watershed
See drainage basin.
water table
The surface that lies between the zone of aeration and the underlying zone of saturation.
wave-cut bench
A relatively level surface formed when waves erode the base of a cliff, causing the overlying rock to fall into the surf. A wave-cut bench stands above the water and extends seaward from what remains of the cliff.
wave refraction
The process by which a wave approaching the shore changes direction due to slowing of those parts of the wave that enter shallow water first, causing a sharp decrease in the angle at which the wave approaches until the wave is almost parallel to the coast.
weathering
The process by which exposure to atmospheric agents, such as air or moisture, causes rocks and minerals to break down. This process takes place at or near the Earth's surface. Weathering entails little or no movement of the material that it loosens from the rocks and minerals. See also erosion.
welded tuff
A volcanic igneous rock that forms when still-warm tephra accumulates at the Earth's surface. Because the particles are still warm and soft, they can weld together under the weight of overlying deposits, forming a hard rock.
wetland
A lake, marsh, or swamp that supports wildlife and replenishes the groundwater system.
wind abrasion
The process by which wind erodes bedrock through contact between the bedrock and rock particles carried by the wind.
xenolith
A preexisting rock embedded in a newer igneous rock. Xenoliths are formed when a rising magma incorporates the preexisting rock. If the preexisting rock does not melt, it will not be assimilated into the magma and will therefore remain distinct from the new igneous rock that surrounds it.
X-ray diffraction
The scattering of X rays passed through a mineral sample so as to form a pattern peculiar to the given mineral.
yield point
The maximum stress that a given rock can withstand without becoming permanently deformed
zone of ablation
The part of a glacier in which there is greater overall loss than gain in volume. A zone of ablation can be identified in the summer by an expanse of bare ice. See also zone of accumulation.
zone of accumulation
The part of a glacier in which there is greater overall gain than loss in volume. A zone of accumulation can be identified by a blanket of snow that survives summer melting. See also zone of ablation.
zone of aeration
A region below the Earth's surface that is marked by the presence of both water and air in the pores of rocks and soil. Also called aeration zone.
zone of saturation
A region that lies below the zone of aeration and is marked by the presence of water and the absence of air in the pores of rocks and soil.
