17 April 2009

Large landslides in Peru and Kyrgyzstan, the Afghanistan earthquake plus heavy rain expected in the Wenchuan area

Posted by Dave Petley

Each year in mid-April we move into the global “landslide season”, when the development of the Northern Hemisphere summer, and the associated weather patterns elsewhere, means that the number of landslides starts to increase dramatically. This is all too clear from the range of landslide events in the last few days, plus the threat of heavy rainfall in the earthquake affected areas of China:

1. Major landslide in Peru
A range of news agencies (for example AFP and CRI) are reporting that there was another large landslide in Peru, again in La Libertad Province (the second major landslide this week in that province). Although details are sketchy, this time the landslide appears to have been very large (one report suggests 1 km long), hitting two villages (Chamanacucho and Aricapampa). Reports suggest that about 30 people were killed. The coordinates of Aricapampa are (-7.80583, -77.7172), which yields the following Google Earth images:

It appears that the landslide is still active, which is hampering the recovery operation substantially.

2. Major landslide in Kyrgyzstan
According to RIAN there was also a large landslide in Kyrgyzstan yesterday. The landslide appears to have hit Raikomol village Jalalabad province in in south Kyrgyzstan, killing 16 people and a large number of cattle. All of the victims, 11 of whom are apparently children, have been recovered. The ENG24 website has posted this rather grainy, but very helpful, image of the slide:

The reports suggest that it is about 300 m long. It appears to be a massive earthflow. Unfortunately the source zone is not in the image – I would be very interested to see how and where this started.

3. The Afghanistan earthquakes
The two moderately-sized (USGS Mw=5.5 and 5.1) but shallow (USGS depth = 5.7 and 3,.2 km) earthquakes in Afghanistan this morning appear to have caused damage in at least some villages, with about 20 reported fatalities at the moment. A Google Earth image of the area affected suggests that it really is a very remote zone:

Given the remoteness of the area and the rugged terrain the number of reported fatalities might well rise during the day. Earthquakes of this size would not normally cause much damage, but the early indications are that these two events really are exceptionally shallow. I would anticipate that there will have been at least some landslides in the upland areas, but probably over quite a limited area.

4. Heavy rain forecast for the earthquake affected areas of China
Xinhua is forecasting that heavy rain will hit the areas affected by the Wenchuan earthquake over the next few days. Up to 100 mm is expected to fall. This will be the first heavy rainfall of this years rainy season. Given the amount of mobile sediment on the hillsides, and the occurrence of debris flows in heavy rainfall last September, some further problems might be expected if this heavy rainfall does occur: