Thursday, August 31, 2017

Massive Martian Landslide found in Shalbatana Vallis using Google Earth "Mars"

Shalbatana Vallis Landslide (looking south). Image from Google Earth "Mars" 
The Shalbatana Vallis canyon is nearly 800 feet deeper than the Grand Canyon. A huge section involving seven and a half miles (11.5 km) of the eastern flank of this canyon failed in a massive landslide that involves a total of 66 square miles (171 square km). What is most impressive is that the toe of the landslide liquefied and flowed several miles across the canyon floor and then 1/4 of the way up the west canyon wall. The Shalbatana Vallis is very roughly a 300 mile (480 km) long canyon that opens up into a wider valley on the south end before reaching the Orson Welles crater. It has a delta on its northern end (Chryse Colles) and that delta connects to the larger Chryse Planitia (Golden Plain). A different mud flow at the south end of Shalbatana Vallis was recently identified by Berman D. C. et al (2017).

The upper part of this landslide is similar to slump failures on Earth that form in cohesive soils with a high clay content that progressively fails over an extended timeframe. At the top of the slide there are a few tension surface cracks (see GE image below). In an active slide, these cracks will widen and form a new scarp with a new rotating slump block. The blocks are separated by minor scarps. This slide has 3 or 4 larger slump blocks with smaller ones between. Using Google Earth, a profile section was cut through the slide to determine elevations. The section location can be seen in the GE photo above (Fig. 1).  In the landslides I have studied in Mississippi the toe is a small percentage of the whole feature. But here the base or toe of the slide is longer than the slump. Clearly, the toe is acting more like a mud or debris flow in this slide. The toe of the landslide ran about 4 miles ( km) across the floor of the canyon and then 1200 feet (665 m) vertically up the west canyon wall. This flow indicates that this whole slide happened during a single (non-progressive) event.

Google Earth image of the Shalbatana Vallis Landslide from above
 (top of photo is south)
Using Google Earth coordinates, the south end of the scarp is located at lat 4.300975̊, lon -43.988396̊and the north end at lat 4.497535̊, lon -43.991300̊. This landslide is not something that happened recently because several small meteor craters can be seen on the landslide surface. There are other smaller landslides in the Shalbatana Vallas and many hints of older landslides that appear to have lost most of their identity from erosion. But it is clear that no water has flowed down this canyon since this landslide occurred. There are numerous small craters in the floor of the canyon and a few larger craters that intersect the top edge of the canyon. These craters help date these features. When this slide occurred there was abundant water to fuel the slide, maybe one of the last places on Mars to have abundant water. It could be that a meteor impact created enough ground quake to cause the soil to liquefy thus causing the slide. On Earth similar landslides happen after there is a large influx of ground water from a heavy rain. The influx of ground water raises the pore pressures in the soil and reduces its shear strength. The factor of safety against sliding drops to unity and the side precipitates. A soil that has shear strength and then suddenly turns into a mud flow, indicates a soil that may have obtained its strength due to some cementitious agent.

The location of this landslide was submitted as an observation candidate in Oct 2008 and the Mars Reconnaissance Orbiter HiRISE camera photographed a strip of the slump area of this slide (See http://hirise.lpl.arizona.edu/PSP_010461_1845). However, the mudflow at the base of the side was not included. The nearby smaller landslide mentioned above was identified as a landslide and was nicely imaged by HiRISE 04 November 2007. See “Landslide in Shalbatana Vallas” http://hirise.lpl.arizona.edu/PSP_005965_1855 and again on 10 Jan 2009 (see http://hirise.lpl.arizona.edu/ESP_011529_1855).


References:
Berman, D. C., Weitz, C. M, Rodriguez, J. A. P., Crown, D. A, “Geologic Map of the Source Region of Shalbatana Vallis, Mars.” 3rd Planetary Data Workshop 2017.

Google earth images: NASA/USGS
ESA/DLR/Fu Berlin (G.Neukum)