Glacial Modification Part I Stupendous glaciers and crystal snowflakes -- every form of animate or inanimate existence leaves its impress upon the soul of man. 1 -Orison Swett Marden
Glacial Modification of Terrain The Impact of Glaciers on the Landscape Glaciations Past and Present Types of Glaciers Glacier Formation and Movement The Effects of Glaciers Continental Ice Sheets Mountain Glaciers Periglacial Environment Causes of the Pleistocene 2
The Impact of Glaciers on the Landscape Extent of Glaciations Glacial ice coverage of the land surface Today 1/10 Past 1/3 Direct Impacts Glacial topography and meltwater are the bases for many of the world s lakes and river channels. Glaciers sculpted the awesome alpine vistas. Glacial deposits are parent material for soils. Glaciers cover sizeable areas of Earth s land surface. 3
Glaciations Past and Present Pleistocene Glaciations Animation Time period Roughly the last 2 million years Climatic variability 18-19 glacial advances Intervening interglacial warming End of Pleistocene Epoch North America ca. 10,000 yrs. ago Holocene epoch began then (interglacial/post-glacial) Extent 1. End of the Last Ice Age 2. Isostasy 4
The maximum extent of Pleistocene glaciations worldwide 5
The maximum extent of Pleistocene glaciations in North America 6
The maximum extent of Pleistocene glaciations in Western Eurasia 7
Extent of Ice Coverage in the Northern Hemisphere 8
Indirect Impacts of Pleistocene Glaciers Periglacial processes and features they created Glacial outwash plains Periglacial features Sea-level changes Glaciers advanced, sea level dropped 130 m (430 ft.) lower than today Glaciers retreated, sea level rose Impacts on coastal landforms 9
Crustal depression Enormous weight of ice sheets Isostatic adjustment, crust is rebounding where glacial ice existed Response to weight loss 10
Pluvial (increased rain) developments Glaciation periods High precipitation levels in normally dry areas Copious meltwater runoff into these areas during intervening warm seasons Relatively low evaporation rates added to surplus water Large dry lake beds today» Lake Bonneville, Utah 11
Contemporary Glaciation Antarctic Ice Cap West Antarctica East Antarctica 12
Greenland Ice Cap Photo Source: NASA (Image retrieved using NASA S World Wind software) 13
North American Glaciers 14
Types of Glaciers Continental Ice Sheets Antarctica and Greenland Ice Sheets Outlet glaciers Ice shelves Iceberg formation 15
Mountain Glaciers Highland Icefields Icefield with a valley glacier and a piedmont glacier as outlets 16
Alpine Glacier Three types of alpine glaciers: cirque, valley, and piedmont 17
Tributary alpine glaciers have joined to form a very large glacier in foreground. 18
Glacier Formation and Movement Changing snow to ice Compression Coalescence 19
Zones of net accumulation and net ablation 20
Glacial Movement Animation Gravity flow Laminar flow Basal slip (Flow of Ice Within a Glacier) A flowing glacier is not necessarily an advancing glacier. 21
mass (ice) balance ice inputs (zone of accumulation) vs. ice outputs (zone of ablation) 3 conditions and landform development Inputs > outputs advancing glacier till plain end moraine inputs = outputs stationary glacier Inputs < outputs retreating glacier 22
The Effects of Glaciers Animation Erosion by Glaciers Glacial Plucking (Glacial Processes) Meltwater freezes In sub-glacial rock 23
Glacial Abrasion Grooves and striations caused by glacial abrasion near Cuzco, Peru 24
Transportation by Glaciers Drift is all material carried and deposited by a glacier. Heterogeneous collection of debris of all sizes Boulders to glacial flour Methods of Transport Bottom load transport - plucked and abraded debris Top load transport (Alpine glaciers only) - Rocks fall down high valley slopes onto ice. Bulldozing - Advancing glaciers (push) material along their front edges. 25
Subglacial meltwater transport Meltwater from top of ice flows into crevasses and tubes and ends up beneath glacier. Subglacial streams form, they carry debris beneath the ice Meltwater stream flowing over the surface of a glacier 26
Deposition by Glaciers Till debris deposited directly by ice Unstorted/unstratified drift Unsorted glacial till 27
Glacial erratic, example of till 28
Glaciofluvial deposits debris deposited by melt water Stratified drift (layered deposits) Photo Source: Pennsylvania Geological Survey (http://www.dcnr.state.pa.us/topogeo/photogallery/) 29