Chapter 1.3 Vocabulary Tools A B weathering the chemical or mechanical process by which a rock is gradually broken down, eventually becoming soil chemical weathering the process by which the actual chemical structure of a rock is changed, usually when water and carbon dioxide cause a breakdown of a rock agents of erosion wind, water and glaciers dust bowl when great dust storms covered the mid-western states moraines a ridgelike mass of rock, gravel, sand and clay carried and deposited by a glacier ice age the period of time when the ewarth was really cold mechanical weathering when a rock is actually broken down physically acid rain chemicals in the pollted air combine with water vapor and fall back to earth sediment small particles of soil, sand and gravel loess the windblown deposits of mineral-rich dust and silt "U" shaped valleys valleys formed by glaciers continental glaciers/ice sheets broad, flat glaciers found in Greenland and Antarctica frost wedging when water freezes into a crack in a rock; because water expands when it freezes,the ice widens the cracka nd eventually splits the rock erosion the movement of weathered materials such as gravel, soil and sand delta triangular shaped deposits of sediment at the mouth of ariver glaciers huge, slow moving sheets of ice "V" shaped valleys valleys formed by water valley/alpine glaciers found throughout the world on mountain valleys where the weather is not warm enough to melt ice