3 October 2010

Continued debris flow activity in the Wenchuan (Sichuan) earthquake area

Posted by Dave Petley

A frequently-forgotten but potentially very damaging impact of large earthquakes in mountain areas is the increased occurrence of debris flows and other landslides in the following years.  Whilst these events continue to represent a hazard in their own right, they frequently also cause changes to river dynamics, with resultant high levels of damage.  This problem was illustrated all too clearly in a small village that we visited close to Beichuan last week.  For those who would like to locate the village. my iPhone GPS said that we were at 32.13N, 105.54E.  This small, remote village of about 200 people lost about 20 residents in the earthquake itself.  However, the real impact has come in the aftermath.  This small factory was main source of employment in the area.  It survived the earthquake but has been destroyed by repeated debris flows that have occurred every summer since the earthquake:

If you look carefully you can see the brown mud stains and splatters up the wall that show the height of the flood at its height.  The river bed is continuing to aggrade (increase in elevation due to sediment accumulation) at this point, slowly burying the ruins.

Upstream the village itself shows clear signs of the damage to houses and other structures from the earthquake shaking:

In some cases repairs to the buildings had started before the debris flow activity started:

However, the ongoing landslide activity, and resultant changes to the riverbed, are proving to be devastating, with high levels of hazard and repeated burial of buildings:

The effect is to hugely reduce the rate at which reconstruction can occur, and to greatly increase poverty as the the people have lost both their assets and their most productive farmland.  As a result, two years on they are still living in the emergency huts constructed after the earthquake, which are now becoming fossilised into permanent structures, albeit of a poor quality:

Unfortunately, these problems are likely to persevere long into the future, leaving the population with serious challenges for decades to come.  Unfortunately, a key impact is likely to be to drive the young into urban areas, leaving rural areas populated by elderly people living in a state of great poverty.