Chapter 7 Student Presentation Notes – 3rd Block 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 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 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 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 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 o o o o 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