Why does volcanic activity often lead to high rates of erosion and sedimentation?
Explosive eruptions that destroy vegetation and deposit volcanic rocks and ash over wide areas create conditions that (1) promote increased rates of surface runoff during rainstorms; and (2) dramatically increase the availability of loose debris that can be eroded and transported into river valleys. The destruction of vegetation combined with deposition of tephra on hill slopes reduces the amount of water that normally soaks into the ground or is transpired by plants. The increased overland flow of water erodes rock debris from hill slopes and carries it into river valleys. There, sediment can accumulate and can alter the hydraulic characteristics of the river channel.
