Describe how seasonal snow melt and rains form fertile floodplains in pakistan and bangladesh

Every year Pakistan and Bangladesh are affected by the snow melting from the Himalayan mountain range, as well as seasonal monsoon rains. Bangladesh is much more affected though. These two factors create flooding of very big portion of Bangladesh, as well as the river valleys in Pakistan. With the flooding, the water brings lot of material from the mountains, most importantly biomass, rocks and sand. It makes deposits of them in the lowlands. So there's practically new fertile layer every year on the soil brought by these two factors. The soil is extremely productive and in this way it is naturally renewed every year, which makes agriculture flourish.