Glaciers and Glaciation

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Glaciers and Glaciation
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Chapter 12 objectives

• Understand glacial formations and movement
• Processes involved in glacial and interglacial
  periods
• Different types of glaciers and where found
• Processes within glaciers and movements
• Past glaciers effect (direct and indirect)

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Introduction

• Glacier large, long lasting mass of ice formed
  on land that moves under its own weight.
• Two types of glaciated terrain on Earth
• Alpine glaciation mountainous terrain
• Continental glaciation terrain is covered by
  large area of continental ice.

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Glaciers Formation and Movement

• Glacier Distribution
• Glaciers occur in temperate climate along w/
  polar climates and where more snow falls than is
  melted each year.
• Most glaciation is in polar areas 95
• 85 - Antarctica
• 10 - Arctic
• 5 - the rest
• Types of Glaciers
• Valley glaciers confined to a valley and flows
  via gravity. Alpine areas
• Ice sheet covers a large area of land
  (continental is size)
• Ice cap similar to above, yet smaller, Iceland
  and mountainous areas

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Formation of Glaciers

• Formation process snow to glacial ice AND
  sediment to sedimentary rocks.
• Snow air air squeezed out snowflakes change
  to granules granules compacted and cemented
  firn more pressure to glacial
  ice(metamorphism).
• Glacial budgets if a glacier gains outweigh
  loses, then the budget is positive and it
  expands.
• Positive budgets push and move downslope
  advancing glaciers
• Negative budgets are the opposite, they retreat
  upslope
• Balanced is neither gains or losses.
• The upper part of the glacier is called the zone
  of accumulation always covered in snow.
• The lower part of the glacier is called the zone
  of ablation, ice is lost by melting, calving, or
  evaporation.
• The equilibrium line is the highest point where
  snow is lost during a melt season. This line may
  shift each year.
• Terminus is the end of the glacier that shows a
  positive/negative budget.

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Valley Glacier Movement

• Gravity is the force behind downslope glaciers.
• Speeds are variable as a glacier moves. (a few mm
  to meters/day)
• Temperate climate glaciers move faster than
  colder regions.
• Velocity varies w/in the glacier the central
  portion of the valley glacier moves faster than
  the sides and the surface moves faster than the
  base. ?
• Basal sliding sliding of a single body of ice
  over underlying rock.
• Plastic flow the deformable lower part of the
  glacier.
• Rigid flow the upper part of the glacier that
  does not bend, it breaks forming crevasses
• CREVASSES brittle ice no deeper than 40
  meters as you fall to your death, there is a
  bottom? After the ice pass over this area, the
  crevasse closes.

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Movement of Ice Sheets

• Antarctica has an East and West sheet w/ a
  mountain in b/t.
• Western ice sheet is located on bedrock and
  covers a volcano.
• Eastern ice sheet is about 2700 meters thick, and
  at its thickest at 4776 meters. The flow is
  plastic in nature and may be covering a giant
  lake.

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Glacial Erosion

• The erosive forces of ice is huge, it scrapes,
  scours, and tears rock from floors and walls of a
  valley.
• Two ways of eroding land
• Plucking glaciers loosen and lift blocks of
  rocks and makes them part of the ice.
• Abrasion the sliding of ice is like sandpaper,
  it smoothes, polishes, and pulverizes rock down
  to rock flour.
• Erosion is controlled by four factors
• Rate of glacial movement
• Thickness of the ice
• Shape, abundance, and hardness of the rock
  fragments
• The erodibility of the rock surface

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Landforms created by Glacial Erosion

• Glaciated Valleys
• Aretes, Cirque, and Horns
• U-shaped valley and hanging valley
• Truncated spurs
• Tarns rock basin lakes

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Glacial Deposition

• Till unsorted/unlayered sediment
• Moraines till left behind a glacier
• End (terminus)the farthest progression.
• Recessional a series of temporary pauses during
  recession
• Lateral sides of a glacier
• Medial middle b/t two converging glaciers
• Ground debris left during recession
• Erratic ice transported boulder
• Drumlin till shaped like a spoon
• Outwash debris left from melt water
• Outwash plain
• Esker winding ridge of deposited material
• Kettle a small lake forms when large blocks of
  ice melt.
• Kame inverse of kettle lake (depositional hill)

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Glacial Lakes and Varves

• Lakes that form between the end moraine and the
  retreating glacier.
• Varves sediment that is deposited each year
  settles out in a pattern.
• Two layers of different colors
• Lighter color coarser sediment (silt) deposited
  during warm part of the year.
• Darker color finer sediment (clay) settles
  during the winter after the lake freezes. Dark
  color organic matter.

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Theory of Glacial Ages

• Louis Agassiz and William Buckland found evidence
  of glaciers that covered most of Europe.
• A hypothesis turned to theory when other areas
  not covered by ice experienced climates changes
  due to water redistribution.
• This is further backed up by oxygen isotope
  (O16/O18)

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Direct and Indirect Effects of the Past Glaciation

• Direct
• Scraping, scouring of bedrock. Striations
  indicate direction. Till was redistribution of
  sediment (loess). A number of depositional
  formation present. Large number of lakes formed.
• Indirect
• Pluvial Lakes formed during past time of
  abundant rainfall
• Lower sealevel due to being tied up in
  glaciers.
• Fiord coastal inlet that used to be a U-shaped
  valley.
• Crustal rebound due to the weight of the
  glacier being removed from the land and is
  still rebounding today.

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Milankovitch Cycle 1921

• Primary control for glacial and interglacial
  periods is variation in Earths orbit and
  inclination to the Sun.
• Heat is related to the angle of the Suns rays
  and distance from the Sun.
• Three factors responsible
• Eccentricity the shape of Earths orbit cycle
  of 100,000 yrs. Today we experience only 6
  difference b/t January to July. Farthest 20 to
  30. Effect the suns radiation.
• Axial Tilt 21.5 to 24.5 degrees tilt cycle of
  41,000 yrs. Today we are at 23.5 degrees. Less
  tilt more evenly distributed temperatures.
• Precession Where north is located(Vega/Polaris)
  wobble as it spins on its axis cycle of
  23,000 yrs. Greater seasonal contrasts.
• http//www.educnet.education.fr/svt/anim/ticeparis
  nov2003/hf/tp_o18/milanko.swf
• http//www.homepage.montana.edu/geol445/hyperglac
  /time1/milankov.htm
• http//apollo.lsc.vsc.edu/classes/met130/notes/cha
  pter16/graphics/71_Orbital_Fluctuations/A_71.swf

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Mass Wasting Chapter 9
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Chapter 9 Objectives

• 1. Types of mass wasting and speed of movement
• 2. Effects of mass wasting
• 3. Potential causes and what triggers the
  release of debris

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Mass Wasting

• Mass Wasting the downslope movement of rock,
  regolith, and soil under the direct influence of
  gravity.
• The Role of Mass Wasting
• Its the step that follows weathering.
• Weakens rock
• Mass wasting
• Stream transportation
• Ends up in the Sea
• Slopes change through time
• Earth is heading toward flat land. Thank
  goodness for Plate Tectonics.

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Controls and Trigger

• Gravity is the controlling force of mass wasting.
• Its a series of processes that begin to weaken
  the rock.
• The pull of gravity
• Passes the threshold of stability
• TRIGGER last of the problem
• Saturation of material w/ water
• Oversteepening slopes
• Removal of vegetation
• earthquakes

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Triggers

• Role of Water
• Cohesion holds water
• Saturation - lets it slide(when saturated)lowers
  internal resistance
• Clay becomes slick
• Oversteepened Slopes - Angle of Repose 25 to 40
  degrees
• Streams undercutting a valley
• Waves action
• Removal of Vegetation
• Root system, cuts impact of raindrops
• Removed by fire, people(timber,development)
• Fireerosion, bake the ground(slows penetration)

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More Triggers

• Earthquakes as Triggers movement
• Earthquakes and aftershock
• Liquification water saturated soils
• Landslides w/o Triggers
• Gradual weakening over time
• Other materials that fall on their own

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Classification of Mass Wasting Processes

• Type of Material
• Rock, mud, regolith, other debris can all be
  part of the mass
• Type of Motion the way the material moves
• http//www.indiana.edu/geol116/week10/wk10.htm
• Fall
• Slide
• Slump
• Flow
• Rate of Movement
• Can move at high rates of speed (160 mph) and
  everything down to 1 centimeter/year
• Some can move fast enough to produce shock and
  wind waves

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Types of Mass Wasting

• Slump
• Downward movement as a unit along curved surface
• Usually in a thick cohesive material
• Water percolates downward
• Causes can be oversteepening
• Anchor material is removed at the base
• Too much weight at the top
• Undercut by a river
• Rockslide
• Large blocks of bedrock break loose
• Usually large amounts of unconsolidated
  debris(rock slide)
• Faster and most destructed
• Can be trigged by snow and rain (spring)

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Types of Mass Wasting

• Debris Flow
• Involves soil and regolith w/ lots of water
• Mudflows characteristic of semiarid regions
• Lahars mostly volcanic material and water(like
  wet cement)
• Triggered by rapid snow melt or heavy rain
• Common on stratovolcanos
• Earthflow
• Common of hillsides in humid areas and heavy
  precip.
• Most materials are clay and silt and very
  viscous(slower)
• They can last for days to years and move as
  little as a few mm/yr

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Types of Mass Wasting

• Slow Movements cover a wider area than other
  mass wasting
• Creep gradual movement. Mainly due to freezing
  and thawing or wetting and drying gravity.
• Solification saturated soil(soggy)
• Can be promoted by layer of hardpan or permafrost
• Solification occurs in the active layer flows
  easily
• Submarine Landslides same as above ground
• Hawaii along continental slopes due to active
  volcanoes
• Many are larger than anything seen on land
• Biggest can be around Seamounts
• These landslides can have an impact on continents
  by growing the margins of the continents.