CEE 1030 1nd Edition Lecture 18 Glaciers and Glaciation Outline of Last Lecture I Groundwater II Infiltration of water III Permeability features IV Groundwater movement and storage V Review VI Hydraulic gradient VII Groundwater systems Outline of Current Lecture I Glaciers II Features of glaciers and glacial movement III Review IV Glaciers in relation to landforms a Glacial erosion b Glacial landforms c Glacial deposits V Glaciation effects VI Review cont Current Lecture I Glaciers a Glacier a thick mass of ice originating on land from accumulation compaction and recrystallization of snow b Part of the Hydrologic Cycle and the Rock Cycle c Covers nearly 10 of the Earth s land surface d Types of glaciers i Valley alpine glacier glacier confined to a flow down a mountain valley from accumulation center at its head ii Ice sheet very large thick mass of glacial ice flowing out in all directions e Formation of a glacier i Glaciers form in areas where more snow is added accumulation than melts evaporates wastage ii Process 1 Snowflakes become smaller thicker more spherical 2 Air is forced out of pore spaces 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 II III IV 3 Snowflakes are recrystallized into denser masses of small grains called firn 4 Under pressure firn fuses into a solid mass of interlocking ice crystals Features of glaciers and glacial movement a Glacial flow i Accumulation of snow at high elevations causes glacial ice to flow downslope affected by gravity ii Types of glacial flow 1 Basal slip a mechanism of glacial movement in which the ice mass slides over the regolith 2 Plastic flow the movement of ice within a glacier when under pressure it behaves as a plastic material b Surface of a glacier i Zone of fracture the upper brittle part of a glacier where tension causes crevasses to form ii Crevasse a deep crack in the glacier s brittle surface c Rate of glacial movement i Glaciers can move at rates of up to meters per day ii Some exhibit intervals of extremely rapid movement called surges iii Calving wastage of a glacier that occurs when large pieces of ice break off iv Snowline the lower limit of snow accumulation d Glacial budget balance i Advance accumulation exceeds loss ii Retreat loss exceeds accumulation iii Balance accumulation is roughly equivalent to loss the glacial front is stationary Review a The Antarctic Ice Sheet contains 66 of the Earth s freshwater b Glacial ice is formed from granular snow called firn Glaciers in relation to landforms a Glacial erosion i Role of meltwater meltwater forms and refreezes because of pressure variations at the glacier base ii Refreezing of water traps sediment debris in the ice iii Types of glacial erosion 1 Plucking rocks are lifted by the ice 2 Abrasion rocks within ice act as sandpaper to smooth and polish the surface below a Products of glacial abrasion i Glacial polish polished bedrock surface ii Glacial striations grooves in the bedrock iii Rock floor finely pulverized rock V b Glacial landforms i Glacial trough a U shaped valley shaped as an alpine glacier widens deepens and straightens a stream valley ii Hanging valley a tributary valley that enters a glacial trough at a considerable height about the floor of the trough iii U shaped valleys are usually separated by sharp ridges and peaks of bedrock iv Lakes often form where lower areas in glacial landscapes are filled by meltwater and precipitation v Fjord a steep sided inlet of sea formed when a glacial trough is partially submerged c Glacial deposits i Glacial drift refers to all sediments of glacial origin ii Types of glacial drift 1 Till material deposited directly by the ice 2 Stratified drift sediments laid down by meltwater iii Tillite rock formed when glacial till is lithified iv Varves rock formed when stratified drift is lithified v Erratics ice transported boulders cobbles etc not derived from the bedrock near the present ste vi Moraines layers or ridges of stony debris deposited along margins of or beneath a glacier 1 Terminal moraine stony debris deposited by melt at the leading edge of a glacier 2 Recessional moraines 3 Ground moraines uneven veneer of till deposited beneath a glacier and exposed as the ice front retreats vii Drumlin smooth elongated parallel hills formed of till 1 Steep side faces the direction from which the ice advanced viii Outwash plain a relatively flat gently sloping plain consisting of stratified drift deposited by meltwater streams leaving the glacier ix Valley train relatively narrow body of stratified drift deposited on the valley floor x Kettle holes depressions created when blocks of ice become lodged in glacial deposits and melt xi Loess widespread unstratified blanket deposits of windblown silt that can accumulate alongside and down wind of glacial outwash rivers xii Ice contact deposits 1 Esker a sinuous ridge of stratified drift deposited by a stream flowing in a tunnel beneath a glacier near its terminus Glaciation effects VI a Crustal subsidence and rebound results from the addition and removal of the immense weight of continental ice sheets b Changes in stream courses advance and retreat of ice sheets can significantly alter the region s drainage system c Sea level change melting glaciers release water into the oceans raising the sea level Review cont a Sediment deposited by ice is generally poorly sorted b You would not expect V shaped valleys on a glacial landscape c Iowa s rich farmland is largely a result of glacial formed loess deposits