi, Merapi and map of major volcanoes of Indonesia, Santorini, Matua (volcanoes and atom bombs!), and  Etna.  A good blog on volcanoes is at the Smithsonian/USGS site.

Natural disasters in China, 2010

Mudslide in Zhouqu county,
northwest Gansu province, Aug. 9, 2010
Photo possibly from MSNBC

Today (January 27) China announced the allocation of 1.039 billion yuan ($157 million U.S. Dollars) to areas hit by natural disasters in 2010. This is in addition to 4.1 billion yuan ($617 million U.S. dollars) allocated in November to help the survivors of the disasters get through the winter.  A magnitude 7.1 earthquake hit Yushu killing 2200 people, and a mudslide in Zhouqu left 1700 people dead or missing. There are good posts on the mudslides and floods on Dave Petley's Landslide blog.

It has been estimated by the Disaster Emergency Management in China that natural disasters affect 200 million people every year, and that they are one restricting factor on social and economic development (reference here). These are typically floods and associated landslides, earthquakes and famines.  The deadliest flood, and possibly deadliest natural disaster, of all times were the 1931 floods in China, with estimated deaths ranging from 2,000,000 to 4,000,000.  The 1976 Tangshan earthquake killed between 242,419-779,000 people (I love the number of significant figures in that statistic!).  

Cyclone Tracy and "Santa Never Made it into Darwin"

Source unknown

The current floods in Queensland, Australia, are another in the extremes of fire and water that hit Australia (earlier post here). Cyclone Tracy struck Darwin, Australia, on Christmas Eve and Christmas Day, 1974.  It killed 71 people, destroyed over 70% of the buildings in Darwin, left another 20,000-25,000 people homeless, and caused over $800 Australian 1974 dollars damage. It spurred a priority to develop cyclone-proof buildings. Many of the survivors were evacuated to other towns and never returned to Darwin. The storm was an unusually compact cyclone, with gale-force winds extending less than 50 km from the center; the graphic on the right shows the relative sizes of Tracy (look hard for the small dot in the middle of Texas, right above the T in Tropical) and Super Typhoon Tip.  There's a good Wiki article on Cyclone Tracy here, so I'll not repeat the info.

Relative typhoon sizes.  Public domain, NOAA.

The event was so traumatic for Australians that it made it into the popular media.  Here's a link to a song describing the effects, sung by Bill (Cate) and Boyd (Robinson). It was a fund-raiser for the reconstruction effort.  Sometimes a scientific explanation can't compete!

Half Moon Bay surfer in critical condition after large wave strikes

January 23, 2011 big wave at Half Moon Bay
Photo by Nikki Brooks

http://www.latimes.com/news/

local/la-me-surfer-mavericks-20110124,0,4017331.story

A California surfer was caught in this big wave at Mavericks surfing area near Half Moon Bay, California.  He is in critical condition at Stanford Medical Center. Half Moon Bay is famous for its big, and dangerous, surf. On February 13, 2010, spectators crowded onto a narrow beach were hit by a wave estimated to be 50' in height. This wave was apparently caused by a combination of high tides and high surf. When the waves exceed 20' height, there is a contest held on short notice, with $150,000 prize money for competitors.  Just the day before the accident this weekend, the waves had been declared close, but not at, the 20' height. There is a web site dedicated to updating surfers on conditions here.

map of the sea floor near Mavericks (NOAA)
from this WWW site where you can find more discussion:
http://www.maverickssurf.com/wave/geog.php

What causes such big waves in Half Moon Bay? A combination of three factors: the waves generated by winter storms in the Pacific Ocean, the geology of the bay itself, and the complex topography of the underwater ocean bottom.  The geology of the area was described in 1965, by Warren Yasso who published an article in the Journal of Geology titled "Plan Geometry of Headland-Bay Beaches" (J. Geol. , v. 73 (5), pp. 702-714). A "headland bay" lies in the lee of a headland (obstruction) that causes waves to refract (bend) around it. The headland at Half Moon Bay is Pillar Point.  The beach formed in these settings has a characteristic concave shape that is caused by refraction, diffraction, and reflection of waves into the shadow zone of the headland.  To a good approximation, the concave shape of these beaches is given by a logarithmic spiral.  Half Moon Bay beach joins the beaches at Sandy Hook, NJ, and Drakes Beach and Limantour Spit along the Drakes Bay area, CA, in having this shape. The sea floor under this region is contorted because of the active tectonics and faulting that have occurred in this part of California. On the map above, dark blue is deep; red is shallow.  The center of the box is "Sail Rock", and the tan area to the northeast of it is Pillar point. The waves break in the area in the black box. The dominant wave direction through most of the year is from the northwest, and these waves do not generate large surf. However, sometimes during the winter, the strong storms in the north Pacific generate waves that come in from the west.  When they hit the shallow water at Sail Rock, they break over the bedrock reef just to the east of Sail Rock.  See here for more discussion, and an animation of the underwater topography.

To see a very different, and much gentler, surf posting on this blog, click here!

Boiling water turns to snow

from Water structure and Science, Martin Chaplin

Samantha Stewart, a Canadian woman, has become an internet hit with her experiment tossing boiling water into the frigid air of Saskatchewan (video)!  This is a popular activity, here being done at Mount Washington in 2007.  These features provide a chance to talk about my very favorite phase diagram!  Which is NOT the pressure-temperature diagram that we all learned in high-school and college (right diagram).

Here's an example of why the P-T diagram isn't helpful: Imagine that you have liquid water at P and T somewhere in the green field on this diagram, and that you lower the pressure while keeping temperature constant.  This would be a vertical path on the P-T diagram--for example, draw a vertical line down the 80 C mark.  The pressure changes continuously and, after the red line is crossed, all of the liquid water has turned to vapor.  But, a lot happens when your path crosses the red line--the liquid water boils.  Initially, just a few bubbles of vapor form, but the pressure and temperature can't change until all of the liquid has turned to vapor.  You are "stuck" on the red line until that happens.

T-S diagram for H2O: Excuse my lack of graphics skills!

In fluid dynamics, it's common to use a plot of temperature vs. entropy (T-S, left graph), which gives much more information about the state of a system for many problems in flow and thermodynamics.  On this diagram, you not only have the solid (ice) =S, liquid=L, and vapor =V) phases that you see on the P-T diagram, but you have the mixed phases: liquid + vapor (= boiling water or an aerosol, depending on the proportions of liquid and vapor) and solid+vapor (bubbly ice or snow). (Be careful, this diagram is only relevant to a pure H2O system, so you can't directly link it to snow in our atmosphere of nitrogen and other gases.) In the mixed phase regions, the horizontal lines are constant pressure, "isobars."

When processes happen very rapidly, they are adiabatic (meaning that no heat is transferred into or out of the system) and reversible.  Reversible processes have constant entropy, and so are represented by a vertical line in the T-S diagram.  I've illustrated two processes with the dashed vertical lines.  The dashed line with an arrow on the right is decompression of a cup of barely boiling water; the one on the left follows the decompression of strongly boiling water.  Both processes start at 212 F and end at -30 F, conditions reported for the Canadian and Mount Washington experiments. They start at 1 bar pressure (the horizontal line) and end at a very low vapor pressure, a fraction of a millibar. The amount of vapor formed is given by the "lever rule": it is the ratio of the dotted segment of the horizontal line to the total length.  You can see that if you approximate the "water tossing" as an adiabatic, isentropic experiment, it ends up as a mixture of cold vapor, and ice crystals (the snow).  There is much more vapor when strongly boiling water is tossed than when weakly boiling (or not even boiling at all) water is tossed, as you can see by the ratios of the arms in the lever rule. Presumably, the vapor that exists in boiling water expands and breaks the liquid water into small drops which crystallize rapidly to snow.  In theory and in equilibrium, vapor is formed even if the water initially has none, but equilibrium conditions may not be obtained in such rapid processes, so this may explain the observations on the video that cold water doesn't work as well as the very hot water.

The longest surf ride in the world!

Photo of surfers on undular tidal bore, Cook Inlet:
Scott Dickerson/www.SurfAlaska.net
Video is found by scrolling in here.

Thanks to Geology.com for finding this video of surfers catching a tidal bore in Cook Inlet, Alaska.  Wired magazine says that since January 13 it's had nearly 1,200,000 views! Fantastic waves at many scales.

A tidal bore occurs when the normal daily tides travel up a river or narrow inlet against the direction of river flow.  It is not, as commonly believed, a tsunami, and does not resemble a tsunami.  I saw the famous tidal bore in the Bay of Fundy a few years ago. This bore competes with Ungava Bay for the title of the highest tides in the world.  They appear to be tied at 16.8-17 m! During the 12.4 hour tidal period, 115 billion tonnes of water flow in and out of the bay. The size of the waves depends on the strength of the tides and while the one I saw was only a few inches high, the amount of water pouring into the Bay, and its inexorable march upstream, was phenomenal! Well worth the journey to get there.

Tidal bore in Cook Inlet. Photo from NOAA.
Public domain.

Tidal bores range in shape from the beautiful undular form see in the picture above to a breaking wave; the picture to the right shows a stronger tidal bore in Cook Inlet. Surfing on these waves, known as river surfing, has become a popular sport.

Why does natural gas explode?

Last night there was a terrible gas line explosion in Philadelphia, captured on screen by a bystander (see video here).  The line was apparently being repaired when the explosion occurred. One worker was killed and three others are in critical condition.

Natural gas is comprised mostly of methane, CH4, with up to 20% other hydrocarbons such as ethane, C2H6. Methane is notorious for causing explosions, and I covered some of the physics of explosion in a previous post. Gases are flammable only under certain conditions.  The "lower explosive limit (LEL)" is the composition of a mixture (with oxygen in most cases) that contains the smallest amount of methane possible for combustion, and the "upper explosive limit (UEL)" contains the highest.  Below and above these limits there is either too little methane (LEL), or too little oxygen (above the UEL).  There is a quantitative difference between the flammability limit and the explosive limit, but for all practical purposes these terms can be used interchangeably.

There are two types of combustion: deflagration, when the combustion zone (where reactions are taking place) travels at a velocity less than the speed of sound in the unreacted mixture, and detonation, where the combusion zone travels at a velocity greater than the speed of sound in the unreacted mixture.  An explosion occurs when the container in which the reaction takes place bursts.  Control of the gas and vapor concentrations is a major issue in occupational safety and health.

Saidmarch, Blackhawk, and Heart Mountain landslides

The Saidmareh landslide in Iran.

Geology.com is a great source of information for this blogger, and the image from the right, originally from NASA is from that site; it was also featured on Dave Petley's landslide site in 2009.  This landslide, which occurred about 10,000 years ago, is believed to be the largest yet identified on the surface of the earth.  About 20 cubic kilometers of limestone slid 1600 meters (a mile) vertically, spread across the Karkheh River and its valley. Some material traveled 14 kilometers. The slide dammed the Karkheh River, causing a landslide lake to form behind the earthen dam.  This lake eventually breached the dam.

Massive landslides are often triggered by earthquakes.  In the U.S., one of the most catastrophic occurred in 1959 in southwestern Montana.  An earthquake, M 7.3-7.5, caused a huge landslide that killed 28 people and cost $11 million 1959 USD in damage.  This slide blocked the Madison River, resulting in the creation of Quake Lake.  The earthquake is known as the Hebgen Lake earthquake.  Fearing that the lake would burst through the dam in a catastrophic flood, the Army Corps of Engineers almost immediately began to cut a channel into the slide, and within a month, water was flowing through this cut.  In contrast, the landslide dam blocking the Karkheh River in Iran lasted long enough that 150 meters of sediment accumulated at the bottom of the lake before the dam failed.

Landslides that travel long distances occur not only on Earth, but also on Venus, Mars, and Io. The conditions that permit such large, heavy masses to travel long distances have been, and are still, subjects of controversy.  The runouts exceed distances calculated from simple models in which friction is a retarding force.  One hypothesis, based on field observations of the base of the Blackhawk Landslide in California, is that there is a cushion of air that lubricates the base of the landslide.  Another suggestion is that internal vibrations could "fluidize" the rock debris, making the effective coefficient of friction much lower than would be characteristic of a sliding solid mass.

Within the U.S., the Heart Mountain landslide in northwestern Wyoming has a runout distance of about 50 km.  How it traveled so far has been a source of scientific controversy for decades.  In a recent paper, Goren et al. have proposed that a feedback between "shear heating, thermal pressurization, and thermal decomposition of carbonates" at the sliding interface accounts for the large runout distance. The model suggests that the sliding velocity was a few tens of meters per second to more than 100 m/s, and that it took only a few tens of minutes for the whole sliding event.

"Inland tsunami" in Toowoomba, Queensland, Australia; floods in Brazil; Sri Lanka

AP photo from here

More than 375 people are reported dead in floods and landslides in Brazil (note added on 1/17/11: over 600 deaths now reported). A million are reported homeless due to floods in Sri Lanka. Major floods have been occurring in Australia, building up for several months and culminating last night with the flooding of Brisbane, Australia's third-largest city. In spite of individual stories of courage and heroism, there have been at least 34 deaths there. The National Post in Canada reports "Horrific picture emerges of Australia flash floods", and that Brisbane resembled a "war zone" as the flood hit 30,000 properties.

Here and here are two excellent and scary videos of the Toowoomba flood:

The water rose so quickly in Toowoomba that the event has been described as an "inland tsumani".     Perhaps this poem--one verse from a nineteenth century Queensland droving ballad, "The Overlander"  about northern Queenslan--summarizes the setting:

"I come from the northern plains

Where girls and grass are scanty;

Where the creeks run dry or ten feet high,

And it's either drought or plenty."

The whole ballad is sung on this video.

A discussion of the role of La Nina and the North Atlantic Oscillation in these weather events is here. Although there is much speculation on the WWW about the role or implications of these events and climate change, there are also lessons to be learned by looking back 150 years at the history of this part of Queensland.  It is tragically like many, many other places in the world where humans have altered their landscapes. I excerpt the following history from this reference.

For more than a century, the Queensland government had a vision, and determination, to introduce farming into this region. Australian history in the 1800's is complex.  Queensland became an independent state in 1850, with a complex history of replacing pastoralism with farming and dairying--dairying being needed to sustain the farmers until crops were sold, or in case they failed.  In the 1887 a Department of Agriculture was established in Queensland, and by World War One, the region around Toowoomba was exporting grain.

In order to meet the demand for fencing, an enormous number of trees were felled, depleting the forest resource.  Reserves and parks were established in the headwaters, but tree-clearing and increasing stock numbers caused erosion on ridges and compaction of vegetation on floodplains. In the 1870's and 180's, residents of Toowoomba changed the forest into orchards, which caused the water table to rise and swamps to developed.  Drainage became a problem, and mixing of raw sewage and groundwater wells resulted in a series of typhoid epidemics in the 1870's and 1880's. This was corrected by civil engineering and introduction of sewage systems.

However, as has been observed around the world, the replacement of vegetation with urban roads and buildings increased the rate of runoff to the main river channels. Flash flooding became a common experience in the main towns. Thus, more than a century of history preceded the tragedy of this week.

More on flash flood dynamics in a later post.

Thunderstorms, antimatter, and asthma

Image produced by J. Dwyer/FIT, NASA, from this site.

What is antimatter? It is matter composed of antiparticles. Consider our normal particles, electrons and protons, that are the building blocks of normal matter. For example, one electron and one proton combine to become hydrogen. The anti-electron (called a positron) has the same mass as an electron, but the opposite electric charge--in this case, a positive charge. The antiproton would have the mass of a proton, but a negative charge. An antihydrogen atom then consists of an antiproton and an antielectron. Mixing of matter and antimatter results in the annihilation of both, with the production of high energy photons, that is, gamma rays and other particle-antiparticle pairs. Modern concepts of antimatter began in the 1920's when Paul Dirac realised that the Schrodinger wave equation predicted the possibility of antielectrons, which were then discovered by Carl Anderson in 1932. The study of antimatter has largely been the realm of astrophysicists and physicists, but they have been used in medical imaging in positron emission tomograpy (PET).

Scientists using the Fermi Gamma-ray Space Telescope have announced that they have detected beams of antimatter produced by thunderstorms on earth. This was announced by Michael Briggs, a of the Gamma-ray Burst Monitor (GBM) on January 11 at a meeting of the American Astronomical Society. NASA's Fermi spacecraft is designed to monitor gamma rays. The GBM monitors both outer space and the Earth below its orbit. When antimatter strikes Fermi and collides with a particle of normal matter, both particles are annhilated and the GBM detects the high energy gamma rayss produced. In most cases the gamma rays were detected above thunderstorms directly below the GBM, but a few were detected quite far away, as far as 2800 km in one case. Even though the storms were below Fermi's horizon, gamma rays that were produced by it travelled up the earth's magnetic field and struck the spacecraft. Further information is here.

When Googling for information about this phenomenon, I came across a 2008 study by a team of meteorologists and epidemiologists who had found that emergency room visits by asthematics increased in the days after a thunderstorm. They believe that the associated rain and wind break up pollens and spread them around over distances greater than the thunderstorm itself. I remember being surprised when I moved to Illinois that it was such a hotbed of allergies and asthma. What was there to be allergic to here but corn and soybeans? Well, there are other plants than corn and soybeans, and there are lots of thunderstorms!

Other blogs on this site related to storms and weather can be found here: super typhoon Megi,, winter storms in Europe and the Arctic Oscillation, football can be dangerous, and volcanoes and atom bombs.

Winter storm in southeast U.S. Freezing rain expected

Photo by SWK in Urbana, IL

Today a major storm is pounding the southeastern part of the U.S.  A major concern is that the abnormally cold temperatures that will persist through Tuesday will cause formation of ice and freezing rain that will bring down the power lines. Freezing rain is a hazard in the mid-latitude regions of the globe. Although major freezing rainstorms are relatively rare, they are amongst the most costly of hydrometeorological disasters. The Ice Storm of January 5-9, 1998 in Quebec and Ontario caused 25 deaths, left a million householders without power, caused nearly $US 3 billion in damages, and another $US 3 billion in short-term lost economic output and insurance claims. Some climate change scenarios predict that with warming, the amount of freezing rain will increase.  For example,  study of possible changes in south-central Canada during the winter predicts an increase of 85%, 60%, and 40% in northern Ontario, eastern Ontario (including Montreal, Quebec), and southern Ontario, respectively (Cheng, C.S. et al., Natural Hazards Earth System Science, 7, 71-87, 2007).

From Wiki, which adapted this figure
from two figures in Gay, David A and R.E. Davis,
Climate Research 3(1) 209-220, 1993

What is freezing rain? Under certain atmospheric conditions, raindrops become supercooled (cooled below the freezing point without turning to ice) while passing through a sub-freezing layer of air, and then freeze upon impact with cold objects on the surface.  The figure to the right shows conditions under which freezing rain occurs, and contrasts these conditions with those that produce snow, sleet and rain.  Freezing rain is a particular hazard to aircraft because it can add a significant amount of weight to a plane, and can resculpt the contours of the wings.  If an aircraft starts to accumulate freezing rain in flight, the safe and easy maneuver is to descend into warmer parts of the atmosphere. However, the conditions that produce freezing rain near the surface are such that the plane must climb to higher elevations to find warm air, a much more difficult maneuver if the plane has started to ice up.  In 1994, American Eagle Flight 4184 was in a holding pattern 65 miles southeast of Chicago's O'Hare airport.  Ice formed on the upper surface of its wings, causing the autopilot to disconnect and the pilots to lose control.  The plane crashed into a field, killing all 68 passengers and crew.  As a result of this accident, the airplane type (an ATR) was removed from service in most northern hubs prone to icing conditions, and  pilot operating procedures in icing conditions were substantially revised, including non-use of the autopilot under icing conditions.

China's stealth jet: How does it tie in to geology? !!

The purported Chinese stealth jet, J-20. Source of photo unknown.
Reported here.

News has been circulating on the WWW that China has tested a prototype stealth jet.  "Stealth" refers to a complex set of technologies used to make these jets relatively invisible to detection, not many of which are relevant to geologic processes! However, it is being said that the Chinese aircraft resembles the US F-22 supersonic jet, and supersonic flows are relevant to geology.

U.S. Navy photo of an Air Force F-22 Rapter,
June 22, 2009 in the Gulf of Alaska.

The F-22 is a supersonic aircraft (good Wiki summary here). Its roots date back to 1981 when the USAF developed a requirement for a new and superior fighter to replace the F-15 series. The production model was unveiled in April, 1997 and it first flew in September of that year.  There is a contract to Lockheed Martin for 183 jets by the end of 2011. Export of this plane is banned.Supersonic aircraft travel at Mach 1 or higher speeds.  The Mach number is the ratio of the speed of the aircraft to the speed of sound in the medium through which it is flying, in this case, air.  At room temperature, the speed of sound in air is about 343 m/s (about 760 miles per hour)--at high altitudes where it is colder, the sound speed would be slightly lower because it depends on the square root of the temperature.

From http://www.f-16.net/f-16_forum_viewtopic-t-8338.html

When an aircraft is flying at speeds much less than the speed of sound, it creates disturbances that spread out in all directions, like ripples on a pond.  The picture on the left of the graph on the left shows a limiting case when the jet is not moving at all. As the speed of the aircraft increases, the circles become distorted into ellipses, stretched away from the direction of motion, as shown in the middle picture.  When the jet reaches Mach 1, no disturbances radiate out in front of the aircraft--one major factor in making it stealthy.  No one on the ground hears it until it is "too late".

As the aircraft accelerates beyond Mach 1 (some aircraft can attain Mach 3-4) the circles of disturbance coalesce to form shock waves that stream off the nose and wings of the craft.  When you are on the ground and hear a "sonic boom", these shocks are sweeping across you.  The illustration on the right shows the nose and wing shocks from an F-22.  For stability, the craft cannot fly above speeds that would cause the shock from the nose to intersect the wings.  The shocks from the wing have a different shape than those from the nose because the angle of the wing is different than the angle of the nose, as illustrated in the graph on the right.

How does this tie into geology?  Some fluids, such as boiling water, bubbly magma, and dusty gases have very low sound speeds (here's a pdf of a paper that I published on this phenomenon).  The sound speed of boiling water can be as low as a few meters per second--this means that a fast track athlete could potentially run at speeds greater than Mach 1 if immersed in boiling water! Shock waves would be streaming off that runner like those in the photo above of the F-22!

Another way to envision the aircraft is from the pilot's view: he's not moving, but air is moving past him at Mach 1,2,3 or 4. The same applies to geologic situations.  Imagine that a fluid that has a low sound speed is flowing past an obstacle--a rock or a ridge, for example.  Shock waves will be generated around this obstacle that make the flow field very different from that created by low speed, subsonic fluids.  This fact has been under appreciated in general in the geologic community, and only over the past few decades have studies begun that include the possibility of supersonic flows.  I discussed one observation of shock waves earlier on this blog here.  Shock waves were observed by a number of people during the eruption at Eyjafjallajokul earlier this summer, for example, this You-Tube video.

Happy holidays!!

Thank you all who have logged on in the days since my last post! I'm on an adventure that turns out to have even fewer internet stops than I had anticipated, but have some fantastic geology to share when I return.

Meanwhile, everyone, I appreciate your interest in this site, and Happy New Years to all!

Winter storms in Europe and the Arctic Oscillation

From the Arctic Climatology and Meteorology Education Center
Figure there courtesy of J. Wallace, University of Washington

AO index from 1950 to present
from
National Weather Service
Climate Prediction Center

For several days now flights have been cancelled into and out of many of Europe's major airports.  London's Heathrow and Gatwick have been amongst the hardest hit, Paris Charles de Gaulle is canceling a quarter of the flights today, and Frankfurt is canceling at least 500 of a planned 1300 flights. Airlines are claiming that they haven't seen storms like this in 20-30 years.  What is going on?

Weather in Europe is strongly controlled by a natural phenomenon called the Arctic Oscillation. This is a pattern of pressures over the Arctic.  In a so-called "positive phase" (illustrated on the left of the figure at the upper right) the pressure over the polar region is low and higher pressure in the midlatitudes drives ocean storms toward the north.  In this phase, Alaska, Scotland and Scandinavia have wetter than normal weather, and the US west and the Mediterranean have drier conditions. Frigid winter air doesn't extend as far into North America as usual, which keeps much of the US east of the Rocky Mountains warmer than normal, but Greenland and Newfoundland are colder than usual. Since the 1970's the oscillation tended to be in this phase, which you can see by the dominance of red on the graph to the right.

In the "negative phase" there is relatively high pressure over the polar region and lower pressures in the midlatitudes, but the difference in the pressures are small, that is, the pressure systems are weak. We are now in a negative phase.  The Arctic is warmer than average, whereas parts of the midlatitudes are colder than normal.  The Arctic Oscillation especially affects patterns over Europe, and is the cause of the current blustery weather as well as that in December a year ago. Ironically, the Arctic Oscillation Index went strongly negative just about the time that the 2009  Copenhagen Climate Conference started, causing unexpectedly cold weather there!

For my European friends, stay warm and safe during these holidays!

Book Review: The Planet in a Pebble

Photo Oxford University Press

The Planet in a Pebble: A Journey into Earth’s Deep History

By Jan Zalasiewicz

Oxford University Press, 234 pp.

2010

ISBN 978-0-19-956970-0

$27.95 US

The Planet in a Pebble tells the story of the history of the earth as it can be inferred by a geologist thinking about a pebble. In this sense, the book is evocative of Thomas Huxley, who did the same in 1868 using a piece of chalk. Zalasiewicz, however, uses every method available in the 20^th and 21^st centuries, from the scale and style of field work to the microsopic detail provided by state-of-the art laboratory analyses now available to tell the story. In popular jargon, this is forensic geology. The intended audience appears to be the scientifically literate and interested. Given the state of science literacy in the U.S., this will, unfortunately, be a small audience here.

Zalasiewicz has studied the Welsh slate, a rock that had the “alas, reputation of being wet, grey, and monotonous,” for much of his career with the British Geological Survey, and is superbly qualified to tell this tale. He is the author of “The Earth After Us”, speculations on the state of the planet after humans are no longer a part of it. He is also a gifted writer who clearly loves the language. Two paragraphs from the prologue capture both the essence and the style of the book:

“It is just an ordinary pebble. One of millions that wash backwards and forwards on the world’s shorelines, or pile up on riverbanks or perhaps line your garden path. Yet that pebble, like its myriad kin, is a capsule of stories. There are countless stories packed tightly within that pebble, more tightly than sardines in the most ergonomic of tins.

The size of this story-capsule is deceptive. These stories are gigantic, and reach realms well beyond human experience, even beyond human imagination. They extend back to the Earth’s formation—and then yet farther back, to the births and deaths of ancient stars. Something of the Earth’s future, too, may be glimpsed beneath its smooth contours. Battle, murder, and sudden death are there, and ages of serenity too, and molecular sleights of hand that would make a magician gasp; there are extremes of cold in those stories. And also temperatures that far surpass the heart of our sun.”

Zalasiewicz says that humans love stories, are born storytellers, and he successfully tells a story here. Beginning with a chapter entitled “Stardust,” he introduces the concepts of atomic matter from which his pebble is built, and then moves on to briefly introduce the current structure of the earth’s interior before getting to the core of the book: minerals and sedimentary rocks. How were the Welsh slate pebbles actually formed and how do these pebbles relate to the “deep time” of geology that goes much further back in time than the age of the slate itself (410-570 million years)? He ends with speculations on the future of the pebble, and a nice suggested “further reading” list.

Along the way, he does a nice job of conveying the feeling about what the profession of geology is like, and the nature of the techniques that we use.

My criticisms of the book are truly minor. I was puzzled (as were several colleagues to whom I showed the book) why the front cover had brightly colored pink, grey and white rocks, perhaps even granites or sandstones(?) when the whole theme was the “wet, grey, and monotonous” shale. The back cover and chapter photos certainly show that there are plenty of beautiful grey rocks that could have been featured! If meant to challenge the reader to think about the story in every pebble, it’s too subtle, but perhaps it helps get people to pick up the book because it's more attractive than a collage of grey rocks? I also think that putting the List of Plates right in the front of the book immediately after the Table of Contents was a mistake. These captions are full of technical terms (graptolites, monazite, “tectonically thickened barrel-like mica”) that will discourage any casual reader who is not a geologist from turning more pages. A figure showing the terms used for the geologic time periods would have been helpful.

At this time, when there is such a need for science communication, Zalasiewicz’s contributions and talent are most welcome. I recommend this book not only for the well-told story of earth history, but also for the beautiful writing.

Followup on Pakistan floods

The  floods in Southern Pakistan before (left) last summers major flooding, during it (middle) and this month (right).
Photo collage originally from Modis instrument on NASA's Terra satellite.  This collage from Geology.com.

The NASA image of the September frame, with sites labeled for reference.

When I was first starting this blog, a crisis was developing near the border with China at Attabad, with the potential failure of a landslide dam (here's one blog that I wrote).  These floods that caused the crisis at Attabad moved like a wave from north to south, culminating with flooding near the delta at the bottom of the images (original, higher-quality images are available here). In these images, water ranges in color from light blue to navy; vegetation is bright green--even if it is sparse.  Bare land is beige to red. Clouds are pale green.  Here's another update as of 12/09/10.

The caption released with the images points out several places affected by the floods.  Around Sukkur on the inland side, an irrigation network had supported agriculture.  Floodwaters overwhelmed a dam north of here, creating a flood that inundated this area and dumped water into the preexisting Manchhar Lake.  There is no outlet for this lake, and so the flood waters have sat on the agricultural land for months. Even though the size of the lake has diminished during the autumn months, it is still larger than prior to the 2010 floods (compare the left and right images). Around the coast at Thatta, there is also evidence for lingering damage, with pockets of water remaining in areas which were dry in 2009. Such areas, if stagnant for long, become foci for disease.

The floods themselves were a disaster. The lingering effects such as the drowning of agricultural lands, disease, and dislocation of people from the flooded area are referred to as the "disaster within the disaster". We see how all of these can contribute to political instability in the events that are evolving in Haiti in the wake of the major earthquake there this year.

1859 Solar Superstorm

"The Northern Lights"
Frederick Church, American painter
painted in the 1960's,
perhaps inspired by the 1859 superstorm

I had an earlier post on a the current solar activity in the context of a concern of Newt Gingrich who has made it a political issue. NASA has an interesting blurb today that lays out some of the concerns, and this blog is a summary of that article which puts "The Great Solar Superstorm of 1859" in perspective of the events of the last half of the 20th century.  It includes the following collage of events from past descriptions of superstorms:

"She ran screaming down the street, unable to contain her terror as night was turned into hideous crimson daylight…communications networks failed and equipment burst into flame…a bustling city lost power, trapping thousands of people inside elevators…satellites malfunctioned and in an instant millions of people lost touch with critical services, doctors and children."

From the NASA report cited. Based
on the work of Smart et al.

The 1859 superstorm lasted for 10 days, and is deemed one of the most spectacular solar storms in the past 450 years.  The basis for saying this comes from work by Michael Smart and colleagues who discovered that nitrate concentrations in trapped gases in the Greenland and Antarctic ice crystals rise and fall with solar activity. The graph to the right shows atmospheric nitrate (NOx) abundances from Galileo's time to the present, with the 1859 event highlighted in red.  The article calls attention to the time period during which the satellite industry has based their estimates of "worst case" scenarios: the last part of the 20th century in which there were only two major events, August 4, 1972 and March 1991.  In contrast, since 1561, there have been 19 events more intense than these two, with an average (though nonuniform) interval of 23 years. "The current 40-7ear-0eriod has been the least productive in generating large [events] as far back as 1670 during the Maunder Minimum.  If you wanted to build satellites that endure the rigors of the space environment, Cycle 23 [our last one] and some of the severe storms during the last 50 years, were probably the wrong examples to use as a 'tall pole' for how bad things can get." (I need to update my NASA jargonese, never heard the 'tall pole' analogy before; wonder if goes with their newly discovered sense of drama (the collage above, and sunspot description mentioned below!).


Nevertheless, during Cycle 23, there were satellite outages and losses totaling nearly $3 billion, and commercial satellites collectively lost about 3 years of lifespan at an estimated eventual cost of tens of billions in lost profit.  There were also several near-misses with US electrical grid blackouts.  Those in Quebec who remember the day that the power grid went down in March in Quebec, or those of us who are here in a deep freeze in the midwest this December shudder (literally) at the thought of a length power outage.


If Cycle 24 (the one we have now begun) were to have such a storm, it would be close to sunspot maximum, sometime between 2010 and 2012, likely in March or September during the Equinoxes. If astronomers notice a "large, angry-looking" sunspot (when did NASA start writing poetically?!!) crossing the solar meridian, time to look out.  It is predicted that all satellites on the daylight side of Earth would be blacked out by an intense blast of X-rays and energetic particles.  The X-rays would destroy the D-layer and cause shortwave blackouts; ozone would be depleted by 5-10% causing a spike in skin cancer events.  Auroras would dazzle us around the world. Computer systems on earth would crash as the integrity of their binary information systems is compromised.  Satellite losses and malfunctions would run up to $20 billion losses, Defense Department satellites would be blinded in some ways, and GPS systems would report inaccurately. This would affect precision navigation, oil drilling, search and rescue, and military targeting. 150 million people in north America would suffer a blackout without any precedent. Components of transformers for which there are no replacements would be damaged and have to be manufactured overseas.  The daily cost could be $30 billion in lost salaries, spoiled food, and closures--a larger scale example of the danger of global interconnectedness that the Icelandic volcano Eyjafjallajokull showed us earlier this year.

Rogue wave damages cruise ship

Two days ago (12/07/2010) a cruise ship lost an engine after encountering "monster waves" near the South Shetland Islands north of the Antarctic peninsula. Two videos of the waves are here and here. The ship, The Clelia II, a 5-deck ship, is apparently safe and heading to Ushuia (Argentina), accompanied by an Argentinian naval vessel.  It departed Ushuia for the Antarctic on November 30 and was returning to port yesterday.  The ship is being reported as operated by Polar Cruises based in Bend, Oregon, but Polar Cruises has put out a press release that it neither owns nor operates the ship. It appears that the operator is Travel Dynamics International of New York.. The media is reporting that the ship is carrying 100 passengers and 60 crew members, but several pieces of information in the news conflict with more reliable sources.  According to the International Association of Antarctica Tour Operators, there were 88 passengers and 77 crew.  All of the passengers are from the US. This same ship had an accident Christmas 2009 when a stronger-than-anticipated current pushed it onto rocks at Petermann Island in the Antarctica Peninsula. The starboard propeller struck some rocks, resulting in the shutdown of the starboard engine and loss of electrical power aboard the ship. Damage was significant enough that expeditions were cancelled through mid-January, 2010.

SS Edmund Fitzgerald May, 1975

As can be seen on the video there were heavy seas, and reportedly 55 mph winds northeast of the Shetland Islands. Two ingredients contribute to the creation of rogue waves: strong winds and fast currents. Rogue waves are common in this area of the world because winds have a long interrupted stretch of ocean to blow on the sea surface and build up the waves. For centuries mariners told tales of monster waves up to 100 feet in height.  Mathematical probability theory, however, based on a Rayleigh distribution of wave heights led to conclusions that these waves were unlikely.  A concerted effort to document the waves, including satellite measurements and pressure records from buoys, has now shown that waves exceeding 100 feet are much more common than expected.

Rogue waves also occur on the Great Lakes, and are believed to have cause the sinking of the SS Edmund Fitzgerald in November, 1975. At the time, it was the largest ship (a freighter) on the Great Lakes. The ship sank so quickly that no distress signals were received. When it was located on the bottom later that month, it was found to have broken in two. One theory is that it was hit by the "Three Sisters", a name for the phenomenon that these rogue waves occur in sets (there is a hint of that in the videos above of the recent episode in the Antarctic).  "The Wreck of the Edmund Fitzgerald" was a 1976 hit song by Gordon Lightfoot.

Beautiful, beautiful volcanic picture!

Klyuchevskaya Volcano, December 4, 2010 as observed by the Advanced Land Imager (ALI) aboard Earth Observing-1 (EO-1) satellite. You can link to a high resolution image that covers a larger area here.

This is one of those "worth a thousand word" pictures.  Rarely have I seen a photo in which the atmosphere is so clear around a volcano, the winds are so calm, the lighting is so perfect, and the eruption so striking.  No scale is given for this particular photo, but it is one of a series that have been rising to nearly 8 km (26,000 feet) from Klyuchevskaya.  Perhaps even more striking than the plume is the beautiful collar of pileus clouds surrounding the higher flanks of the mountain. Pileus is the Latin word for "cap". They form when updrafts push up moist air from lower altitudes.  In rising, the air cools to its dew point, causing droplets to form and create the cloud. Pileus clouds often form over cumulus clouds, and over rising plumes themselves as shown in this post about the eruption of Sarychev Peak volcano.

Volcanic plumes have two parts. Near the vent from which they emerge, the ascent of the plume is driven by momentum.  Further away from the vent, the plume rises buoyantly, and at high elevations (not shown here), some plumes form an umbrella. My guess is that this one did not. Plumes transport volcanic ash.  Near the plume, the primary control on ash dispersal is the plume itself--it's momentum and buoyancy characteristics and, to some extent, its interaction with the atmosphere as air is entrained into the eruption column.  Further away from the plume, atmospheric structure and winds control the dispersal of ejecta.  An excellent reference on volcanic plume dynamics is "Physics of Explosive Volcanic Eruptions", Special Publication 145 of the Geological Society of London, edited by R.S.J. Sparks and J.S. Gilbert, 2002.

Cold Lahars Displacing People at Mount Merapi, Indonesia

Dredging in the Code River, Yogyakarta
Photo from here.

Eruptions at Mount Merapi, discussed here, here, and here before in this blog, produced ash and other debris that sits atop the mountain awaiting the monsoon rains. Those rains have arrived; the wet monsoon season in Indonesia lasts from November through March. For weeks muddy torrents have been flowing down from the mountain. On November 30 an apparently big one, reported to be up to 2 meters deep, arrived. According to the Nov. 30 edition of the JakartaGlobe, thousands of residents were forced to evacuate. These muddy flows of volcanic materials are termed "lahars", and they can be either hot or cold depending on the timing of the volcanic activity and the weather.

The lahars flow down the channel of the Code River, which flows through the center of Yogyakarta.  The river has been channelized to control the path of the lahars, a historic danger from Merapi. Sandbags up to 1 meter high help control the flows, but authorities have warned residents that these temporary levees will not contain the large flows that are likely to occur.  Surono, the head of the Volcanology and Geological Disaster Mitigation Agency (PVMBG) has warned that people should stay 300 meters away from the river.  Evacuation has been hindered by damage to roads and bridges, as well as by heavy traffic from people coming in to see the disaster.

An interesting side-bar mentioned in the DredgingToday.com article linked in the figure caption is that the dredging of the Code River has been hampered by the lack of heavy machinery.  However, people living near the river have been helping by manually carting material away.  Apparently it is well known that the volcanic mud is rich in nutrients, and a truck of this material is fetching 50-60 thousand Rp! (50,000 rupiahs convert to about $5.50 US.)

Cold winds, ancient life, and fossil preservation

Sea scorpion fossil from the Soom Shale,
South Africa, ~440 m.y. old
Credit: Univesity of Leicester, as reported
in ScienceDaily, 11/29/2010

Schematic diagram of possible origin of the Soom Shale
from Gabbott et al., 2010, ref. in text

The Soom Shale in South Africa is rich in well-preserved fossils, and geologists have wondered both why they were so abundant, and why they are so well-preserved. In some fossils, you see not only the bone structure, but muscles, gills and swimming paddles.  The answer appears to lie in the story of fierce winds pouring off an ancient glacier, presented in a paper in Geology this month (Gabbott, S.E. et al., Eolian input into the Late Ordovician postglacial Soom Shale, South Africa, Geology, 38(12), 1103-1106.)

During the Hirnantian glacial event, a 1-2 million year event at the end of the Ordovician period which extended from 490-433 million years ago, ice built up over the primitive continent of Gondwana.  his was a period of diverse marine invertebrates and early vertebrates. The ice sheet collapsed rapidly at the end of this time, producing a variety of glacial deposits,topped by the Soom Shale, a 10-15 m-thick black shale. The demise of the marine communities at the end of the Ordovician is widely viewed as the second most devastating extinction to marine life in the history of the earth, and the third largest of the five major extinctions. T Sarah Gabbott and colleagues analyzed thin sections of the shale and found that it contains coarse silt and fine sand in discrete layers (laminae) that are associated with organic material derived from plankton.  They concluded that the geologic setting resembled that found today on the McMurdo Ice Shelf in the Antarctic.  Dust, carried by fierce glacial winds, blew off the ice shelf and into the sea where it fell through the water column.  It carried nutrients that stimulated the production of phytoplankton, which sank to the bottom. In a press release, Gabbott speculated that not only did the nutrients fuel life, they preserved it well when the rotting carcusses sank into the cold, stagnant depths.  "A cold wind, here, was key to both life and death."

A few terms: plankton are the organisms that drift in the oceans, seas or bodies of fresh water.  There are three primary groups, defined according to their function: phytoplankton that use light for photosynthesis (a "producer"); zooplankton that feed on the phytoplankton (a "consumer"); and bacterioplankton (a "recycler"), which basically recycle the other two types of plankton.

Related posts on this blog: katabatic winds and icebergs,
katabatic winds and Mars.

Coal Mine Explosion in New Zealand

The entrance to the Pike River Coal mine.  Photo/NZPA
published by the nzherald.co.nz, Nov. 19, 2010

On November 19, 1 man was killed and 27 miners are missing due to an explosion in the Pike River coal mine on the south island of New Zealand.  The mine has been under development since the 1970's, and is excavating from the largest hard-coking coal deposit in New Zealand. It is in an environmentally sensitive area, and has been lauded as an exemplary development in a sensitive area.  The tunnel, seen at the left, goes nearly 2.5 km nearly horizontally into the mountain.  The trapped miners may only be a few hundred feet underground.

From this Wiki site

Dangers in coal mines arise from at least three factors: the presence of both methane and carbon dioxide gases, and coal dust.  In this particular area of New Zealand, active faults produce a seismic risk as well.  Other causes of accidents are rock bursts, collapse of natural or artificial pillars, flooding, malfunctioning of equipment, and improper use of explosives in the mining process.  Methane gas is nasty stuff: an asphyxiant, flammable and potentially explosive.

The combustion of methane, CH4, is exothermic.  When combined with two O2 molecules, it decomposes to form CO2 (gas) and 2 H2O (liquid) molecules, releasing 891 kJ of energy. It is both flammable and explosive.  When mixed with oxygen and nitrogen in air in certain mixtures (orange region on the ternary diagram to the right), it will explode. The blue line represents air. If there is less than about 5% methane in the mixture it is too lean to explode (the LEL point on the diagram), and if there is more than about 15%, it is too rich to explode (the UEL point).

The process of mining coal generates an enormous amount of coal dust.  When high concentrations of this are suspended in air, and there is even a small ignition source, the nearly instantaneous reaction of the fine coal particles with oxygen can produce an explosion.  The ignition source does not need to be a flame; it can be an electrostatic discharge, friction, or sparks from machinery.  Dust explosions are not restricted to coal mines, but have occurred around grain silos, flour mills, and metal works (aluminum, titanium).  They are intentionally part of thermobaric weapons; see my older post here.