Glaciers Lecture Notes PDF

Glaciers EA2110 / EA3110 LECTURE 9: 19 TH AUGUST 2024 Glacial Environments 2 Summary of Glacial Sedimentary Systems Aspect Glacial Environments Weathering Strong physical Transport Fluid flow (ice, meltwater) Deposition...

Glaciers EA2110 / EA3110 LECTURE 9: 19 TH AUGUST 2024 Glacial Environments 2 Summary of Glacial Sedimentary Systems Aspect Glacial Environments Weathering Strong physical Transport Fluid flow (ice, meltwater) Deposition Glacial terminus and outwash (melting ice) Lithification Burial, compaction Very poorly sorted, can be angular or rounded, short transport distances, ‘rock Sediment Characteristics flour’ mud component Sedimentary Rock Types Tillites / diamictites, laminated mudstones with dropstones Structureless moraine deposits (layered but not bedded), lower plane beds Sedimentary Structures and iceberg keel scour marks in glaciomarine and glaciolacustrine areas, depositional structures in pro- and periglacial fluvial systems Moraines, erratics, eskers, kettle lakes, tarn lakes, glacial striations, U-shaped Landforms valleys, horns, cirques, etc. 3  Slide Title … Perito Moreno Glacier, Patagonia 4 Why Study Glacial Environments? Google Earth Engine 5 Glacial Systems Areas of where rate of accumulation of snow or ice exceeds melting → Can extend from land to sea → Occur mostly in high latitudes, uncommon in lower latitudes (only above snowline) → Low and high altitudes → Small or large seasonal fluctuations → Deposits can be terrestrial or marine → 10% of Earth’s surface is covered by glaciers. 6 High Latitude, Low Altitude: Antarctica Google Earth Engine 7 Low Latitude, High Altitude: Indonesia Google Earth Engine 8 Low latitude, high altitude Glaciers on Mt Kilimanjaro in Tanzania 9 Ice as a Fluid Bingham Plastic: Plastic materials that have yield strength which must be overcome before deformation occurs (e.g., some debris flows w/large clasts). After yield point is exceeded, has constant viscosity). → Thixotropic substances: special plastic that behave like substances with variable viscosity after yield strength is overcome (e.g., ice). Glaciers have both high capacity and competency →Can carry significant volumes of sediment →Can carry very large material 10 11 Stable Glaciers Maintain a Balance of Ice The type of glacier will influence what sedimentological features are created Flat-ground glacier Thixotropic behaviour of ice means after reaching a critical mass, the ice begins to flow and with increasing load the viscosity decreases Credit: PeakVisor 12  Altitude: height above sea level Anatomy of a Glacier Latitude: distance from the Accumulation zone: fallen snow from equator (high latitude = closer annual precipitation compacts to form ice. to either north or south poles) As weight of snow/ice increases it begins to move downslope. Equilibrium line: under stable conditions, accumulation = ablation, head and toe of glacier remain stationery Ablation zone: in lower altitudes and higher temperatures, the glacier starts to melt Moraine: accumulation of unconsolidated glacial debris Modified from Skinner and Porter (1992) 13  Altitude: height above sea level Features of an Ice Flow Latitude: distance from the Subglacial (basal) zone: bottom of the equator (high latitude = closer glacier in contact with the bed to either north or south poles) Supraglacial zone: the upper surface Englacial zone: within the glacier Ice-contact zone: around the margins of the glacier. Proglacial environment: areas effected by melting ice, but not in direct contact (e.g. glaciofluvial, glaciolacustrine, etc.) Periglacial environment: beyond the proglacial environments. Modified from Skinner and Porter (1992) 14  Glacially Shaped Mountains Classic bowl-shaped cirque; Wrangell-St. Elias N.P., Alaska (US NPS) Classic glacial horn; Matterhorn, Switzerland (Credit: chil) 15  Ancient Glacial Landscapes: Tasmania Possible U-Shape Valley Possible Horns Cirque Ice Wedging View from Mount Rufus, leeawuleena (Lake Saint Clair), Tasmania (2023): ~270 Ma periglacial sedimentary rock shaped by 20 ka glaciers 16 Glacially Shaped Valleys Valleys carved by water are V- shaped Valleys carved by ice (glaciers) are U-shaped Abrasion is distributed across a broader area Wei ght of Ice Lauterbrunnen, Switzerland 17 Glacial valleys in satellite imagery, British Columbia / Northern Territories / Alaska 18  Glacial Erosion: Abrasion Largest volume of transported sediment resides within the basal zone of the glacier (1-15 m) Sediment concentrations average 25% but can but upwards of 90% in warmer parts Sediment may be layered but is not sorted Abundant rock flour (