LandslidesonMars

Landslides are defined as "the movement of mass, rock, or earth down a slope." (Cruden, 1991) Just as landslides occur on Earth, as a result of earthquakes, erosion, or other natural hazards, they can also occur on Mars, a planet subject to the same forces of nature. This wiki will detail the evidence for landslides on Mars and provide parallels for similar events on Earth.

Landslides are a product of many natural forces. They could be caused by earthquakes (seismic activity), excessive rain, volcanism, even by meteorite strikes to the surface of the planet in question. There is no one singular event to point to, either on Earth or Mars - on both planets, landslides have been occurring as a form of planetary landscaping since the dawn of the planet's existence. Knowledge of regional (or planetary) geology can allow scientists to determine a rough date for the landslide. This includes methods such as carbon dating or the calculation of the age of surrounding vegetation.

We are able to eliminate a few possible causes of landslides when considering them on Mars. There is no (yet known) liquid water on the planet, which eliminates the possibilities of landslides caused by excessive rainfall, ground saturation during thaw (ex: permafrost) or floods/coastal erosion, which are all contributors to landslides on Earth.

When looking for evidence of landslides, scientists search for many telltale geographical features to give them a clue as to their location:
 * scarps: roughly linear slope or cliff resulting from a fault with a vertical offset.
 * talus slopes: fan-shaped piles of rock fragments piled up against the base of a cliff, steep hill, etc.
 * rockfalls: large amounts of rock separate from a cliff or steep hill to fall, break into smaller fragments, and tumble or scrape their way down the slope.
 * debris avalanches: rockfalls in which the falling material separates into multiple fragments to flow quickly in a streamlike fashion. (Hyndman, 2009)

The USGS has published a helpful diagram of a few common types of landslides with labels of their separate parts (Figure 1, below):



**Evidence for Landslides on Mars** NASA's orbiting camera, nicknamed HiRISE (High Resolution Imaging Science Experiment), is mounted onto the Mars Reconnaissance Orbiter. It has been taking pictures of Mars since 2006. (Mars Today, 2006) While it is nearly impossible to determine the cause of a landslide solely from aerial photographs, speculation is ongoing.

Scarps are a result of faulting, and they may expose several layers of sediment. Since the Law of Superposition states that sediment deposits are evenly spaced with the youngest on the top, finding exposed layers of older sediment in a scarp with a significant amount of displaced material at its base would be a nearly unequivocal sign of displaced earth; a landslide. This is because there are very few other ways in which this situation might occur.

A countless number of scarps are documented on Mars (Bulmer, 2004) with other accostructures of landslides as well including debris flows. The HiRISE camera happened to capture a shot of at least four separate landslides in motion on Mars. With the knowledge provided by Figure 1, it is easy to identify the landslides even on another planet (see Figure 2, below):



Note the exposed layers of sediment and the debris avalanche/dust cloud that follows. Similar events happen on Earth all the time, as evidenced by this rather dramatic photographic example after an earthquake in China (Figure 3, below):



In the absence of water, another marker of landslide activity is "streak marks" in the earth. These are clearly visible in Figures 4 and 5, below. Note that these are most often found originating from an inclined point and "flowing" to a point of lower elevation. The blue color of the exposed slope in Figure 4 is not the true color, but the reflected color. There is a dust that coats everything on Mars, and the exposed slope is young enough (indicating a recent slide) that the dust has not yet coated that region. Therefore, the different age and perhaps composition of the material produces a different albedo, or reflectiveness. This illustrates changes in composition quite clearly on satellite photographs.





One may frequently find parallels to these slopes on Earth. Talus slopes, which possess fan-shaped piles of displaced material at the bottom, are another telltale sign of landslides (Figure 6). Talus deposits may come in all materials: from sand, dirt, or tiny pebbles, all the way up to giant boulders. Many talus slopes are unstable due to the loose gathering of the earth, leaving the possibility of further slide activity if weight is put on top of them.





The picture on the lower left is located near Apollinaris Patera that was photographed on Febuary 1998. The wall on this crater has about 100 dark streaks. These streaks has been formed by landslides going down the slope. The pictures above are two pictures taken at the same location but at a different time. The picture on the left was taken on February 1 1998, and the picture on the right was taken on November 18, 1998. The picture on right had darker streaks than the picture on the left because these dark streaks are younger than the pale light streaks ones on the right.

Disaster's Effects
There is no known complex life on Mars, so it cannot be said that the ongoing Martian landslides pose any serious risk to humans or other life forms. The primary interested group for these landslides is scientists themselves: geologists, astronomers, et cetera. They use what tools they can to determine the magnitude, focus and cause of the landslides.

Conclusion
In conclusion, Martian landslides pose no serious risk to human beings, but they are a valuable scientific tool. Whether comparing Martian landslide conditions to those of Earth or trying to determine if or where the planet's fault lines lie, scientists consider landslide data to be highly valuable and useful.

__Bibliography__
Bulmer, M. H.; B. A. Zimmerman, 2004. New Evidence For The Formation of Large Landslides On Mars. Lunar and Planetary Science, Vol. 35. 

Cruden, D.M., 1991. A Simple Definition of a Landslide. Bulletin of the International Association of Engineering Geology, No. 43, pp. 27-29.

Hyndman, Donald; D. Hyndman. 2009. __Natural Hazards And Disasters, Second Edition.__ Belmont, CA: Brooks/Cole, Cengage Learning.

Stiles, Lori. March 7, 2006. "HiRISE Team Releases First Processed Images From Powerful New Camera Orbiting Mars." Press Release. Accessed November 2, 2009. 

US Geological Survey. "Frequently Asked Questions." August 19, 2009. Web. Accessed November 2, 2009. 

Mars Global Surveyor. <[]>