Landforms Geography Glaciers

Glacial Geomorphology Development of a glacier Types of glaciers Glacial landforms History of glaciers What causes glaciation? Impact of global climate change on glaciers Periglacial processes and landscapes

Development of a Glacier Glacier – slowly moving mass of dense ice formed by gradual thickening, compaction, and refreezing of snow & water over time After summer melt, some snow left over With weight and partial melting, snow turns to Firn, crunchy transition from snow to ice Further compaction, ice crystals align, become dense glacial ice which flows slowly downslope At least 40-m thick to become glacier

Glacial Mass Budget Glacial input : Snow Glacial output : ice, meltwater or water vapor Zone of Accumulation – top of glacier where temps are cooler - input > output Zone of Ablation – lower part of glacier where temps are higher – output > input Equilibrium line – point on glacier where input = output

Glacial Formation

Glacial Mass Budget

Glacial Movement Glaciers move through internal deformation Interior of glacier like malleable plastic

Glacial Movement

Glacier Types Mountain Glaciers –Ice Cap – Continuous sheet of ice covering entire landscape –Ice Field – Buries all but tallest mountains – can be very thick –Alpine Glacier – Flows down valleys away from high country –Cirque - Bowl-shaped depression on mountain flank due to glacial erosion – snow source

Alaskan Glaciers Hubbard Glacier

Continental Glaciers Huge ice masses covering a large part of a continent or large island – also called ice sheets More than 3000 m deep in places Covers most of Antarctica and Greenland Weight of ice presses lithosphere down into asthenosphere, called isostatic depression

Continental Glaciers

Glacial Landforms Rock & debris picked up by glaciers, transported in direction of movement & deposited Glacial erosion: –Glacial Abrasion – scratch and gouge bedrock –Glacial Striations – caused by glacial abrasion –Glacial Grooves – deep striations –Glacial Plucking – boulders ripped from ground by glacier – deposited by retreating glacier, called Glacial Erratics

Glacial Erosional Landforms Roche Moutonnée – rounded hill, gradual on side toward direction from which glacier comes Glacial Striations Glacial Erratic

Alpine Erosional Landforms Glacial Erosion: –Cirque – bowl-like feature on mountain flanks –Tarn – small lake in bottom of cirque –Arête – narrow, steep ridges between cirques –Horn – mountain with 3 or more arêtes at summit –Glacial Trough – u-shape valley eroded by glacier –Hanging Valley – side trough above main trough – possible waterfall

Alpine Erosional Landforms Cirque Horn “Matterhorn” Glacial Trough

Glacial Depositional Landforms (Till) Glacial Till – sediment directly deposited by glacier – many particle sizes Moraine – winding ridge formed by till at the front or side of glacier – Moraine types: –Lateral – along former edges of glacier –Terminal – along front of former glacier –Recessional – formed as glacier recedes –Medial – between 2 glaciers –Ground – irregular deposition as glacier recedes

Glacial Depositional Landforms (Till)

Glacial Depositional Landforms (outwash) Glacial Outwash – sediments deposited by water out & under a glacier as it melts – forms Outwash Plain, flat feature in front of former glacier Kame – large mound deposited near glacier front Esker – winding ridge from water flowing in tunnel through ice under glacier Kettle Lake – big ice block fallen off glacier front is buried by outwash, melts later forming lake

Glacial Depositional Landforms

History of Glaciation As early as 2.3 B years ago, ice covered much of Earth, and off and on since then Most important Ice Age was Pleistocene Epoch, 1.8 M years ago till 10K years ago Glacial – period when glaciers expand from poles – cooler temps, lower sea level, Interglacial – period when glaciers recede: warmer temps, higher sea level

Pleistocene Glaciations Named for southern extent of ice sheet in North America –Nebraskan – 1 million yrs ago –Kansan – 625 K yrs ago –Illinoisan – 300 K yrs ago –Wisconsin – 35 K to 10 K yrs ago Laurentide Ice Sheet – eastern North America Cordilleran Ice Sheet – western North America

Maximum Extent of Pleistocene Glaciation 30% of earth’s surface covered by ice sheets (Only 11% coverage today)

Oxygen Isotopes

Evidence of More Glaciations? Ice core samples suggest more than the known 4 glaciations – show more cool, glacial periods Oxygen isotopes O-16 & O-18 both in water, but O-18 evaporates more in warmer climate, so ratio of O-16 to O-18 in ice cores can indicate relative warmth of climates over 1 million yrs ago!

Great Lakes

Causes of Glaciation Summer temp (melting) is key to glaciation Possible Factors: 1. Variations in solar radiation (dust, sunspots…) 2. Reduced carbon dioxide (escaping heat) 3. Increased volcanic activity (reflective dust) 4. Variations in Earth-Sun geometry (axial tilt, shape of orbit, rotation) 5. Plate Tectonics

Milankovitch Theory Dominant theory of causes of glaciation, based on Earth-Sun geometry: Orbital eccentricity – strongly elliptical orbit puts Earth farthest from Sun in summer, cooling it Tilt obliquity – Earth’s tilt varies from 22.1º to 24.5º - less tilt means lower angle Sun and less insolation at poles, thus cooler summers Orbital precession – wobbles of Earth’s axis - North Pole may point toward Sun at farthest point of orbit, creating a cool summer

Milankovitch Theory Orbital EccentricityAxial TiltOrbital Precession When three factors coincide, high probability of glaciation Glacial Geomorphology: Processes and Landforms

Climate Change and Glaciers Since mid-1800s glaciers have been receding, both alpine and continental Alps, Parts of Andes, Mt. Kilimanjaro melting Thousands of sq miles of Antarctica & Greenland ice sheet lost over last 30 years due to warming Melting area of Greenland has increased rapidly since early 1990s

Climate Change and Glaciers

Periglacial Processes and Landscapes In near-glacial environments – constant freeze/thaw cycle effects on landscape Permafrost – ground that is permanently frozen –Continuous – poleward of -7ºC mean annual isotherm – all surfaces frozen exp under water – avg 400 m thick, up to 1000 m thick –Discontinuous – poleward of -1ºC mean annual isotherm – thinner than continuous, esp. on south facing slopes

Extent of Permafrost

Permafrost Processes Active Layer – soil that melts & refreezes daily or seasonally – as thin as 10 cm in continuous permafrost, up to 2 m thick in discontinous Dramatic warming in arctic is making active layer much thicker & releasing tons of CO 2 Talik – body of unfrozen ground within permafrost, e.g. under a lake, important for movement of groundwater