The course of the Brahmaputra River has changed dramatically over the past 250 years, with evidence of large-scale avulsion, in the period 1776–1850, of 80  km from east of the Madhupur tract to the west of it. Prior to 1843, the Brahmaputra flowed within the channel now termed the "old Brahmaputra". The banks of the river are mostly weakly cohesive sand and silts, which usually erodes through large scale slab failure, where previously deposited materials undergo scour and bank erosion during flood periods. Presently, the river's erosion rate has decreased to 30m per year as compared to 150m per year from 1973 to 1992. This erosion has, however, destroyed so much land that it has caused 0.7 million people to become homeless due to loss of land.