GEOL 102 1st Edition Lecture 7Outline of Last Lecture I. Climate ChangeII. Historical ContextIII. Glacial ExtentIV. How do you make a glacier?Outline of Current Lecture I. Types of GlaciersII. Making GlaciersIII. Glacial MovementCurrent LectureI. Types of GlaciersAlpine: mountainous areas, topographic control on ice movementContinental (ice sheets): spreads over large areas (1000s km squared), unconfined by topography, today found in Greenland and Antarctica II. Making GlaciersKey RequirementsCold: snow doesn’t melt in the summerSnowfall accumulationGentle surface slope: accumulation without avalanchesControls on Glacial OccurrenceWhat controls temperature?These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Altitude: temperature decreases with elevationLatitude: distance from the equatorGlaciers are much closer to sea level near the polesIII. Glacial MovementGlacial ice has a much higher viscosity (resistance to flow) that waterStyles of MovementBasal SlidingMeltwater accumulates at base of glacierFluid pressure reduces frictionCommon in temperate glaciers (warm areas)Mechanisms of basal sliding:Regelation: on up-glacier side of obstructions, pressure melting occurs; on down-glacier side, water re-freezesInternal MovementPlastic-like flowIce crystals deformShearing: ice crystals slide past one anotherPolar glaciers: base frozen to groundFracturingBrittle behavior (cracks or fractures)Ice near the surface (upper 60m)CrevassesHazardousPlastic FlowBelow 60m depthInfluences on glacier velocityFrozen to bedFluid pressure (meltwater at base)Obstructions on the bedSediment-laden base of glacierRates of movementHighly variable: ~0-300 m/yrWater is a big factor: temperate glaciers are faster than polar glaciersSpatially variable: friction along walls, velocity gradientSurges: buildup of water pressure, short-term acceleration, water drainage slows it down, velocities are anywhere from 20-100 m/dayMovement driven by gravitySloping surface (valley glacier)Gravitational spreading (ice sheets) (honey example)Gentle surfacePressure builds with thicknessLateral movement release