CEE 1030 1nd Edition Lecture 18: Glaciers and GlaciationOutline of Last Lecture I. GroundwaterII. Infiltration of waterIII. Permeability featuresIV. Groundwater movement and storageV. ReviewVI. Hydraulic gradientVII. Groundwater systemsOutline of Current Lecture I. GlaciersII. Features of glaciers and glacial movementIII. ReviewIV. Glaciers in relation to landformsa. Glacial erosionb. Glacial landformsc. Glacial depositsV. Glaciation effectsVI. Review, cont.Current LectureI. Glaciersa. Glacier: a thick mass of ice originating on land from accumulation, compaction, and recrystallization of snowb. Part of the Hydrologic Cycle and the Rock Cyclec. Covers nearly 10% of the Earth’s land surfaced. Types of glaciersi. Valley (alpine) glacier: glacier confined to a flow down a mountain valley from accumulation center at its headii. Ice sheet: very large, thick mass of glacial ice flowing out in all directionse. Formation of a glacieri. Glaciers form in areas where more snow is added (accumulation) than melts/evaporates (wastage)ii. Process1. Snowflakes become smaller, thicker, more spherical2. Air is forced out of pore spacesThese 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.3. Snowflakes are recrystallized into denser masses of small grains called firn4. Under pressure, firn fuses into a solid mass of interlocking ice crystalsII. Features of glaciers and glacial movementa. Glacial flowi. Accumulation of snow at high elevations causes glacial ice to flow downslope (affected by gravity)ii. Types of glacial flow1. Basal slip: a mechanism of glacial movement in which the ice massslides over the regolith2. Plastic flow: the movement of ice within a glacier when, under pressure, it behaves as a plastic materialb. Surface of a glacieri. Zone of fracture: the upper brittle part of a glacier where tension causes crevasses to formii. Crevasse: a deep crack in the glacier’s brittle surfacec. Rate of glacial movementi. Glaciers can move at rates of up to meters per dayii. Some exhibit intervals of extremely rapid movement called surgesiii. Calving: wastage of a glacier that occurs when large pieces of ice break offiv. Snowline: the lower limit of snow accumulationd. Glacial budget (balance)i. Advance: accumulation exceeds lossii. Retreat: loss exceeds accumulationiii. Balance: accumulation is roughly equivalent to loss (the glacial front is stationary)III. Reviewa. The Antarctic Ice Sheet contains 66% of the Earth’s freshwaterb. Glacial ice is formed from granular snow called firnIV. Glaciers in relation to landformsa. Glacial erosioni. Role of meltwater: meltwater forms and refreezes because of pressure variations at the glacier baseii. Refreezing of water traps sediment debris in the iceiii. Types of glacial erosion1. Plucking: rocks are lifted by the ice2. Abrasion: rocks within ice act as sandpaper to smooth and polish the surface belowa. Products of glacial abrasioni. Glacial polish: polished bedrock surfaceii. Glacial striations: grooves in the bedrockiii. Rock floor: finely pulverized rockb. Glacial landformsi. Glacial trough: a U-shaped valley shaped as an alpine glacier widens, deepens, and straightens a stream valleyii. Hanging valley: a tributary valley that enters a glacial trough at a considerable height about the floor of the troughiii. U-shaped valleys are usually separated by sharp ridges and peaks of bedrockiv. Lakes often form where lower areas in glacial landscapes are filled by meltwater and precipitationv. Fjord: a steep-sided inlet of sea formed when a glacial trough is partially submergedc. Glacial depositsi. Glacial drift: refers to all sediments of glacial originii. Types of glacial drift1. Till: material deposited directly by the ice2. Stratified drift: sediments laid down by meltwateriii. Tillite: rock formed when glacial till is lithifiediv. Varves: rock formed when stratified drift is lithifiedv. Erratics: ice-transported boulders, cobbles, etc. not derived from the bedrock near the present stevi. Moraines: layers or ridges of stony debris deposited along margins of or beneath a glacier1. Terminal moraine: stony debris deposited by melt at the leading edge of a glacier2. Recessional moraines3. Ground moraines: uneven veneer of till deposited beneath a glacier and exposed as the ice front retreatsvii. Drumlin: smooth, elongated, parallel hills formed of till1. Steep side faces the direction from which the ice advancedviii. Outwash plain: a relatively flat, gently sloping plain consisting of stratified drift deposited by meltwater streams leaving the glacierix. Valley train: relatively narrow body of stratified drift deposited on the valley floorx. Kettle holes: depressions created when blocks of ice become lodged in glacial deposits and meltxi. Loess: widespread, unstratified blanket deposits of windblown silt that can accumulate alongside and down-wind of glacial outwash riversxii. Ice-contact deposits1. Esker: a sinuous ridge of stratified drift deposited by a stream flowing in a tunnel beneath a glacier near its terminusV. Glaciation effectsa. Crustal subsidence and rebound results from the addition and removal of the immense weight of continental ice sheetsb. Changes in stream courses: advance and retreat of ice sheets can significantly alter the region’s drainage systemc. Sea level change: melting glaciers release water into the oceans, raising the sea levelVI. Review, cont.a. Sediment deposited by ice is generally poorly-sortedb. You would not expect V-shaped valleys on a glacial landscapec. Iowa’s rich farmland is largely a result of glacial-formed loess