Massive mudslide in Colorado on Sunday, Memorial Day weekend

The Sunday, May 24, Mesa County Mudslide. Dimensions
are uncertain, but at least 0.5 mile wide, 2-3 miles long, and
250 feet deep. Photo by Aaron Ontiveroz, Denver Post
as published here.

UPDATED: May 26 and May 28, 2014

Heavy rain again (after Oso and Afghanistan) appears to have triggered a massive mudslide, this time in the Grand Mesa country of Colorado. The location is 11 miles southeast of Collbran, about 40 miles east of Grand Junction. The area is remote, cell coverage is sparce to nonexistent, and news is just starting to break of this event. More than 3/4" of rain hit the area on Sunday.  Three men, locals who had gone into the area to investigate the possibility of a smaller slide when they noticed problems with their irrigation water, are missing.

Update May 26: Weather.com meteorologist Jon Erdman said that Grand Junction picked up 0.42 inches of rain on Sunday, and that higher totals atop Grand Mesa above the slide were likely Heavy rain is expected toward the end of the week and into the weekend, making the slide area still very dangerous.

Location of Collbran ("A") relative to Grand Junction

This slide (dimensions in figure caption) is significantly larger than the Oso, WA, landslide which measured about 1500 feet wide, 4400 feet long, and 30-70 feet deep. The area is on U.S. Forest Service and private land. No structures or major were involved. The sheriff has reported that the person who reported the slide heard a sound like a freight train, and that "the slide came down with so much force and velocity that it came to a hill and went up and over a hill and then came back down--a significant hill." The area remains unstable as of this writing (2:30 PDT, Monday).

Another photo of the mudslide taken by Aaron Ontiveroz
as found here.

The area where the landslide climbed a hill is at the
upper right of this image. It is at a sharp bend in
the path of the flow. Photo also by Aaron Ontiveroz,
Denver Post.

I couldn't find any references to previous slides in this area, but did find a 2013 paper entitled "Characteristics of Landslides in Western Colorado, USA", focused around the Somerset-McClure Pass area only about 50 km away (as the crow flies, a lot longer by any access roads as they are separated by the Grand Mesa National Forest and some rugged country.) The authors of this paper are N.R. Regmi, J.R. Giardino, and J.D. Vitek, and it is published in Landslides, on-line 05 June 2013. The Colorado Geological Survey also has an extensive website and inventory program that can be viewed here. It is painfully clear that western Colorado has major landslide problems.

Update 5/26: Geologist Jonathan White, with the Colorado Geological Survey, said that another slide seems inevitable because of the buildup of water in a depression created by the big slide. The depression that he's referring to may be (???) at the top of the slide in the lower photo. Water has been flowing into the depression already, but White says that it's impossible to tell when the next slide could occur--perhaps even years from now when people have forgotten the danger. The terrain is too unstable for any work to drain the water, and Jonathan Godt, a geologist with the USGS says that "practical engineering measures for things of this size are pretty limited."

Update, May 28: The last photo in this set shows the mobility of the flow as it climbed up and over the ridge in the upper right where it took a sharp right turn in the flow path. From a topo map of the area, it looks like the elevation of the headwall at its crest is roughly 9700 feet, and that the elevation where the slide began the right-angled turn is about 8000 feet. This drop of 1700 feet elevation occurred over about 1.5 miles. It looks like the topped a ridge that is a couple of hundred feet higher than the valley bottom (where it spilled over the ridge on the right side as viewed in the photo, left side when viewed from the flow direction). Since the slide was reported to be several hundred feet thick, it's not clear how much of this spill-over was due to the energy of the flow versus the thickness of it as it approached the ridge. Note the erosion line of the trees in the extreme upper right of the photo and how it appears to be close to the elevation of the top of the overtopped ridge. This suggests to me that the overtopping had a significant contribution just due to the huge thickness of the flow.

There is also a very unusual change in texture between the material that did not go up the hill (streamwise right) and the material on the proximal side of the hill (rough vs. smooth?), and I'm wondering if bigger particles in the flow got left behind as the more fluid finer-grained material climbed the hill? Did the flow climb the hill on its left side (toward the top of the photo) and then fall back toward the valley on its right side (the smooth area on the right side of the ridge)? Is it possible that the "slide" changed to a muddy flow at this point--certainly there is a change in the texture of the slide downstream from this area, as pointed out today by Dave Petley on his AGU landslide blog. Field observations will be needed to clarify many questions.

After making the first turn to the right, the material then turned to the left, spread out around and over a region of ridges (emanating from the hill on the streamwise right side of the flow in the middle of the photo), and eventually exited from the main channel, narrowly missing a developed site of some sort (natural gas, fracking facility??).  I'm not sure what this is, and the WWW is full of speculation. The elevation of the toe of the slide is about 7300 feet, making the total drop of the order of 2400'.

Camelopardalid meteor shower

In the lower right half of the image you can see the shape
of a giraffe and the location of the Camelopardalids meteor
shower tonight. Courtesy Science@NASA.

In the early hours of the morning May 24 (3-4 a.m. EDT and midnight and 1 a.m. PDT), a meteor shower from Comet 209P/LINEAR will dazzle observers with up to 1000 meteors per hour. This is a new shower, occurring five days before Comet 209P/LINEAR makes its closest approach to the earth (8 million kilometers) on May 29. The earth passes through the comets orbit, which is strewn with debris shed from the comet on previous passes. Amateur and professional observers are excited about the potential for this to be a "meteor storm", levels of 1,000 per hour, and many will be at telescopes or out on the lawn with pencil and paper counting them.

Plot of the Earth's path through the meteor shower
by Jeremie Vaubaillon.

Comet 209P/LINEAR was discovered on Feb. 3, 2004, by the Lincoln Near-Earth Asteroid Research (LINEAR) research project. It orbits around the sun with a period of roughly 5 years, with an aphelion out near Jupiter's orbit. As a result, calculations show that its orbit has been perturbed by the gravitational pull of Jupiter over the past few centuries, at least as far back as 1798. Most particles in the shower are smaller than a grain of sand and burn up high in the atmosphere.

Scientists are being cautious, predicting a few hundred meteors per hour to be on the safe side, but almost all of them express hope for the storm-level of 1000 per hour. Comet 209P/LINEAR is a small comet, and has in recent passes near the earth, a fairly low dust production. Observers in the United States and southern Canada are in the best position to see the shower.  The moon is a waning crescent, just four days from the dark new phase and will not be a hindrance.

Fred Whipple first developed the idea that comets were "dirty snowballs" orbiting the sun.The meteoroids are formed when a comet passes by the sun and some of the ice (water, methane, ammonia or other volatiles) sublimates, releasing the small silicate particles bound in it. The meteoroids spread out around the comet, eventually, after many passes by the sun, filling in the entire orbit.

Here is a link to Mikhail Maslov's website on the 2014 meteor shower, and here is a post by Robert Lunsford.

Afghanistan landslide of May 2, 2014

The Badakhshan landslide, showing its extreme mobility
Photo by Blal Sarwary as posted on Dave Petley's Landslide Blog
Links to sources are in adjacent text.

Our thoughts and condolences are with the survivors of the devastating landslide in Afghanistan.

On his Landslide Blog, David Petley has drawn from the Twitter feed of Bilal Sarwary, a BBC reporter on the spot where the landslide occurred in the Argo District of Badakhshan Province in Northeast Afghanistan was a failure in deposits of windblown sand (loess) after a period of heavy rainfall and flooding. With no hope of recovering the bodies of victims, Afghanistan has declared the site a mass grave and dedicated Sunday as a day of national morning.

While Petley conservatively says that "is now believed to have killed at least 350 people," the news media are reporting as many as 2000 deaths. Even the conservative value makes it the worst landslide to date in 2014, and the death toll is bound to increase as reports of missing people come in. There are about 4,000 survivors in need of care. The landslide is believed to have occurred in two phases, separated by enough time that people from adjacent villages had arrived to help with rescue efforts, only to be caught by the second landslide. Note that the Oso landslide in the U.S. two months ago also had two phases, but these were separated only by about 4 minutes.

Location of the landslide
From Cnn.com here

Petley based his conclusion that the landslide had occurred in loess on the high mobility of the landslide shown in the photo above, and the observation that there are no large boulders visible in the photo, an indication that the sediments were probably wind-laid. Landslides in loess are not unknown in this part of the world, though much more reported from China than Afghanistan. Loess covers huge areas of the world (see map), including some that are prone to large earthquakes (up to M8.5), such as this part of Asia. Loess covers 6.6% of the total area of China. In the middle part of the Yellow River in China, it can be 1000' thick. Chinese scientists have pioneered may of the studies of loess failure.

Map of location of loess deposits from here.

Loess was deposited during the Pleistocene by winds blowing across deposits of the receding glaciers. The climate was dry and, in many areas of the world, such as China and Afghanistan, has remained relatively arid since the loess was accumulated.  It is highly porous and has a weak cohesion, giving it rather unusual geological engineering properties.* It can contain up to 20% water in so-called "macropores", see photo. The mosaic structure of loess gives it strength, but the existence of macropores makes the strength vulnerable under seismic shaking or heavy rains. When loess fails due to heavy rains (or over-irrigation), it is because the pores fill with water, destroying the strength of the soils. However, even relatively dry loess has been known to fail.

Macropores in loess, Tianshui, Gansu Province
from the Zhang reference cited at *

There are a number of ways in which landslides can be triggered in loess areas. Zhou et al. (2002)** have classified loess landslides according to three "indicators": (1) the landslide material; (2) the position of the surface along which the slide moves; and (3) the mechanism of movement. Landslide materials can be either loess alone, or loess and underlying soil/rock, such as laterite, which is common in this part of the world. The development surface can be solely within the loess, or within the loess and underlying soil/rocks. The mechanism of movement can be slow gliding, or "collapsing-gliding." They point out that (in China, but I'm assuming that this applies to Afghanistan), landslides occur in (a) the rainy seasons of July, August and September, and (b) the ice melting period of March, April and May. This Afghanistan slide, if triggered by heavy rains, has occurred early compared to to the (Chinese) rainy season.

Water affects/causes landslides in three different ways: rainfall, surface water, and ground water. Both rainfall and surface runoff can increase the water content of a hillslope, and even saturate it. When saturated, e.g., below the water table, the cohesive force of the soil and the frictional force of layers within it can greatly decrease. Surface water also erodes the topography, particularly in tectonically active areas of the world. This leads to unstable, steep slopes prone to landsliding. Changes in groundwater affect the mechanical characteristics of soil. For example, when water content of soil increase up to 35%, shear-resistance decreases by 60% (Zhou et al., page 160). Ground water can also dissolve components of the soil, changing its composition and strength. 

Zhou et al** point out the potentially large influence of humans on inducing landslides. Remembering that this article was written in 2002, so that the statistics are not current, they report that in the 20 years preceding their report, population had reached 81.49 million, accounting for 7.8% of the nation's population. With this increase of population, "irrational human activities" such as excavating foothills, filling hillsides, and over-cultivating accelerated natural disasters. Because industry is relatively sparse in these loess areas, the output of industry and agriculture was below the national average, accounting for 6% of that of the nation. These areas tend to be poor, and frequent natural disasters "are major factors hindering the social and economic development of [the] loess area." On the borders of the loess plateau, flat ground is rare and slopes are universally leveled to build houses, and many people live in cave-houses cut into the slopes. All of these activities reduce the support at the bottom of the slope and decrease its stability. Vegetation, that normally stabilizes a slope, has been heavily impacted since the 1950's by deforestation. 

ASIDE: Although there appears not to have been an earthquake that triggered the Afghanistan landslide, it is worth keeping in mind that this huge region in Asia is subject to major earthquakes, which commonly trigger landslides if they are greater than M6, and wet weather.

COMMENT ADDED APRIL 6: John SanFilipo has commented that "There was a small (?) quake just west of the slide area near Rostaq reported on 12 April. Thanks, John! It will be interesting to see if anyone looks for a cause and effect.

On December 16, 1920, the M7.8 Haiyuan earthquake (also called the 1920 Gansu earthquake and estimated by some to have been as high as M8.7) killed at least 100,000 people, probably double this number according to the USGS. A Chinese paper in existence at the time Ningxia Daily, reported 240,000 killed. Strong trembling occurred for 10 minutes. Reportedly, 500,000 houses and cave dwellings collapsed.* The shaking occurred over an area of about 50,000 square kilometers, most of which is covered by loess. The landslides triggered by the earthquake blocked rivers and buried villages and farmlands.

There are several prominent consequences of earthquakes. (1) Fissures are produced both near the fault and far away from it. Near the fault, the fissures are primarily related to tectonic deformation and are spread on both sides of the fault. However, in zones of weak shaking far away from the fault (all the way through much of the loess region in China) fissures can be formed by subsidence in the loess caused by the loss of strength of the loess when it is shaken (liquefaction). (2) Landslides occurred in three types of areas in the Haiyuan quake: (1) near or in the high intensity shaking zone. However, because the soil cover was thin in this region, the landslides were quite small. (2) In an area of moderate shaking, more than 1000 sq. km. in area, there were 650 landslides reported (see the Zhang ref below), and 41 of them dammed rivers to form so-called "barrier" or "quake" lakes. These slides were big because the area was hilly and covered with loess ranging from 20-50 m (66-165') in thickness. (3) More distal regions where the damage caused by the landslides was more severe than that caused by the shaking of the quake itself. This area covered another 1000 sq. km.



*Zhang, Zhenzhong, Geological disasters in loess areas during the 1920 Haiyuan earthquake, China, GeoJournal, 36 (2/3) 269-274, 1995.

Zhou, Jin-xing, Zhu Chun-yun, Zheng Jing-ming, Wang Xiao-hui, Liu Zhou-hong, Landslide disaster in the loess area of China, Journal of Forestry Research 13(2), 157-161, 2002.