Vocabulary 4 Changes on the earth's surface Tools A B weathering the breakdown of rock at or near the earth's surface into smalller and smaller pieces chemical weathering alters a rocks chemical make up by changing the minerals that form the rock dust bowl wind swept away across the Great Plain in great dust storms moraines accumalations of boulders, stones or other debris and deposited by glaciers Ice Age a cold period marked by eposides extensive glaciation alternating with episodes of relative warmth mechanical weathering breaks large masses of rock into even smaller pieces acid rain polluted air combined with water vapor and falls back to earth sediment small particles of soil, sand, and gravel loess a mineral-rich dust and silt U shaped valley glaciers carve out valleys that are rounded V shaped valleys rivers cut sharp sided frost wedging water freezes to ice in a crack in the rock erosion is the movement of weathered materials such as gravel,soil, and sand delta a triangular land form glaciers huge, slow moving sheets of ice valley/alpine glaciers found in the high valleys around the earth continental glaciers/ice sheets broad , flat (the glaciers that were in the ice age) agents of erosion agents of mechanical weathering