GEOL 102 Mass Wasting, Glaciers, Water

Wheathering

Chemical and physical processes that produce soils, clays, sediments, and dissolved substances - a key process in the rock cycle

Erosion

Removal and transport of particles produces by weathering from their source by wind, water, and ice

Mass Wasting

Movement of Earth materials down a slope due to gravitational force. Occurs when the force of gravity exceed the strength of slope materials. Influenced by material characteristics, water content, and slope steepness

Material characteristics

Slopes may be composed of unconsolidated (regolith) or consolidated materials

Water Content

Affected by precipitation and material porosity

Slope Steepness

Influences how materials move under various conditions

Angle of Repose

Maximum angle of unconsolidated materials. It is greater for courser and less rounded materials. 35 degrees

Unconsolidated sand and silt

Form slopes with a maximum angle of repose of ~35 degrees. Steeper slopes will collapse to angle of repose

Unconsolidated mixtures

Combinations of sand, silt, clay, soil, and rock fragments (debris) can form moderate to steep slopes

Consolidated materials

Rock, lithified sediments, vegetated soils, and cohesive particles often form more stable slopes

Water Content

Affects the stability of both consolidated and unconsolidated materials. Mass movements of consolidated materials are usually linked to increasing this

Liquefaction

Occurs if water content increases enough to allow materials to flow as a fluid

Saturated materials

Will lose strength because water reduces frictional forces between particles

Stability of slopes

Depend on physical characteristics of soil, rock, and other slope materials (including water)

Shear Force

force acting on a substance in a direction perpendicular to the extension of the substance

Shear strength

the force needed to break a solid material

Natural Causes of Mass Wasting

Earthquakes, Rainfall, chemical/mineralogical changes, frost wedging/thawing

Human Causes of Mass Wasting

Adding weight, slope steepening, increasing moisture, removing vegetation

Characteristics to Classify Mass Movements

Type of material, rate of movement, mechanism of failure

Creep

Gradual downslope movement of soil or regolith

Terracettes

Structures formed by soil creep. Commonly produced by creep combined with freeze-thaw cycles, or cycles of soil saturation and drying

Solifluctions

Freeze-thaw activity generated mass movement. Thawed water saturated soil flows over frozen layer underneath. Form lobes and sheets on slopes

Slump

Rotational slope failure. Concave and cliff-like scarp (steep). Block moves coherently as one unit along the failure plane. Typically due to erosion or undercutting at base of slope

Rock Slide

Translational slope failure. Moves as one unit

Rock Fall

Fast fall of broken rocks

Mud Flow

Wet and fast movement of soil. Ie Oso Washington landslide

Hope Slide

Largest recorded slide in Canadian History. In BC east of Hope.

Frank Slide

Deadliest slide in Canadian history. Limestone slide on east face of Turtle Mountain, Alberta. Folded sedimentary rock with vertical joints and bedding planes, weathering, erosion decreased rock strength

Saint-Jude Slide

Quick clay slide initiated in Salvail River. Quebec, Montreal

Glaciomarine Clays

Deposited in sea water. The clay deposits contain up to 80% water, held together by surface tension

Vegetation Management

Maintaining, managing, planning vegetation to stabilize slope with roots

Regrading

The levelling of steep slopes into gentler ones.

Prevent Undercutting

Placing riprap (course fill to prevent erosion at base of slope)

Decrease weight on slope

Installing foam to decrease soil mass on slopes

Decreased water infiltration

Directing runoff using drainage, regulations limiting lawn watering

Bolts and Netting

Places to keep materials in place

Theory of Ice Ages

1837, Louis Agassiz. Evidence for glaciation in regions with no glaciers

Glacier

Large, long lasting river of ice that forms on land, undergoes internal deformation, and creates glacial landforms

Mauna Kea

Only Hawaiian island with evidence of glaciation. Volcanic glass formed from subglacial eruptions are used to make stone tools.

Glacial ice

Compressed, recrystallized snow, often carry large sediment loads

Location of Glaciers

High elevation, high latitudes

Glacier Landforms

Glaciers form on land, undergo internal deformation, and create __________

Brittle Deformation

Happens at glacier surface

Plastic deformation

Happens at depth

Bedrock Erosion

Ice can grind away the rock under it

Rock Flour

a fine powder of silt- and clay-sized particles that a glacier creates as its rock-laden ice scrapes over bedrock. Where glacial lake water is emptying into a lake

Glacial Striations

Once glacial is gone, there will be striations on the rock

Ice Movement

Moves by a variety of different processes including basal sliding, internal flow, and faulting. Sediment is picked up from the base of thin ice and transported up towards the surface

ice Flows

from high to low ice surfaces

Mass Balance

Relative rate of accumulation and wastage

Alpine Glaciers

Found in mountainous areas

Continental Glaciers

Cover larger areas, not confined to high elevations

Cirque Glacier

Bowl shaped glacier

Valley Glacier

A long, narrow glacier that forms when snow and ice build up in a mountain valley

Piedmont Glacier

Alpine glacier that extends down to below the mountain and spreads into a rounded bottom

Temperature Glaciers

Near their melting point, have meltwater coming off them year round

Polar Glaciers

Ice is frozen year round, ice loss primarily from sublimation (from ice to gas without melting)

Subpolar Glaciers

Seasonal melting and water runoff

Ice Shelf

a massive extension of glacial ice over water / sea

Outlet Glacier

Comes from main glaciers out to the water between mountains or rocky places

Icecaps

small ice sheets, form at high elevations

U-shaped Valley

The shape of a valley formed by the erosion of a glacier

Horn

A pyramid-like peak formed by glacial action

Arete

Ledge between the Cirques

Hanging Valley

A valley left by a melted tributary glacier that enters a larger glacial valley above its base, high up on the valley wall.

Glacial Till

Unstratified (no layers) and unsorted sediment deposited by glaciers.

Moraines

A mound, ridge, or mass of material that were left on the ground by a receding glacier.

Esker

Sorted sediments deposited by a river flowing under or through a glacier

Kettle Lakes

Depressions left by melted ice blocks

Erratics

Boulders deposited by glaciers

Outwash Plains

Found at the terminus end of glaciers. Water transports sediments deposited by the glacier. In contrast with glacial till, can find sorted sediments in these sediment deposits

Roches Moutonees

Hill features formed at the base of glaciers. Glacial plucking on the downstream side created jagged cliff. Upstream side often has striations, smoothed

Isostacy

Crust "floats" on the mantle, and the level it floats at depends on the weight of the crust. Ice sheets increase the mass over the crust where they sit, and the crust sinks

Isostatic Rebound

As mass is removed through an ice sheet melting or erosion, continents "float higher"

Glacial-Interglacial Cycles

Controlled by amount of solar radiation reaching different paths of Earth

Milankovitch Cycles

Influence how much solar radiation we get. Eccentricity, Obliquity, Precession.

Eccentricity

Shape of Earth's orbit (less or more circular) changes

Obliquity

Angle of Earth's axis changes

Precession

Wobble of Earth's axis changes, 23000 year cycle

100,000 year cycle

Eccentricity

41,000 year cycle

Obliquity

23,000 year cycle

Precession

Insolation

Energy reaching Earth's surface in the daytime

Oxygen Isotope Record

Ice to Sea level record

Warming / Cooling

Recent Temperature

Uplifting Weathering Hypothesis

Global rate of chemical weathering dependent on availability of fresh rock. Mountain chains at convergent boundaries enhance weathering. As new silicate-rich crust is exposed to weathering, atmospheric CO2 is consumed and the climate cools

Orogenesis

Mountain building, continental uplift

Cordilleran Ice Sheet

Covers West North America

Laurentide Ice Sheet

Covers East North America and Iceland

Fennoscandian Ice Sheet

Covers North Europe

High Glaciation level

Low Sea Level

High Sea Level

Low Glaciation Level

Eustacy

a change of sea level throughout the world, caused typically by movements of parts of the earth's crust or melting of glaciers.

Cooler Climate

More water stored as ice, sea level drops

Warmer climate

Water melts from ice, and sea level rises

Thermohaline Circulation

water circulation produced by differences in temperature and/or salinity (and therefore density)

Oceanic Circulation

Thermohaline circulation driven by temperature and salinity gradients. Has big influence on global climate patterns.

Oceanic Circulation 2

Transports heat around the oceans on a global scale. Patterns include vertical convection and horizontal movement

Younger Dryas

Recovery from the last glaciation was abruptly reversed and glaciers expanded significantly (12 to 13 thousand years ago)

Glacial Lake Agassiz

Melted glacial lake in Canada that drained into North Atlantic. Large pulse of fresh water distrupted the ocean currents and it cooled the climate in the Northern Hemisphere for about 1,000 years