One example is of Hattian Landslide, Kashmir, Pakistan that was triggered by earthquake, 2005. This landslide is situated very near to trace length of Bagh-Balakot Fault and at the landslide locality, this fault was also known as Tanda Valley Fault in the previous literature. Second example is Attabad Landslide (although aseismic landslide), Hunza valley, Pakistan. During a geomorphological mapping campaign carried our during a project, a fault was also inferred.
Dear Ijaz, I am not a geologist but as a geomorphologist I can say that a fault line can be a major driving factor but not every gigantic landslide can be attribuited to faultlines.
Faults often are associated with geological discontinuities and dip slopes, both can result in surface landslides due to different lithologies and sedimentary paleo-environments. Think about a layer of evaporites in an alpine setting which is overlayed by a karstic layer coming from a nearby units. The fault is responsible of getting two units together that, given an important slope, can result in hydrogeological instabilities. This is due to surface water percolation thru the limestone and its karsification and erosion of the underlying evaporites layer.
This example shows you how a fault can set things together and generate areas of instabilities, but it is generally gravity and sub-surface erosion to cause gigantic sheet-on-sheet landslides, (excluding earthquakes in active faults and barrier-generated issues, obviously), this can occur far away from the actual faultline, as well as directly underneath it.
I hope this helped a bit,
Nic
I just want to say that I think that Nicolas has answered your question very well - the presence of a fault is a sufficient condition but not a necessary condition.
I absolutely agree with what Nicolas and Dwight said.
Ljaz, the answer to your question is definitely: no!
Ijaz, most of the bigger landslides are triggered because of the instability caused due to many factors and a fault is one of them, and not the only one.
Miroslav....I have studied the gigantic Eocene Heart Mountain Slide in Wyoming, USA for most of my career. There were many causes to the regional instability there that made conditions favorable for the Slide to occur. These included the rapidly accumulating pile of Eocene volcanic rocks, active erosion along the toe of the slope in the adjacent Big Horn Basin, and earthquakes associated with the waning stages of the Laramide Orogeny. All landslides need a trigger, and earthquakes commonly serve in this role. In the case of Heart Mountain, we believe now that a kimberlite eruption may have been the triggering event. If you like, I can send you a copy of our manuscript in the review process at the Journal of Geology that explains this.
Dear David,
I will be very glad if you can send me the manuscript. It will be very usefull for me and I will enjoy reading it. You can send it to my e-mail: [email protected]
Thank you very much.
Best regards: Miroslav
No necesariamente porque hay otros factores más importantes. Fallas activas son poco frecuentes.
Raul Campillo
Kashmir, Pakistan is very active tectonic zone of collision so is not hard to find a fault line in the vicinity of every gigantic landslide, but if this fault line has a morphogenic relation with the genesis of the landslide is strictly individual for each case and can not be generalized as Nicolas staeted above.
Bellow I attached a picture of Landslide in SW Bulgaria where the fault surface of a existing listric fault is playing rolle first as a sliding surface and second as water impermeable layer.
Dear Ijaj,
In addition to previous answers, i think gigantic landslides require a regional aspect of tectonic setting in which faults are surface manifestations. In stead of faults which result into rockmass shearing by altering lithology and hence affecting slope stability, try to understand the landslides in context of climate variability alongwith active tectonic.
Hello Ijaj
As suggested by other commentators, spatial distribution of landslides in mountains might be controlled by major structures as these are often the zones of weak strata and lithological variability. But a fault might or might not be active in the particular time frame to cause slope failures. And besides structurally controlled landslides are often isolated cases affecting a localised area.
Nevertheless, often a trigger is required to generate the mass movements (mobilisation of sediments/strata) which can be along a structure, or sediment rich zones like paraglacial zones, old debris or alluvial fans. Without a trigger sediments may be stored in a particular segment without causing any major damage. And such trigger can be in form of earthquakes (like Hattian) or heavy precipitation in otherwise arid areas (like Attabad). If you are trying to see the cause of slope failures in a larger area you would need to look into geomorphological aspects, structure and climate in totality. One process might trigger landslides in one region while other region region may be completely insensitive to the same trigger.
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