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Chapter 13 - Deserts and Wind Action
Midterm Number III
28
Geology
Undergraduate 1
11/09/2009

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Term
rain shadow
Definition
air loses moisture as it rises over mountains producing rain shadows on the downwind side.
Term
desert
Definition

any reagion with low rainfall

less than 25 inches

aridity index of 4 or greater

Term
internal drainage
Definition
many desert regions have internal drainage into low lying basins, forming playa lakes
Term
flash floods
Definition
this high runoff can create sudden local floods of high discharge and short duration
Term
plateaus
Definition
broad, flat topped areas elevated above the surrounding land and bounded, at least in part, by cliffs.
Term
mesa
Definition
a broad, flat topped hill bounded by cliffs and capped with a resistant rock layer
Term
butte
Definition
a narrow hill of resistant rock with a flat top and very steep sides.
Term
faults
Definition
fractures in the ground along which some movement as taken place
Term
alluvial fans
Definition
build up where stream channels abruptly widen as they flow out of narrow canyons onto the open valley floors, causing a decreasing in velocity and rapid deposition of sediment
Term
playa lake
Definition
iif no outlet drains the valley, runoff water collects on valley floor
Term
bajada
Definition
a broad, gently sloping depositional surface formed by the coalescing of individual allubial fans
Term
pediment
Definition
gently sloping surface commonly covered with a veneer of gravel, cut into the solid rock of the mountain
Term
ventifacts
Definition
rocks with flat, wind-abraded surfaces
Term
deflation
Definition
the removal of clay, silt and sand particles from the land surface by wind
Term
blowout
Definition
a depression on the land surface caused by wind erosion
Term
loess
Definition
a deposit of wind blown silt and clay composed of unweathered, angular grains of quartz, feldspar, and other minerals weakly cemented by calcite.
Term
sand dunes
Definition
mounds of loose sand grains piled up by the wind
Term
slip face
Definition
the steep downwind slope of a dune
Term
barchan
Definition
dune that develops where the sand supply is limited.
Term
transverse dune
Definition
a relatively straight, elongate dune oriented perpendicular to the wind direction
Term
parabolic dune
Definition
somewhat similar in shape to a barchan dune, except it is deeply curved and is convex in the downwind direction
Term
longitudinal dunes
Definition
large linear dunes parallel to wind direction, cross winds are likely important as well
Term
arroyos or dry washes
Definition
dry stream beds through most of the year can become full rapidly during flash flooding events
Term
sierra nevada
Definition
produces strong rain shadow effects
Term
basin and range
Definition
fault block bounded mountain ranges with valleys in between
Term
colorado plateau
Definition
region of flat lying sedimentary rocks at high elevation
Term
horsts
Definition
uplifted fault blocks that form mountain ranges
Term
grabens
Definition
downdropped fault blocks forming valleys inbetween
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