Chapter 7 Student Presentation Notes
7.1
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Types of Glaciers (Crystal & Kage)
o Thick ice mass that forms over hundreds / thousands of years
o Glaciers have covered up to 30% of Earth
o An ice age is a period of time when most of Earth’s land is covered in
glaciers
o Glaciers still cover nearly 10% of Earth’s land
o Glaciers today continue to shape and sculpt these regions
o Snowline lowest elevation in a particular area that remains covered in
snow all year
 Near the top of the mountain, the closer to the equator you are
o Snow above the snowline accumulates and compacts instead of
completely melting
o The collect, transport, and deposit sediment from creeks streams and
land
o Important part of the rock cycle
o Move very slowly appears to be motionless
o A form of erosion
o Valley Glaciers
 Ice masses that slowly advance down valleys that were
originally occupied by streams
 Stream of ice that flows between steep rock walls form a place
near the top of the mountain valley
 Can be long, short, wide, or narrow
 Single or with branching tributaries
o Ice Sheets
 Enormous ice masses that flow in all directions from one or
more centers
 Cover everything but the highest land
 Continental Ice Sheets
 Much larger than Valley Glaciers
 Covers 80% of Greenland
 Accounts for 80% of the world’s ice
How Glaciers Move (Ka’Dree & Bella)
o Glacier Movement
 Ice may flow down mountain valleys fan out across plains or in
some locations spread out onto the sea
 The sheer weight of a thick layer of ice or the force of gravity
on the ice mass causes glaciers to flow very slowly
 A glacier molds itself to the land & also molds the land as it
creeps down the valley
 “Rivers of Ice” actually flow
o Types of Glaciers
2 primary types of glaciers
 Continental – ice sheets are dome shaped glaciers that
flow away from a central region and are largely
unaffected by underlying topography
 Alpine – or Valley Glaciers – glaciers in mountains that
flow down valleys
 Glaciers cause erosion by crushing and scraping along the soil
and rock they sit on
 The mass of snow and ice often pluck up rocks and boulders
and deposit then downstream
 Glacial till is assorted sediment, including soil, rock, and
boulders that are moved around by glaciers
 Grooves and striations are often made in underlying rock by
the massive moving ice
 Speeds of Glaciers
 Only about 10% of their mass is shown above surface
 Different glaciers move at different speeds
 The slower glaciers have vegetation and debris on their
surface
 Some advance several meters per day
 The area of a glacier beyond the snowline is called the
zone of wastage
Glacial Erosion (Abel & Shelby)
o Ice structures scrape and cut the rocks up from the floor and walls of
valleys
o Unlike streams they hold their sediment till they stop and melt
o They erode in two different ways
 Plucking
 Abrasion
o Plucking
 When the water from the melted glacier penetrates the cracks
of rocks, the water then freezes and expands causing rock to
break up (Mechanical Weathering)
 Glacier flows over the broken bed rock, looses then lifts the
rocks and incorporates them into the ice
o Abrasion
 Rocks embedded in the glacier act as sandpaper to smooth and
polish the surface below
 Turns pieces of rock into rock dust
 Visible by the rock dust mixing with the water melting in the
glacier that often has a grayish appearance of skim milk
Landforms Created by Glacial Erosion (Justin & Melissa)
o Before glaciation, valleys are usually V-shaped, after they are Ushaped
o Glaciers widen, deepen, & straightens valleys
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o Cirques – Bowl shaped depressions at the head of a glacial valley
o In mountain regions that have been glaciated, the valley’s are no
longer narrow
o The amount of glacial erosion depends in part of the thickness of the
ice
o Glaciers are responsible for a variety of erosional landscape features
such as, glacial troughs, hanging valleys, cirques, arêtes, & horns
o They’re surrounded by steep rock walls on three sides
o Most horns form when several cirques surround a single high
mountain
o Arêtes are snaking sharp ridges
o Horns are sharp peaks
Glacial Deposit (Bethany & Chandler)
o 2 types of glacier deposits
 Till
 Material deposited directly by glacier (unsorted
mixture)
 Stratified Drift
 Sorted mixture when deposited
o When a glacier melts all the sediments that were stored in the glacier
are deposited
 Ex) rocky pastures, wheat fields, rolling farmland
Moraines, Outwash Plains, & Kettles (Carly & Emily) (Kyler, Andrew, &
Ashley)
o Lateral Moraines
 Ridges that form along the sides of glacial valleys when glacier
melts and leaves the material it has gathered
 Medial Moraines- form when 2 valley glaciers join to form a
single ice stream
 Debris can be deposited on top of the glacier by frost
shattering of valley walls and form tributary streams flowing
into the valley
 The till (unsorted glacial sediment) is carried along the edges
of a glacier and joins to form a dark stripe debris within
enlarged glaciers
o End & Ground Moraines
 End Moraine – when ice melts, it deposits debris and forms a
ridge
 Ground Moraine – forms when glaciers begin to move away
 The glacier still delivers and deposits sediment, but
doesn’t form a ridge, they form gently rolling plains
 Clogs old stream channels and result in poorly drained
swamp lands
o Terminal & Recession Moraines
 All processes reoccur until the glacier completely melts
End (Terminal) Moraines – ridges of debris deposited at the
mouth of the glacier
 Recessional Moraines – end moraines that form when the ice
front becomes stationary during its retreat
o Outwash Plains
 Streams of fast-moving meltwater that emerges from the base
of a glacier
 A plain formed of glacial sediment deposited by meltwater
outwash at the terminus of a glacier
 Type of land formation left behind by a glacier
 Contains fine sediment that looks like milk
o Kettles
 Form when blocks of stagnant ice become buried in drift and
then eventually melts
 Thousands of kettle dot the landscape of the upper Midwest in
Wisconsin and Minnesota
o Drumlins & Eskers
 Drumlins – taller and steeper on one end Steep side face the
direction the ice came from
 Eskers – snake like ridges composed of gravel & sand.
 Sand and gravel were deposited by streams that flowed
under a glacier
 Can be several meters high and several KM ling
Glaciers of the Ice Age (Grayson & Kevin)
o Coverage during the Ice Age
 Recent Ice Age covered about 30% of the land on Earth
 It covered North America, Europe, and Siberia
o Ice Age Time Period
 The places where the most glacial coverage occurred was the
northern hemisphere and mostly in Antarctica
 The most recent Ice Age was about 2-3 million years ago
o Glacial Episodes
 Many of the major glacial episodes occurred during the
Pleistocene Epock when wooly mammoths and saber-toothed
cats roamed the land
o Ice Age Effects on Drainage
 Ice sheets greatly effected the drainage patterns over large
regions
 Before glaciation, the Missouri River flowed N toward the
Hudson Bay in Canada
 The Glacier erosion made the low lands wider
 The formation and growth of ice sheets made changed climates
beyond the glacier lines
 The change in climate changed lakes
 Ex) Nevada & Utah region
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7.2
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Geologic Processes in Arid Climates (Chad & Ashton)
o Rounded hills and curving slopes are types of humid regions
o In humid regions, well developed soils support an almost continuous
cover of vegetation
o Chemical weathering is not completely absent in deserts. Over long
time spans, clay and thin soils do form
o Iron bearing silicate minerals oxidize producing rust colored stain
o Most streams only carry water after it rains
o Permanent streams are normally found in humid regions
o Most debris in deserts are form of mechanical weathering
Basin / Range: A Desert Landscape (Jason & Kahia)
o Because desert regions lack permanent streams, they have interior
drainage
o Interior drainage is sporadic streams that don’t flow to the ocean
o Most of the streams are evaporated or taken into the ground by
infiltration
o In the United States
 An example of a dry Basin & Range is in southern Oregon, all of
Nevada, western Utah, southeastern California, southern
Arizona, and southern New Mexico
 The name Basin & Range is a perfect description for this
region, because it has more than 200 small mountain ranges
o Alluvial Fan
 A cone of debris at the mouth of a canyon
 Occasional heavy rain produces random water & moves down
the mountain canyons
 Coming from inside the canyon the runoff goes over small
slopes at the bottom of the mountain & loses velocity (speed)
 Due to a slow in velocity the load of sediment is dropped
within a short distance
o Playa Lake
 If there was a rare amount of rainfall streams may flow across
alluvial fans to the center of a basin
 This changes the basin floor into a shallow playa lake
 They only last a few days until they are either evaporated or
infiltrated
 After the water is done it is still called a Playa Lake
o The Desert Water
 Although most streams dry u, some are able to cross the arid
regions, The Colorado, or the Nile River began in well watered
mountains, with lots of water
 If there is one thing to know about the desert, it is the water
that is in it is infrequent, but important force, eroding the
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desert more than anything else, creating thinks like the Grand
Canyon
Wind Erosion (Laura & Owen)
o Deserts
 Wind erosion is a serious environmental problem
 Wind does do as much erosion as water, but is still an
important force
 Wind does its most effective erosional work in deserts because
the desert is dry and has less vegetation to hold soil in place
o Deflation
 The lifting and removing of loose particles like clay and silt
 Larger objects roll across the ground, called saltation, this
makes up bed load
 Blowouts are holes made by wind erosion in deserts
o Abrasion
 Happens when win blown sand cuts & polishes exposed rock
surfaces
 Abrasion is often credited for features such as balanced rocks
that stands high atop narrow pedestals or the detailing on tall
pinnacles, but these features are not the results of abrasion
Wind Deposits (Tyler M. & Olivia)
o Effects
 When wind is eroded it deposits sediments and creates
landforms such as Loess & Sand Dunes
 Mostly occurs in deserts & on the coast
o Loess
 Sand & Silt that are picked up by wind and deposited in other
places
 Thickest deposits of loess occur in Western & Northern China
 Loess sediment has also created the yellow river. Sediments
have gotten into the river and caused it to be yellow
o Sand Dunes
 Wind deposits sand in mounts or ridges
 The sand is deposited after the wind speed slows down and the
sand particles fall to the ground
 Once the sand starts mounting, it begins to trap more and more
sand to create a larger mount
 Once the wind becomes steady and a steady amount of sand
falls, dunes begin to form
 Dunes are steeper on the side where it gets no wind and they
are gently sloped on the side where it gets more wind
Types of Sand Dunes (Tyler P., Josie, Jacob)
o What forms Sand Dunes
 Wind direction
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 Speed
 Amount of sand available
 Amount of vegetation
Barchan Dunes
 Solitary
 Crescent shaped
 Forms on flat, hard ground where sand and vegetation is
limited
 Reaches heights of 30 m
Transverse Dunes
 Ridges are perpendicular to the direction of the wind
 Forms in series of long ridges
 Typically in coastal areas
 “sand seas”
Barchanoid Dunes
 Forms at right angles to the wind
 Intermediate between a barchans and a transverse
Longitudinal Dunes
 Long ridges of sand
 Form parallel to the prevailing wind
 Sand supplies are moderate
Parabolic Dunes
 Looks like a backwards barchans (the tips point into the wind
instead of away)
 Often forms along the coast with strong onshore winds
 Needs abundant sand and some vegetation
Star Dunes
 Isolated hills found mostly in parts of the Sierra and Arabia
Deserts
 3-4 sharp ridges in the center