The Indian plate continues to move north relative to Asia at about {{Convert|50|mm|abbr=on}} per year. This makes Nepal an earthquake prone zone, and periodic earthquakes that have devastating consequences present a significant hurdle to development. Erosion of the Himalayas is a very important source of sediment, which flows to the Indian Ocean. Saptakoshi, in particular, carries huge amount of silt out of Nepal but sees extreme drop in Gradient in Bihar, causing severe floods and course changes, and is therefore, known as the sorrow of Bihar. Severe flooding and landslides cause deaths and disease, destroy farmlands and cripple the transport infrastructure of the country, during the monsoon season each year.