Question
Asked 1 January 2018

What are the signatures of an ancient landslide?

If we suspect a landslide to be ancient, what are the signatures we should find? So that we can prove it as ancient.

All Answers (3)

Atul Kohli
Geological Survey of India
There can be certain signatures while you are in a palaeo-slide zone. These may be geological, topographical, hydrological etc. For example, palaeo/ old scars that are developed on hill slopes/ facets, topographical breaks/ differences, especially sudden ones, palaeo/ old/ compacted debris accumulation, sudden presence/ absence of springs, emerging of new nalas/ streamlets, that may not be there on old topographical maps, level differences in a course of time, traces of ground/ tension cracks, traces of headscarp/ crown etc. etc. There may be traces of few other instability signatures as well. It depends in which kind of terrain/ slope forming material/ slope etc., in which you are expecting a palaeo-slide. Radio-carbon dating of ancient slide debris is also helpful in a certain cases.
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Vipin Kumar
Doon University
  • Topography should be relatively more concave, or convex.
  • Relatively more vegetation owing to thick debris.
  • Structural features (lineament,fault) would also be of great help.
Marco Emanuele Discenza
Geoservizi s.r.l., Campobasso, Italy
An ancient landslide is inactive and stabilized. Generally it can be classified ad relict, because it has been developed in geomorphological and climatic conditions clearly different from the current one.
Therefore, any instrumental measurements (i.e. inclinometers and interferometry) should highlight the absence of evident deformations or movements of the entire landslide body and of the main sliding surface.
However, the main elements for its identification are geomorphological. The original landslide body and its main scarp can be more or less visible, but still strongly degraded and very old. Both the crown and the main body can be affected by smaller and more recent landslides, clearly distinguishable from the original landslide. Generally the main scarp appears smoothed and strongly weathered, while the zone of accumulation is recognizable only for its convexity.
If the landslide are affected by more recent erosional or depositional processes, its identification is obviously easier. In this case, the dating of the most recent forms can provide clear indications about the age of the ancient landslide.
Finally, you need to evaluate the landslide inactivity and the climatic conditions in which it was formed. If are identifiable elements that correlate the landslide to trigger factors no longer present on the slope, it is very likely that the landslide is ancient and relict.
These are only general suggestions. Obviously, depending o the geological and geomorphological context, it is possible to identify further distinctive elements.
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