Transcript Table of Contents - Mr. Tobin`s Earth Science Class

Table of Contents
Title: Wind
Page #: 75
Date: 2/14/2013
Objective
• Students will be able to describe conditions
that contribute to the likelihood that an area
will experience wind erosion.
• Students will be able to identify wind-formed
landscape features.
• Students will be able to describe how dunes
form and migrate.
Word of the Day
• Velocity: The speed of an object and its
direction of motion.
Wind
• Wind: The horizontal movement of air across
Earth’s surface.
• Wind modifies landscapes in all areas of the
world by transporting sediment.
Wind
• Wind Erosion and Transport:
• Wind can move smaller particles.
– It can cause them to roll: “creep.”
– It can pick them up and carry them long distances:
“suspension”
– It can cause large particles to bounce up and
down: “saltation”
Wind
• Wind erosion happens in areas that are dry
and that have little vegetation.
Wind
• Deflation: The lowering of land surfaces that
results from winds’ removal of surface particles.
– Occurs when vegetation is removed and surface soil
dries out and gets blown away.
– Dust Bowl of the 1930s created “deflation blowouts”
in mid-western U.S.
– Deflation is a problem in agricultural areas and in
deserts.
– Leaves behind coarse gravel and pebbles called:
Desert Pavement.
Soil that is experiencing deflation.
Deflation blowouts in New Mexico
Oklahoma, 1930s Dust Bowl
Desert Pavement
Wind
• Abrasion: When particles of sand rub against
the surface of rocks or other materials.
– Sand contains quartz – a hard mineral that wears
away rock.
– Characteristics of wind abrasion:
• Rocks are pitted and grooved.
• Rocks become polished on windward side and develop
smooth surfaces with sharp edges.
Wind
• Ventifacts: Rocks shaped by windblown
sediments.
– “Arches”
– “Pillars”
Wind
• Wind Deposition:
• When wind velocity slows
down, particles are
deposited.
• Dunes: A pile of wind
blown sand.
– Dunes develop where an
object – rock, landform,
vegetation – blocks
forward movement of
particles.
– Sand continues to be
deposited as long as winds
blow in one direction.
Wind
• Dune Profile: The side from which the wind is
blowing will have a gentler slope: “Windward
side.”
– The steeper side is called the “Leeward side” and is
protected from the wind.
Windward
Leeward
Wind
• Different Types of Dunes: Determined by wind
direction, vegetation, wind velocity and the
amount of sand.
• Dune Migration: Dunes move as long as wind
blows sand hard enough to cause it to blow of
the windward side and onto the leeward side.
Different Types of Sand Dunes
Wind
• Loess: Thick windward silt deposits.
– Loess soils are very fertile because they contain
abundant minerals and nutrients.