When the 7.8 magnitude earthquake shook Nepal, hundreds of thousands of buildings were damaged or completely destroyed, leaving millions of people homeless in an instant. However, glacial geomorphologist Dr Stephanie Mills, explains that the earthquake and its aftershocks could have far-reaching effects, causing more problems for communities already under enormous amounts of stress.
How far did the earthquake’s tremors reach?
The tremors were felt some way away from the epicentre and as far as Everest, where many glacial lakes exist.
What are glacial lakes?
Many lakes exist in Nepal at the lower margins of glaciers and these have formed as a result of glacier retreat (when glaciers melt), and increased glacial melt water.
Glaciers melt during the summer months, when temperatures are warmer, and the melt water feeds rivers. However, many glaciers create landforms at their margins called moraines, which are large ridges made up of soil and rock. Where moraines exist, they can block the flow of water and create a dam where the water builds up. These dams can breach suddenly, leading to very large volumes of water and sediment being released down valley.
What could have happened when the earthquake occurred? How would this have affected the lakes, when they are so high up? What effect would the subsequent tremors/aftershocks have had?
The tremors could destabilise the terrain in these high mountain areas, increasing the risk of landslides and may also weaken the moraines that are damming the lakes, both of which could eventually lead to glacial outburst floods.
What could happen now that the glacial lakes have been affected?
There have been no reports of glacier outburst floods so far. However, if some of the moraine dams have been weakened, this could lead to potential problems in the future.
We’re hearing reports of flooding and landslide warnings, are these likely?
The summer monsoon season is due to begin very soon and this will increase the likelihood of more landslides due to heavy rains, steep terrain and large amount of loose debris in mountain environments. If landslides occur, they can block rivers and create temporary lakes that can then burst and lead to flooding downstream. If rock avalanches fall into the dammed lakes, this can also cause the water to rise over its dam and lead to flooding.
How far down the mountain could these floods or landslides travel? What would be the effect upon these already damaged communities?
Both the landslides and floods can travel several kilometres downstream and can damage infrastructure and communities. This could have serious consequences for those communities that have already been affected by the earthquake by causing damage to life, property and infrastructure.
Dr Stephanie Mills is a lecturer in Physical Geography at Plymouth University. Her expertise lies in using glacier modelling to reconstruct past environmental change. You can find out more about the work of the university’s Geography department here.