The mysterious "sailing stones" of Death Valley

Credits as above. Picture grabbed from ScienceDaily.com.

How can a rock weight several hundred pounds move hundreds of meters across a "dry lake"?  And, why do they move in tandem? One of the early pioneers in solving this mystery was Robert Sharp* of Caltech, and many others have speculated about this problem. Sharp monitored stones over a period of seven years stretching from 1968-1974, and concluded that movement was related to wet stormy weather. Sharp and Carey documented a greatest cumulative movement of 262 m, and "greatest single-episode movement, of 201 m. These were of a small 250 g stone, but other moved stones weighed as much as 25 kg. They concluded that movement "most likely occurs within one to several days after playa wetting, and velocities on the order of 0.5 to 1 m/sec are inferred from track characteristics." Sharp and Carey reported eyewitness accounts of ice sheets containing frozen stones being propelled by wind on other southern California playas, and inferred that the stone tracks at Racetrack were made in this way. However, there were observations that led them to conclude that the stones could not move within extensive ice sheets: they moved out of an encirclement of iron stakes that Sharp and Carey had placed and their spacing changed during movement.

Stationary rocks (blue arrows) and rock moving from left to right (red arrow)

The team used quarried rocks,
one shown here with its
GPS unit

Now, the process has actually been observed by a team led by Richard Norris of Scripps Institute of Oceanography.** In what one of the co-authors, Ralph Lorenz, described as potentially the most boring experiment ever, the scientists outfitted 15 rocks with motion-activated GPS sensors and placed them on the playa to await movement. Only two years into the project, not only did the rocks move, but Norris and Norris were there at the time. When they arrived in December 2013, there seven centimeters (3") of water on the playa, and they concluded that not only must water be present, but it must be deep enough to form "floating ice" during cold winter nights, but shallow enough to leave at least part of the rocks exposed. Panes of ice form during the night, and on sunny days the ice can begin to melt and break up into panels that float across the water if there is wind. These panels actually push the rocks in front of them. The wind speeds were about 3-5 meters/second (10 mph), and the ice that moved was about 1/4" thick.  These speeds are much lower than inferred from track characteristics by Sharp and Carey. The rocks moved at 2-6 meters a minute, and moved for a few seconds to 16 minutes. The rock trails formed under the ice, and became visible only when the water underlying the ice is blown away by winds.

Floating ice moves around the playa under the influence of winds. When it encounters rocks, it may pile up on the upstream side, increasing the effective cross-sectional area of the rocks to both upstream ice and water and thus facilitating movement. On the other hand, sometimes the ice fragments upon encountering a rock. Norris and Norris suspect that this phenomenon might explain the Sharp and Carey observation of the corral behavior: the rock that didn't move out of the corral was just downstream of a stake that may have shattered the ice. Stones with low profiles might be submerged beneath the ice, some rocks may be too big for the available forces under some wind conditions, and others may not totally or partially encounter ice.

But, the researchers concluded, the mystery may not be completely solved: they didn't get to see the really big ones move.

The authors also point out that the sliding rocks are not unique to Racetrack Playa or even the U.S. Ice-driven rock trails are observed on the bottom of Great Slave Lake in northern Canada and on the shores of the Baltic Sea. The mechanism may apply to rock trails on dry lake surfaces in Spain and South Africa where the lakes are at high elevation and exposed to cold winters.

*Robert P. Sharp and Dwight L. Carey, Sliding stones, Racetrack Playa, California, GSA Bulletin, 87(12), 1704-1717.

**Richard D. Norris, James M. Norris, Ralph D. Lorenz, Jib Ray, Brian Jackson, Sliding rocks on Racetrack Playa, Death Valley National Park: First observation of rocks in motion. PloS ONE, 2014; 9(8) e105948 DOI:10.1371/journal.pone.0105948 link to article is here

South Napa Earthquake today, M 6.0-6.1--geologic context

Building destroyed in Napa. Photo by Justin Sullivan,
Getty Images as published on www.sfgate.com here

UPDATE AUGUST 25: Greg Braswell, as noted in his comment, has published images of the damage and an iso-damage map. They can be found at:

https://plus.google.com/photos/111007793583080982677/albums/6051216644873549681

and

https://mapsengine.google.com/map/edit?mid=zv4bNVwln6qk.kOPvmSymk_d8

Headlines this morning announced that a M6.0 (or 6.1, conflicting reports) earthquake at 3:20 a.m. awoke people around the area of Napa, California, north of San Francisco.  Dozens of people are injured, four homes in a mobile park burned, and damage to buildings in downtown Napa appears extensive. The quake is the largest in the Bay Area since the 1989 Loma Prieta earthquake.

        Here's a bit of context that I found in an on-line technical report authored by John R. Wesling and Kathryn L. Hanson, 2008 (reference at the end of this post). Here is also a link to the USGS earthquake event page.

Map of the five sections of the fault defined by Wesling
and Hanson (Figure 3 from the cited report)

        Napa Valley is a large valley that trends to the northwest. It extends from Calistoga to the southern part of Napa and includes much of the core of the city. The valley is filled with Quaternary alluvial and fluvial deposits from the Napa River system, and earthquake damage in Napa can be especially severe during earthquakes because of shaking of these deposits. The West Napa Fault and its branches were first mapped by Weaver (1949), and subsequent work extended from the 1970's into the 1990's (references in the article cited). This early work reported that the fault and its branches extend 30-35 km along the western margin of the Valley; the Wesling and Hanson report suggests that the fault is 57 km long, extending from Carquinez Strait northwest toward St. Helena. The orientation and geomorphic expression are consistent with the West Napa fault being dominantly a right-lateral slip fault, with some compression that allows development of the nearby mountain ranges. The West Napa fault is one of a series of fairly short faults that include the Franklin and Sothampton faults. These faults lie between the Hayward-Rodgers Creek Fault zone (west) and the Calavaras-Concord-Green Valley fault zone (east).

          Wesling and Hanson divided the fault into five reaches based on geomorphic expression, terrain traversed, and availability and quality of data. These branches are: St. Helena-Dry Creek; Yountville-North Napa; North Napa-Napa River; Napa River-American Canyon; and American Canyon-Carquinez Strait. The USGS is reporting that the earthquake struck 3 miles northwest of American Canyon, and placed the epicenter between 6 miles southwest of Napa, toward Vallejo (see adjacent map). According to the map above, this would place the epicenter on the Napa-River-American Canyon fault toward the northern end or, possibly, the southern end of the North Napa-Napa River branch, depending on where the reference point within Napa city is located.

            No historical earthquakes larger than M6.0 have been associated with the West Napa fault, although the M5.0 Mount Veeder earthquake ("Yountville earthquake") in 2000 may have been linked to it. This earlier earthquake was centered about 5 km west of the West Napa fault, and caused considerable damage in Napa.


Reference: "Mapping of the West Napa Fault Zone for Input into the Northern California Quaternary Fault Database," by John R. Wesling and Kathryn L. Hanson, 2008.

Bardarbunga volcano, Iceland, rumbling!

UPDATE: August 23, 2014

__________________________________________

Chaotic ice in Vatnajokull over Bardarbunga
Image from the Smithsonian site here

UPDATE: UPDATE: August 23, 2014. Here is a link to the Icelandic Met Office Bardarbunga information. New information is constantly added at the top of the article.  At 14:10 (Icelandic time), a small eruption of lava was detected under the Dyngjujokull glacier (east of Bardarbunga). Data from radar and web-cams (see this link, for example), have shown no signs of surface activity breaking through the 150-400 meter thick ice. However, the aviation code has been changed from orange to red, though no Icelandic airports have yet been closed. The Icelandic Met office estimates that it could be up to 20 hours before lava breaks through the ice, if it even does. The eruption could remain subglacial. Earthquake activity has continued since August 16. Flooding remains a possibility, with the bridge shown in the picture potentially at risk on the circum-Iceland road.

Earlier in the day, scientists reported that seismic activity indicated that a dyke was propagation as much as 5 miles to the north. On August 21, the dyke was reported to be 25 km long at a depth of 5-10 km. GPS data show that magma is moving.


ORIGINAL POST:

Earlier in the day, scientists reported that seismic activity indicated that a dyke was propagation as much as 5 miles to the north. On August 21, the dyke was reported to be 25 km long at a depth of 5-10 km. GPS data show that magma is moving.


Headlines are starting to appear about seismic activity under Bardarbunga volcano, which lies under Vatnajokull in Iceland, but with frustratingly little information as they hark back on the sensationalism of airplane flights cancelled when Eyjafjallajokull erupted a few years ago. More than 300 people in the region have been evacuated as a precaution. Flooding is a possibility.

 Rather than paraphrasing, here are extracts from the Smithsonian volcano report:

13 August-19 August 2014 

During 13-19 August the Icelandic Met Office reported increased seismic activity at Bárdarbunga volcano. On 16 August more than 200 earthquakes were reported under the NW Vatnajökull ice cap, and GPS stations have shown an increasing signal upward and away from the volcano since early June 2014. On 16 August the Aviation Color code was increased to Yellow. On 18 August the Icelandic Met Office reported an earthquake swarm to the E and another to the N of Bárdarbunga. A M4 earthquake was recorded that was the strongest in the region since 1996. By 18 August there had been 2,600 earthquakes detected at the volcano; earthquake locations from N and E swarms had been migrating NE, but in the evening activity of the N swarm had decreased significantly. That same day the Aviation Color code was raised to Orange. 

Credit: Reuters, as published in bbc.com here

The large central volcano of Bárdarbunga lies beneath the NW part of the Vatnajökull icecap, NW of Grímsvötn volcano, and contains a subglacial 700-m-deep caldera. Related fissure systems include the Veidivötn and Trollagigar fissures, which extend about 100 km SW to near Torfajökull volcano and 50 km NE to near Askja volcano, respectively. Voluminous fissure eruptions, including one at Thjorsarhraun, which produced the largest known Holocene lava flow on Earth with a volume of more than 21 cu km, have occurred throughout the Holocene into historical time from the Veidivötn fissure system. The last major eruption of Veidivötn, in 1477, also produced a large tephra deposit. The subglacial Loki-Fögrufjöll volcanic system located SW of Bárdarbunga volcano is also part of the Bárdarbunga volcanic system and contains two subglacial ridges extending from the largely subglacial Hamarinn central volcano; the Loki ridge trends to the NE and the Fögrufjöll ridge to the SW. Jökulhlaups (glacier-outburst floods) from eruptions at Bárdarbunga potentially affect drainages in all directions.

The Veidivötn fissure system, which extends 100 km SW from Bárdarbunga volcano, has been the source of major eruptions during the Holocene. A large, dominantly explosive eruption at about 870 AD from the Vatnaöldur crater row, which extends diagonally across the center of the photo, deposited tephra over much of southern Iceland. The Vatnaöldur eruption originated from a 42-km-long fissure and produced 3.3 cu km of tephra at the time of the settlement of Iceland, forming the the Landnam (Settlement) tephra layer. 

The subglacial Loki-Fögrufjöll volcanic system...glacial ridges extending from the largely subglacial Hamarinn central volcano; the Loki ridge trends to the NE and the Fögrufjöll ridge, seen here, extends to the SW. 

Weather extremes, atmospheric rivers and Japanese fire bombs

A shot-down Japanese fire balloon
reinflated by the US
File uploaded by Bkwillwm to
Wikipedia, public domain

     In my book, "The Dynamics of Disaster" (Norton Press, 2013), I discuss the big "rivers in the sky"--our jet streams.  These atmospheric rivers were discovered in the 1920s by Wasaburo Ooishi, a Japanese meteorologist studying the dynamics of the atmosphere near Mount Fuji. To quote my book: The Japanese "were able to turn their knowledge of the jet streams to their advantage during the war by launching balloon attacks on the US, sending 9,000 "fire balloons" aloft to travel thousands of miles east. Some 300 made it to US soil, and six people died when a family approached one and it exploded. (These were the only known deaths by enemy action on continental US soil during World War II.)"
        In a new study by Dim Coumou and a team from Potsdam Institute for Climate Impact Research published August 11 in the Proceedings of the U.S. National Academy of Sciences (ref. below), Coumou points out that the large number of very high-impact extreme weather events over the past decades has seemed out of proportion to the rate of warming of the atmosphere caused by increased CO2. The authors rely on, and quote, an earlier paper in PNAS by Petoukhov, et al. (of the same institute) reporting the same thing: the frequency of these extreme events over the past decade is such that it is unlikely to be just a "stochastic mechanism of extremes."
        And, here's where the Japanese discovery of the jet stream becomes relevant, because it's in the jet stream that the changing flow patterns are driving the weather extremes.

From the cited PNAS article. Shows the increase in so-called "boreal summer weather extremes."

        Again, quoting from my book: "Flowing at the top of the troposphere, the jets have variable elevations between 12,000 and 80,000 feet...[They] can be several hundred miles wide and 1-2 miles deep, and they can flow at speeds of up to 400 mph. Jet stream winds generally flow from west to east, but they have a loopy structure and flow in various directions, even "backward," from east to west, in some segments. The looniness, known as a Rossby wave, has a wavelength of about 1,800-2,400 miles and arises primarily because the Coriolis effect has different strengths at different latitudes. The jets can split apart, re-join, reverse, or simply stop.When the Rossby waves move to the north, they suck warm air northward, e.g., from the tropics into Europe, Russia, or the US. They do the reverse when they move south, transporting cold air from the Arctic to the south.  " I then go on to explain how the position of the jet stream and the Rossby waves influenced the position of Hurricane Sandy in October 2012.
       Now back to the research of Coumou and his team: According to the theory advanced in the article (based on analysis of meteorological conditions from 1979 to 2012), there are resonances in the atmosphere that trap the Rossby waves into certain configurations for long periods of time. Thus, a heat wave that would not be dangerous if it were a few days long, becomes extreme when its duration increases. (The paper is limited to analysis of the Northern Hemisphere.)
     The speed at which a wave travels along the jet stream (the "phase speed")  is, in one approximation, directly proportional to the mean zonal wind speed. To first order, synoptic waves with a wave number (k) equal to 6-8 travel at this speed. The zonal mean wind speed changes with season, being less in the summer. Because the zonal mean wind speed is lower in the summertime, the phase speed is also lower because of this direct proportionality. In fact, in the "boreal summer"--July, August--the phase speed can be close to zero (the waves are quasi-stationary, especially for wave number 6) or even negative (that is, the waves would travel to the west instead of the east). This weakening of the zonal wind speed and, hence, the wave speed is one mechanism explored. Free-traveling waves are simply slowed down or stopped. If the waves are stationary, then the troughs and ridges of the Rossby waves are stationary, setting in the northerly or southerly flow of air for long periods.
        The second mechanism is  the amplification of quasi-stationary waves by resonance between free and forced waves in the midlatitudes. Looking at the Petoukhov et al paper, the quasi resonance hypothesis is as follows. (1) Generally, the large-scale atmospheric circulation at mid latitudes is characterized by traveling Rossby waves with zonal wave numbers (k) equal to or greater than 6 propagating in the longitudinal direction at a phase speed of c~6-12 m/s as discussed in the paragraph above. (2) The circulation is also characterized by quasi stationary planetary-scale Rossby waves with c~0, frequency w~0, and various zonal wave numbers m that develop in response to orographic obstacles or weather sources and sinks, that is, to "conditions in the atmosphere that differ from place to place on the earth. Their hypothesis is that during the extreme summer events, persistent wave structures with high amplitudes evolved and made an unusually large contributions that the usually weak midlatitude response to the thermal and orographic sinks was strongly magnified at wave numbers 6,7 and 8.
     They assert that the apparent cluster of resonance events observed in their data set (see their figure reproduced above) is due to an increased wave 7 and 8 resonances, and that furthermore, these resonances high in the atmosphere are coupled to persistent weather patterns at the surface, and thus the extreme weather events. The changes observed are statistically significant at the 95% confidence level.
        The theory and data (from 1979-2012) suggest that because of warming in the Arctic, temperature differences between the Arctic and tropics are decreasing. Temperature differences drive the atmospheric circulation patterns, and changes in these differences (the temperature "gradients") are causing the atmospheric circulation patterns to change. Although much more detailed work and analyses needs to be done, their tentative projection (Figure 7) of conditions a century away shows t"similarities with the recently observed anomalies). According to RCP8.5 climate model (one in which we don't curb our CI2 emissions very much), the July-August thermal gradients will increase northward of 50N and decrease southward of 50N, leading to strengthening of the sub polar jet and weakening of the subtropical jet.


**I have used the report in ScienceDaily.com for parts of this post: http://www.sciencedaily.com/releases/2014/08/140811170106.htm

The abstract for the Coumou PNAS article is here and the full text is here.

The PNAS Petoukhov et al. article referenced is here.

Methane outbursts due to melting permafrost in Siberia: the Yamal crater

Image from the Washington Post here

Update: Of interest may be Alan Weisman's August 12, 2014 article "Why the Earth is farting." Also, see reader comment.

Several months ago, a photo of a crater discovered by a helicopter crew  went viral. It is located in the Yamal Peninsula in Siberia, a desolate spit of land. The crater was variously reported to be 100- 200 feet in diameter. In the July 31 issue of Nature, highlighted in the Washington Post article referenced in the adjacent figure caption, the discovery of two nearby craters is reported in the Washington Post article. The article contains an excellent video taken from a helicopter showing the crater walls actively crumbling. A camera has been lowered to 50 m, and it showed a pool of water at a depth of 70 meters, so the crater extends below 70 m.

Image from Washington Post here

Russian researcher Andrei Plekhanov led an expedition to the crater. He found that near the bottom of the crater (at approximately 50 m depth) air contained concentrations of methane up to 9.6%. That is to be compared to the normal concentration of methane in air--0.000179%. They believe that the abnormally hot summers in Yamai in 2012 and 2013 caused permafrost to thaw. Under the permafrost, usually at depths of 100 meters, methane clathrates are stable. Over the past 20 years, permafrost at a depth of 20 meters has warmed by about 2 C according to the article, quoting Hans-Wolfgang Hubberten of the Alfred Wegener Institute in Potsdam, Germany. Hubberten speculates that a thick layer of ice overlying the clathrates allowed gas pressure to increase until it was great enough to blow out in an explosive burst, forming the crater with rubbly ejecta strewn around it.
     The development of more craters could pose a danger to villages of local reindeer herders, and the craters are only 30 km from a large gas field, the Bovanenkovskoye gas field. A blowout in the gas field cold be very dangerous.

August 2 Major Landslide in Nepal blocks only route out to the North

Image of the landslide from Ekantipur. This appears to be
a view on the upstream side, with the water from the impounded
river flowing to the right and encroaching on the toe of the slide.
Image from Dave Petley's blog post of August 2, 2014.On

On the night of August 1-2, a large landslide occurred along the Sunkoshi River in northern Nepal, damming the river and creating an urgent crisis. I'm not going to follow this event because Dave Petley's landslide blog will be providing excellent coverage. It is the peak of the monsoon season and so the impounded lake behind the landslide is likely growing fast and, Dave believes, may already be overtopping the dam. It also appears that the dam is in fine-grained materials and so the likelyhood of a breach is high. The valley downstream is heavily populated (evacuation has apparently already begun) and the main road from Nepal into China is blocked. The highway, however, does provide a route to bring in heavy machinery and crews to work on excavating a channel through the slide.