Chapter 7 Student Presentation Notes – 3rd Block
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Types of Glaciers (Diana & Haley M)
o Up to 30% of the Earth is covered in glaciers
o Ice age – a period of time when much of Earth’s land is covered in glaciers
o Glacier – thick ice mass that forms over hundreds / thousands of years
o Today glaciers still cover up to 10% of the Earth
o Glaciers originate on land where more snow falls each winter than melts each
summer
o Snowline – is the lowest elevation in a particular area that remains covered in
snow all year
o Further pressure from added snow above changes the coarse grains into
interlocking crystals of glacial ice
o Glaciers look like they are motion – less but they do move
o Glaciers are dynamic agents of erosion
o They accumulate, transport, & deposit sediment
o Glaciers are an important part of the rock cycle
o Valley Glaciers
 Ice masses that slowly advance down valleys that were originally
occupied by streams
 A stream of ice that flows between steep rock walls from a place near the
top of the mountain valley
 Can be long or short
 Advance only cm to m a day
o Ice Sheets
 Enormous ice masses that flow in all directions from one or more centers
and cover everything but the highest land
 “Continental Ice Sheets” because they cover large regions where the
climate is very cold
 Huge compared to Valley Glaciers
 Covered much of North America in the recent ice age
o Antarctic Ice Sheet accounts for 80% of the world’s ice, and it holds 2/3 of the
Earth’s freshwater
How Glaciers Move (Baylen & Claudio)
o Plastic Flow
 Starts about 50 m below the surface
 Ice moves within the glacier because of excess weight on the top
 Causes it to distort shape and there for crack and move
o Basal Slip
 Bottom of the glacier starts to slip or move
 Top of the glacier slides behind and just hitches a ride
 Front of the glacier destroys everything in its path leaving these great
crevasses
o Other ways glaciers move
 Heat melts and weakens or cracks the ice
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Heaviness of the ice makes it too much and it falls off inot the
ocean or on land
 These cause massive waves that some people like to surf on
Glacial Erosion (Brandon & Luke)
o 2 main ways
 Plucking
 Abrasion
o Plucking
 Melted part of the glacier fill the cracks in rocks and break them up as it
refreezes and thaws (Mechanical Weathering)
 As the glacier flows over the fractured bedrock surface, it loosens and lifts
blocks into the ice
o Abrasion
 As the glacial ice and its load of rock fragments slide over bedrock
 They work together to smooth the surface below (kind of like sandpaper)
 Rock produced by this process is called rock flour
o Factors controlling Erosion
 Rate of glacial movement
 Thickness of ice
 Shape, abundance, and hardness of the rock fragments in the ice at the
base of the glacier
 The type of surface below the glacier
Landforms Created by Glacial Erosion
o Thick mass of ice call a glacier moves down in a V shape valley where once a
stream remained and then deepens and flattens the valley
o Glaciated Valleys
 As the glacier slides down a valley once occupied by a stream the glacier
widens, deepens, and straightens the valley
 V shaped valley turns into a U shape valley
o Cirques
 A bowl shaped crater at the beginning of a glacier valley that is
surrounded by steep rock walls on 3 sides
 Begin when irregularities form in the mountain side
 Rock plucked from along the sides of the bottom
 Then a glacier will act as a conveyer belt and will carry debris away and
then can create a small lake in the basin of Cirques
o Arêtes and Horns
 Valley glacier can create other mountain landscapes such as Aretes and
Horns by curvy sharp corners
 Sharp pyramid peaks also
 Covering Cirques happen on opposite sides of divide
 When these cirques grow they split creating a very pointy ridge, and are
narrow
Glacial Deposit (Ean & Ashley)
o Transport and carries a lot of rock that is taken from the underlying bedrock
o Only a small amount is carried on the surface from mass wasting
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o 2 types of glacial deposits
 Till
 When material is deposited directly by the glacier
 Deposited as a glacier melts and drops its large amount of rock
debris
 Stratified
 When sediment is layered down by glacial meltwater in layers
 Contains particles that are sorted according to size and weight of
debris
 Consists of sand and gravel
Moraines, Outwash Plains, & Kettles (Isaac, Martha, & Trent) (Fernando, Jada, &
Daniel)
o Lateral Moraines
 Debris deposited along the sides of a glacier
o Medial Moraines
 Form from 2 merging valley glaciers
o End Moraines
 When the rock debris is carried to the back and the ice melts it deposits
the debris and forms a ridge
 The longer the glacier stays still the longer the end moraine grows
o Ground Moraines
 When the glaciers deposit sediment as the ice melts and forms a gently
rolling plain
o Terminal & Recessional Moraines
 Farthest end moraine is the terminal moraine
 During the stationary the ice front forms a end moraine that are called
Recessional end moraine
o Outwash Plains
 Water melts off of glaciers and carries sediments down with it and
deposits it in a ramp like structure
 Outwash plains hold kettle lakes in them
 Also known as sandurs
o Kettles
 Depression or small lakes
 Form when blocks of ice become buried in drifts and eventually melt
 Leaves pits called glacial sediments
o Drumlins
 Are hills composed of till
 Taller and steeper on one end of the hill
 Steep side of hill is the direction from where the glacier came from
 Often in clusters
o Eskers
 Snake like ridges
 Composed of sand and gravel
 Deposited by streams once flowing in tunnels beneath glaciers
 Mined for the rich sand and gravel they contain
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Glaciers of the Ice Age (Lauren & Landon)
o What is a glacier?
 A slowly moving mass or river of ice formed by the accumulation and
compaction of snow on mountains or near the poles
o What is an Ice Age?
 A glacier episode during a past geological period
o Vocabulary you need to know
 Erratics: path of the glacier
 Ice: frozen water
 Snow: cold precipitation, can cause loss of fingers and/or toes
o How do these things tie into together?
 During the recent ice age 30% of earth’s land and sea were covered by
glaciers and the rest covered in sheets of ice or snow
o North vs. South
 Northern hemisphere had 2x the amount of snow and ice than the
Southern hemisphere
o The Affect on Drainage
 Greatly affected by glaciers
 As glaciers creep along they pull and transport sediments to
create erractics, which can change paths of rivers
Geologic Processes in Arid Climates (Will & Haley)
o Humid regions and deserts
 Rounded hills and curving slopes are typical in humid climates
 Deserts have angled rocks, sheer canyon walls, and pebble covered
surfaces and sand
 Despite this, the same geologic processes occur in both the desert and
humid climates
o Weathering
 Most weathering in these climates are mechanical
 Chemical weathering does occur, but is rare
o The Role of Water
 Permanent streams are common in humid climates
 In deserts you can usually find bridges with no water under them
 Most streams in the desert are ephemeral, these are known for dangerous
flash floods after heavy rain
o Other facts
 Ephemeral streams = only carry water when it rains
 Flow only for a few days or weeks per year
 Humid regions have rounded rocks
 Deserts have more pointed rock
Basin / Range: A Desert Landscape (Sam & Stone)
o Arid regions typically lack permanent streams
o Interior drainage, which means streams don’t flow to the ocean
o Basin and Range region includes the majority of the west
o Called Basin and Range regions because of mountains rising above basins
separating them
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o Alluvial Fan – the results of a cone of debris from runoff
o Basin and Ranges form when the mountains surrounding on area are larger then
the center creating a basin
Wind Erosion (Christine, Abby, Squid)
o Wind erosion is the blowing away of soil, sand, or any substance light enough for
the wind to carry
o Wind DOES NOT do as much erosion on land as water does
o Wind does the most erosion in places like the desert because it is very dry and
does not have any plants to hold the soil in place
o Strong winds pick up, transport, and deposit big loads of sediment
o Wind erodes in 2 ways
 Deflation – the lifting and removal of loose sediments like clay and silt
 Abrasion – wind blown sand cuts and polishes exposed rock surfaces
o Effects / Problems
 Reduces the capacity of the soil to store nutrient and water
 Airborne and detached soil particles break soil mixtures and lower
infiltration rate
Wind Deposits (Jamie & Rhett)
o The wind creates landforms when sediment are deposited, mainly in deserts and
coasts
o Both Loess & Sand Dunes are land features created by the wind
o Loess
 Wind blown silt that blankets the landscape
 Yellow River
 Dust storms over thousands of years picked up material, then transported
it and later deposited it
o Sand Dunes
 When winds commonly deposit sand in mounds or ridges called dunes
 Dunes often are steeper on the side the wind is not facing, and are more
gently sloped on the side facing the wind
 Cross Beds – formed as sand is deposited on the sheltered side
o How do Sand Dunes work?
 Once sand blows over the dune, the wind slows and drops out
 Sand dunes come about by sand mounding up and keeps trapping more
and more sand and eventually becomes a dune
 Unlike Loess, which forms a blanket layer over big areas, winds just
deposit sand in mounds, later known as dunes
Types of Sand Dunes (Sean, Braden, Aylin)
o Sand dunes are deposits of sand that form in mounds or ridges
o Form depending on wind direction and speed, how much sand is available, and
the amount of vegetation
o 6 types of dunes
o Barchan Dunes
 Crescent shaped
 Form on flat, hard ground where sand and vegetation are limited
o Transverse Dunes
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 Form with steady winds, lots of sand, and sparse vegetation
 Ridges are perpendicular to the wind direction
Barchanoid Dunes
 Common dune
 Intermediate between a barchans dune and a transverse dune
 Rows of sand form at right angles to the wind
Longitudinal Dunes
 Long ridges of sand that form parallel to the wind
 Occur where sand supplies are moderate nd the wind direction varies
slightly
Parabolic Dunes
 Look like backwards Barchans Dunes
 Form where some vegetation covers the sand
 Often form along the coast where strong onshore winds and lots of sand
are available
Star Dunes
 Isolated hills of sand
 Their base resembles stars and usually have 3-4 sharp ridges that meet in
the middle
 Found in Sahara & Arabian Deserts