On April 25, 2015, Nepal was struck by a massive magnitude 7.8 earthquake. Some quick facts and figures : This event and subsequent aftershocks left over half a million households homeless, 1.4 million in need of immediate food assistance, and 5.6 million in need of immediate medical services. Nearly 9000 died and the economic cost was about $10 billion, roughly 50% of Nepal’s GDP.
Below, I survey the science behind this event, summarize the consequences, and take a more personal look at its ramifications in just one region, the Rolwaling Valley.
Accumulation and Release
Most who’ve been exposed to earth science concepts can tell you that the Himalayas are the product of a tectonic collision between the Indian Subcontinent and Asia. Far fewer, however, can describe how this process manifests. Earthquakes are the product of accumulated strain, or the deformation of rocks, which is then released suddenly. So in the case of the India-Asia collision, huge blocks of rock are deformed, storing elastic energy, which is then released suddenly through slip along a fault plane. The April 25 earthquake represented the release of a tremendous amount of energy along one of these main faults making up the structure of the Himalaya. It’s important to note that earthquakes aren’t like a bomb going off at a single point source, they occur along a plane which slips over a period of time. The point where the slip begins is called the focus…the point on the earth’s surface directly above the focus is called the epicenter.
These concepts aren’t just important to scientists. Rather, they have real, life or death consequences for humans inhabiting earthquake prone areas. Let’s explore a few of the factors that shaped this event:
- Depth. Earthquakes always happen at depth. The shallower they are, the more you feel shaking on the surface. Makes sense right? This event had a focus of just 8 km, extremely shallow for an event of its size. Many earthquakes off the coast of Japan, for example, are 80 – 100 km or even deeper. The recent Haiti quake was 10 km.
- Direction of slip. Slip starts at a point, in this case in the Gorkha region about 77 km west of Kathmandu. But the slip propagated to the east. Thus, the regions most heavily hit were just to the east such as Sindhupalchok and Dolakha where over 95% of structures were destroyed.
- Rock type. It sounds counterintuitive, but the stronger the rock you’re on, the less the shaking. Unfortunately, in a country as mountainous as Nepal, the Kathmandu valley provides one of the few flat areas to build a large city. And flat areas surrounded by mountains are usually sedimentary basins, made of soft rock. Kathmandu itself is an ancient lake, so the shaking was amplified in this region…particularly heavily hit were historic buildings such as the Durbar Squares in Kathmandu, Patan and Baktipur…UNESCO World Heritage Sites.
- Date and time. Hey, it’s not all geology. The earthquake happened at noon on a Saturday. In other words, absolutely ideal timing for minimizing human suffering. In a country with many stacked rock or brick structures that are prone to collapse, the fact that people were out and about instead of sleeping, at work or in school was a huge factor. A night or weekday could have made this event ten times more devastating.
Long road to recovery in Rolwaling
The Rolwaling Valley lies at the eastern end of Dolakha, just west of Solukhumbu, home to Mount Everest. People here are seminomadic (not sure if that’s a real term). A couple hundred inhabitants move up and down the valley with the seasons to tend to their farms and to let their livestock graze. In the photo essay below, I’ll show you a bit of my trip from Kathmandu to the end of the road and then the trek through Rolwaling. Heaviest hit was Simi Gaun, Furtemba’s home village, where he estimates over 95% of buildings collapsed. Some residents are still living in temporary housing (think: camping). People here are resilient, after all, they’ve been farming at over 15,000 feet for centuries, but they still need help. Everyone here has a story. I’ve been taken aback by how I’ve seen the houses of friends here like Angdu, Dawa Gyaljen, Mingma Gyalje destroyed. And our cook, Rajendra, showed me a huge scar on the center of his forehead, a tangible reminder of the massive icefall that killed 21 in Everest Base Camp.
The rebuilding effort is inspiring. People have come from all over the country to help build a new monastery in Beding. But it’s a tremendous effort: everything in this valley has to be carried by people for three days to reach Beding from the end of the road at a cost of 80 rupees (80 cents) per kilo. So these tremendously important community buildings like schools, health posts, and monasteries represent an enormous economic cost of about $200,000. Ultimately, this adds up to a long road to recovery for the people of Nepal.
The American Himalayan Foundation continues to take donations for earthquake relief.