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Wadati-Benioff zone	A sloping band of seismicity defined by intermediate- and deep-focus earthquakes that occur in the downgoing slab of a convergent plate boundary.
wadi	The name used in the Middle East and North Africa for a dry wash.
warm front	A front in which warm air rises slowly over cooler air in the atmosphere.
waste rock	Rock dislodged by mining activity yet containing no ore minerals.
water gap	An opening in a resistant ridge where a trunk river has cut through the ridge.
water table	The boundary, approximately parallel to the Earth’s surface, that separates substrate in which groundwater fills the pores from substrate in which air fills the pores.
waterfall	A place where water drops over an escarpment.
watershed	The region that collects water that feeds into a given drainage network.
wave base	The depth, approximately equal in distance to half a wavelength in a body of water, beneath which there is no wave movement.
wave erosion	The combined effects of the shattering, wedging, and abrading of a cliff face by waves and the sediment they carry.
wave front	The boundary between the region through which a wave has passed and the region through which it has not yet passed.
wave refraction (ocean)	The bending of waves as they approach a shore so that their crests make no more than a 5° angle with the shoreline.
wave-cut bench	A platform of rock, cut by wave erosion, at the low-tide line that was left behind a retreating cliff.
wave-cut notch	A notch in a coastal cliff cut out by wave erosion.
wavelength	The horizontal difference between two adjacent wave troughs or two adjacent crests.
weather	Local-scale conditions as defined by temperature, air pressure, relative humidity, and wind speed.
weather system	A specific set of weather conditions, reflecting the configuration of air movement in the atmosphere, that affects a region for a period of time.
weathered rock	Rock that has reacted with air and/or water at or near the Earth’s surface.
weathering	The processes that break up and corrode solid rock, eventually transforming it into sediment.
welded tuff	Tuff formed by the welding together of hot volcanic glass shards at the base of pyroclastic flows.
well	A hole in the ground dug or drilled in order to obtain water.
Western Interior Seaway	A north-south-trending seaway that ran down the middle of North America during the Late Cretaceous Period.
wet-bottom (temperate) glacier	A glacier with a thin layer of water at its base, over which the glacier slides.
wetted perimeter	The area in which water touches a stream channel’s walls.
wind abrasion	The grinding away at surfaces in a desert by windblown sand and dust.
wind gap	An opening through a high ridge that developed earlier in geologic history by stream erosion, but that is now dry.