GEOL 102 1st EditionExam # 2 Study Guide Lectures: 6 - 11Lecture 6 (January 29th)Climate Change and GlaciersClimate Change: Average temperature will rise 3.2*F to 7.8*F by 2100, sea level rise by 7 inches to 23 inchesUSA is the leading emitter (25%), China and India are on the riseSince the last IPCC report (2001), we’ve experienced 7 of the 10 warmest years on recordThe current warming trend is unique in the last 1300 yearsWarming will continue even if CO2 emissions stop todayHistorical Context of Glaciers: Observations of drift (Europe 1820s): found far from sources, large boulders hindered cultivation, found in wide valleys, unsorted deposits (unlike river sediments), erraticInterpretations of glacial drift: Great Deluge (flood), Glacial origin: Louis Agassiz notes that glaciers can carry large boulders, do not sort sediment, melt and leave depositsDeems “a great ice age” during glacial origin, evidence was widely found and gained acceptance in the 1860sGlacial Extent: Currently 10% of landmass is covered by glaciers, 12.5 million km squared in the South Polar region and 2.1 million km squared in the North Polar regionHow do you make a glacier? Ice crystals: minerals are solid, inorganic, have a defined structure and compositionTransformation to glacial ice:1. Accumulation and compaction2. Initial snow is 90% air3. Ends are blunted by melting or sublimation – 90% air4. With overburden there is pressure melting5. Firm snow, packed – 25% air6. Water recrystallizes in voids – 20% airLecture 7 (February 3rd)Making Glaciers and Glacial MovementTypes of glaciers: Alpine- mountainous areas, topographic control on ice movement, Continental(ice sheets)- spreads over large areas (thousands of square kilometers), unconfined by topography, today found in Antarctica and GreenlandMaking GlaciersKey requirements: cold (snow won’t melt in the summer), snowfall accumulation, gentle slope surface (accumulation without avalanches)Controls on glacial occurrence: Altitude (temperature decreases with elevation) and latitude (the distance from the equator), glaciers are much closer to sea level near the polesGlacial Movement: glacial ice has a much higher viscosity (resistance to flow) than waterStyles of movementBasal sliding: meltwater accumulates at base of glacier, fluid pressure reduces friction, common in temperate glaciers (warmer areas), regelation is a mechanism of basal sliding(on up-glacier side of obstructions, pressure melting occurs; on down-glacier side, water re-freezesInternal movement: plastic-like flow, ice crystals deform, shearing (ice crystals slide past one another), polar glaciers (base is frozen to the ground)Fracturing: brittle behavior (cracks or fractures), ice near the surface (upper 60m), crevasses, hazardousPlastic flow: below 60m depthInfluences on glacial velocity: frozen to bed, fluid pressure (meltwater at base), obstructions on the bed, sediment-laden base of glacierRates of movement: highly variable (anywhere from near 0 to 300m a year), water is a big factor (temperate glaciers are faster than polar glaciers), spatially variable (friction along the walls, affects the velocity gradient)Glacial surges: buildup of water pressure, short-term acceleration, water drainage slow it down, velocities are anywhere from 20-100m/dayMovement is driven by gravity: sloping surface (valley glacier), gravitational spreading (ice sheets, think of the honey example; due to gentle surface, pressure building with thickness, there is a lateral movement to release pressure)Lecture 8 (February 5th)Glacial Budget, Glacial Erosion and Landforms, Ice AgesWith no slope, you need lots of icy accumulation, so a glacier can’t have no slope and be thinStress at base of glaciers tends to increase when slopes are steep and ice is thickGlacial Dynamics: movement is driven by gravity, sloping surfaces are valley glaciers, gravitational spreading happens on a flat surface and pressure builds with thicknessThe Glacial BudgetZone of ablation: loss of ice near the base of the glacier; an area with sublimation, melting (meltwater pools accumulate and travel under the glacier to form small streams underneath), calving (avalanches)Zone of accumulation: where a glacier is gaining mass, the upper portion of a glacier, winter snow does not meltAn equilibrium line separates the two zonesBalancing the budget: negative budget is when ablation exceeds accumulation and the glacier retreats, positive budget is when accumulation exceeds ablation and the glacier advances, steady budget is when ablation and accumulation are equal and there is no size changeGlacial Erosion and LandformsDepositional landforms: glaciers are like conveyer belts with depositing sedimentMoraines are glacial deposits (till)Lateral: what the glacier picks up on its valley walls, medial: when two glaciers meet and their lateral moraines combine, end: when the glacier terminates, recessional: deposits made by the receding glacierMechanisms: Glacial abrasion (sediment at base, striations polish, reveals the flow direction), glacial quarrying (plucking blocks of rocks, leaves chattermarks)Erosional Landforms: cirques (bowl-shaped depressions), arête (ridge between cirques), horn (series of meeting arêtes), u-shaped valleys, hanging valleysIce Ages: prolonged periods of cold temperatures, hundreds of millions of years apart, extensiveglaciation, evidence in the form of tillites (glacial deposits)Current Ice Age (Pleistocene): since 65 million years ago there has been a gradual cooling of ~10*C, it began 2-3 mya (evidence in the form of widespread glacial deposits, sea ice near the poles, ice sheets growing from the poles, mountain glaciationIce Ages have occurred 4-5 times in Earth’s history, they persists for millions of years, there is no cyclicityWhat do ice ages have in common?Sizable amount of land mass at or near poles, land surfaces with high elevation, nearby oceans to provide moisture, ocean circulation, driven by plate tectonics, additional factors (CO2, bioactivity, volcanic activity, weathering of rocks)Fluctuations within ice ages: cycles of glacial advance and retreat, terrestrial records (4-5 episodes in the last 0.5 million years- limited by preservation deposits), marine records (25-30 cycles over 3 million years, determined using isotopes in planktonic shells deposits on seafloor)Strong periodicity: glaciations (60k-100k years), interglacials (10k years), too rapid for plates,insolation, varies with