Glaciers, Wind, and Desert Environments PDF

METU-GEOE 231 GLACIERS, WIND AND DESERT ENVIRONMENTS 1/119  METU-GEOE 231 Glaciers: A Part of Two Basic Cycles in the Earth System  Glaciers are a part of both the hydrologic cycle and rock cycle  Glacier...

METU-GEOE 231 GLACIERS, WIND AND DESERT ENVIRONMENTS 1/119  METU-GEOE 231 Glaciers: A Part of Two Basic Cycles in the Earth System  Glaciers are a part of both the hydrologic cycle and rock cycle  Glacier  a thick mass of ice that forms over land from the compaction and recrystallization of snow and  shows evidence of past or present flow  Types of glaciers  Valley, or Alpine glaciers – form in mountainous areas  Ice sheets, or continental glaciers  Large scale  e.g., Over Greenland and Antarctica  Other types  Ice caps and piedmont glaciers 2/119  METU-GEOE 231 Glaciers: A Part of Two Basic Cycles in the Earth System  Glaciers are flowing streams of ice  Glaciers have a zone of accumulation where snowfall exceeds losses  Accumulation can be due to  high altitude (mountain glaciers) or  cold climate (continental glaciers)  Glaciers have a zone of ablation where losses exceed snowfall  Glaciers are governed by a balance of snowfall, ice flow, and ablation  Glaciers retreat by melting back, not by retracting  Glaciers produce distinctive landforms and small scale features 3/119  METU-GEOE 231 Snowfall vs Melting & Evaporation (Ablation)  Zone of Accumulation  Mountain  Continental (Greenland, Antarctica)  Zone of Melting or Ablation  Terminus of Glacier  Ablation = Accumulation+ Flow 4/119  METU-GEOE 231 Glacier Types 1. Valley (Alpine)  Found in mountainous areas  Smaller than ice sheets  Lengths greater than widths  Only cover a small region  Transform V-shaped valleys into U -shaped valleys  Makes the land more rugged 5/119 Valley (Alpine) Glacier METU-GEOE 231 6/119 U-Shape Made by a Valley Glacier METU-GEOE 231 7/119  METU-GEOE 231 Glacier Types 2. Ice Sheets (Continental Glacier)  Large scale – cover 10% of Earth’s land  Found in polar regions  Greenland – 1.7 million km2  Antarctica – 13.9 million km2  Makes the land flatter 8/119 Buried Snow Changes to Ice METU-GEOE 231 9/119  METU-GEOE 231 GLACIER MOVEMENT How Glaciers Move  Process of movement  Weight (gravity) pulls ice down  Melting at bottom aids lubrication  Speed  Slow: 0.5 m per year  Fast: 30 m per day  From a few cm to 3000 cm / day  Average: 25 cm per day  Faster in the center 10/119 Anatomy of A Glacier METU-GEOE 231 11/119  METU-GEOE 231 A Typical Glacial Advance and Retreat 12/119  METU-GEOE 231 Extent of major glaciers at the height of the last ice age (20,000 b.p.) 27% of the earth's land surfaces were covered by ice at that time https://www.constantinealexander.net/2012/04/confirming‐carbons‐climate‐effects.html 13/119  METU-GEOE 231 Maximum Extent of Pleistocene Glaciation - 1/3 of land surface https://slidetodoc.com/glacial‐processes‐and‐ landforms‐what‐is‐a‐glacier‐2/ Most recent glacial maximum peaked 18,000 years ago and is considered to have ended 10,000 B.P. https://slidetodoc.com/glacial‐processes‐and‐landforms‐what‐is‐a‐glacier‐2/ 14/119  METU-GEOE 231 Current Extent of Glaciation - about 10% of land surface https://slidetodoc.com/glacial‐processes‐and‐landforms‐what‐is‐a‐glacier‐2/ 15/119 Polar Ice METU-GEOE 231 Currently continental ice sheets cover Greenland and Antarctica 16/119  METU-GEOE 231 Glaciers: A Part of Two Basic Cycles in the Earth System Movement of Glacial Ice – driven by gravity  Types of glacial movements  Plastic flow – internal flow  Slipping along the ground  Zone of fracture  Uppermost 50 meters  Crevasses form in brittle ice 17/119 Glaciers Move by Basal Sliding and METU-GEOE 231 Internal Plastic Flow Glacier motion occurs from four processes, all driven by gravity:  basal sliding,  glacial quakes generating fractional movements of large sections of ice,  bed deformation, and  internal deformation 18/119  METU-GEOE 231 Glacier flow just by internal deformation  it is likely that rates of creep decrease with depth, with  fastest ice movement at the surface and  slowest (or no) ice movement  at the base and  at the valley sides,  where resistive stresses are highest (Jiskoot et al., 2011).  Ice deforms because it is plastic.  If large stresses are applied it can crack in a brittle manner (forming crevasses or calving ice bergs). https://www.antarcticglaciers.org/glacier‐processes/glacier‐flow‐2/glacier‐flow/ 19/119  METU-GEOE 231 Basal Sliding  Glaciers can slide because ice melts under pressure, resulting in a film of water at the ice-bed interface.  This can facilitate decoupling and enhance fast ice flow.  If the glacier bed is rough, with many bumps and obstacles, this increases melting and ice flow. This process is known as regelation.  If water pressures become high enough, cavities can form at the ice-bed interface, causing sliding with bed separation.  This reduces basal friction and allows faster ice flow.  Sliding velocity is controlled by basal shear stress and effective pressure, which is the difference between ice overburden pressure and water pressure (Jiskoot et al., 2011). https://www.antarcticglaciers.org/glacier‐processes/glacier‐flow‐2/glacier‐flow/ 20/119 Glaciers: A Part of Two Basic Cycles METU-GEOE 231 in the Earth System  Zone of accumulation – the area where a glacier forms  Zone of wastage – the area where there is a net loss due to melting https://www.antarcticglaciers.org/wp‐content/uploads/2012/08/fs20093046_fig03.png 21/119 METU-GEOE 231 22/119 The Glacial Budget METU-GEOE 231 23/119  METU-GEOE 231  A crevasse is a deep crack, crevice or fissure, found in an ice sheet or glacier, or earth.  Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement.  The resulting intensity of the shear stress causes a breakage along the faces. 24/119  METU-GEOE 231 https://en.wikipedia.org/wiki/Crevasse#/media/File:Parque_estat al_Chugach,_Alaska,_Estados_Unidos,_2017‐08‐22,_DD_94.jpg https://en.wikipedia.org/wiki/Crevasse#/media/File:Crevass e‐Tangra‐Mountains.jpg 25/119 METU-GEOE 231 26/119 Glaciers: A Part of Two Basic Cycles METU-GEOE 231 in the Earth System Glaciers erode by quarrying, is a glacial  Plucking – lifting of rock blocks phenomenon that is responsible for the erosion and transportation  Abrasion of individual pieces of bedrock”  Rock flour (pulverized rock)  Striations (grooves in the bedrock) O’Sullivan et al. 2018 https://en.wikipedia.org/wiki/Plucking_(glaciation)#/ media/File:Glacial_Tarn_Formation_EN.svg 27/119 Erosional Landforms Created by (Alpine) Glacial Erosion METU-GEOE 231  Glacial Trough – long, U-shaped valleys that were carved out by glaciers that have since receded or disappeared [or glaciated valleys]  Hanging Valley – Large valley glacier systems consist of numerous cirques and smaller valley glaciers that feed ice into a large trunk glacier. Because of its greater ice discharge, the trunk glacier has greater erosive capability in its middle and lower reaches than smaller tributary glaciers.  Cirque – a bowl-shaped depression on the side of or near mountains, carved by the base of a glacier as it erodes the landscape.  Arête – a narrow ridge of rock which separates two valleys. It is typically formed when two glaciers erode parallel U-shaped valleys  Horn – results when glaciers erode three or more arêtes, usually forming a sharp-edged peak.  Fjord – a long, narrow inlet with steep sides or cliffs, created by a glacier  Tarn – is a proglacial mountain lake, pond or pool, formed in a cirque excavated by a glacier [or corrie loch]  Poter noster - one of a series of glacial lakes connected by a single stream or a braided stream system. 28/119  METU-GEOE 231 Erosional Landforms Created by (Alpine) Glacial Erosion 29/119 Glaciers METU-GEOE 231 The Matterhorn in the Swiss Alps 30/119 Cirques, Colorado METU-GEOE 231 a bowl-shaped depression on the side of or near mountains, carved by the base of a glacier as it erodes the landscape. 31/119 The Mother of All Cirques, Mount Everest METU-GEOE 231 32/119  METU-GEOE 231 Landforms created by glacial erosion Fjords of Norway a long, narrow inlet with steep sides or cliffs, created by a glacier 33/119 Landforms created by glacial erosion METU-GEOE 231 Fjords of Norway 34/119 Glacial Deposits METU-GEOE 231 Glacial Drift – A general term applied to all rock material (clay, silt, sand, gravel, boulders) transported by a glacier and deposited directly by or from the ice, or by running water emanating from a glacier. Types of Glacial Drift  Till (Moraine) – material that is deposited directly by ice  Stratified Drift – sediment deposited by meltwater Moraine – any accumulation of unconsolidated debris (regolith and rock) that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice sheet. Stratified Drift - predominantly sorted sediment laid down by or in meltwater from glaciers and includes sand, gravel, silt, and clay arranged in layers. 35/119 Moraines METU-GEOE 231  Ground moraine – an irregular blanket of till deposited under a glacier.  Tterminal moraine – a ridge-like accumulation of glacial debris pushed forward by the leading glacial snout and dumped at the outermost edge of any given ice advance. 36/119  METU-GEOE 231 sharp-crested piles of glacially-transported rocks and debris that are dropped by the ice as it melts. They form only in the ablation zone of a glacier (where more ice is melting than is accumulating as snow each year) 37/119  METU-GEOE 231 secondary terminal moraine deposited during a temporary glacial standstill. 38/119  METU-GEOE 231 ridge-like accumulation of glacial debris pushed forward by the leading glacial snout and dumped at the outermost edge of any given ice advance. It curves convexly down the valley and may extend up the sides as lateral moraines. 39/119 Continental Glaciers or Ice Sheets METU-GEOE 231 Kettles – when a block of stagnant ice (a serac) detaches from the glacier. Eventually, it becomes wholly or partially buried in sediment and slowly melts, leaving behind a pit. In many cases, water begins fills the depression and forms a pond or lake—a kettle. 40/119 Continental Glaciers or Ice Sheets METU-GEOE 231 Eskers – ridges made of sands and gravels, deposited by glacial meltwater flowing through tunnels within and underneath glaciers, or through meltwater channels on top of glaciers. Over time, the channel or tunnel gets filled up with sediments. 41/119 Continental Glaciers or Ice Sheets METU-GEOE 231 Drumlins – elongated, teardrop-shaped hills of rock, sand, and gravel that formed under moving glacier ice. They can be up to 2 kilometers 42/119 Continental Glaciers or Ice Sheets METU-GEOE 231 Outwash Plains occur in front of melting glaciers. They are expansive, generally flat areas that are dominated by braided rivers when the glacier is actively melting. This means that the sediment is typically finest farthest away from the glacier. Outwash plains can extend for miles beyond the glacier margin. 43/119  Glaciers METU-GEOE 231 Close-up view of the boulder Glacial till is typically unstratified and unsorted 44/119 Glaciers METU-GEOE 231 TILL (Unsorted debris) 45/119  METU-GEOE 231 Glacial Deposits Moraines – layers or ridges of till  Lateral  Medial  End  Ground Glacial Depositional Features  Outwash plain, or valley train  Kettles  Drumlins  Eskers  Kames 46/119  METU-GEOE 231 Glacial Deposits  Outwash plains: broad flat areas in front of glaciers (usually prairies or farmland today)  Eskers: long winding ridges where material was deposited in tunnels within glacier 47/119 Glacial Deposits METU-GEOE 231 Stratified and sorted sediments deposited by glacial outwash water 48/119 Glacial Deposits METU-GEOE 231 Drumlins – long smooth canoe - shaped hills made of till produced when advancing glaciers have run over earlier glacial moraines. 49/119 Glacial Deposits METU-GEOE 231 A Drumlin in Upstate New York 50/119 Glacial Deposits METU-GEOE 231  Kames – Small cone shaped hills of sand and gravel from streams on top of glaciers  Kettles & Tarns – Circular hollows on terminal moraines and outwash plains formed from large blocks of ice settling out and melting. The water from ice melt left behind forms the kettles tarns (small lakes)  Deltas – When glacial streams empty into lakes. 51/119 Glacial Deposits METU-GEOE 231 Kame 52/119 METU-GEOE 231 53/119  METU-GEOE 231 Kettle Lakes 54/119  METU-GEOE 231 Glacial Depositional Features 55/119  METU-GEOE 231 Glacial Depositional Features 56/119 Glaciers of the Past METU-GEOE 231 Ice Age  Began 2 to 3 million years ago  Division of geological time is called the Pleistocene epoch  Ice covered 30% of Earth's land area Maximum extent of ice during the Ice Age 57/119 Glaciers of the Past METU-GEOE 231 Indirect Effects of Ice Age Glaciers  Migration of animals and plants  Rebounding upward of the crust  Worldwide change in sea level  Climatic changes Causes of Glaciation  Successful theory must account for  Cooling of Earth, as well as  Short-term climatic changes  Proposed Possible Causes: Plate tectonics  Continents were arranged differently  Changes in oceanic circulation 58/119 The Ice Age METU-GEOE 231 1. Motions of tectonic plates brought land- mass to high latitudes 2. Volcanic activity produced dust that blocks solar radiation 3. Decrease in Sun’s energy output 4. Change in atmospheric composition; reduction in greenhouse gases 59/119 The Ice Age METU-GEOE 231 Causes of Glaciation Proposed possible causes: Variations in Earth's Orbit  Milankovitch Hypothesis  Shape (eccentricity) of Earth's orbit varies  Angle of Earth's axis (obliquity) changes  Axis wobbles (precession)  Changes in climate over the past several hundred thousand years are closely associated with variations in Earth's orbit. 60/119  The Ice Age METU-GEOE 231 Possible Causes of Glaciation Cycles Astronomical Hypothesis: explanation for glaciations and interglaciations based on cyclic variations in the solar energy received at the Earth’s surface 61/119  METU-GEOE 231 DESERT ENVIRONMENT & LAND FORMS 62/119  METU-GEOE 231 Definition of Desert  A desert is an area with less than 25 cm of annual precipitation  aridity index = potential evaporation/precipitation greater than 4.0  Deserts may be cold, temperate or hot. All major continents have one type of desert or the other. 63/119  METU-GEOE 231 Types of Deserts  Subtropical Desert – 30o Latitude  Deserts on Leeward side of major Mountain ranges  Interior Deserts- center of continents far from ocean  Coastal desert- prevailing onshore wind cooled by cold ocean current  Polar deserts- extremely cold and dry 64/119  METU-GEOE 231 This is Namibia where desert meets water https://www.facebook.com/Geo.sy.111/photo s/a.1828841247172265/4929215493801476/ 65/119  METU-GEOE 231 Coriolis “turns” them The Major Wind Cells The Coriolis Effect describes the turn of the wind to the right in the Northern Hemisphere caused by earth's rotation. 66/119 Subtropical Deserts +/- 30o latitude METU-GEOE 231 A subtropical desert is a type of ecosystem, or biome that is characterized by high temperatures, very low precipitation and warm soils. Sahara 67/119 A Rain‐Shadow Desert METU-GEOE 231 These produce clouds and rainfall on the windward side of the mountains, but the leeward side stays rain shadowed and extremely dry 68/119  Ocean-Current Desert METU-GEOE 231 Cold ocean currents have a direct effect on desert formation in west coast regions of the tropical and subtropical continents 69/119 Also Interior and Polar Deserts METU-GEOE 231 70/119 Desert Landscape (Features) METU-GEOE 231 Weathering and desert streams create Desert features  Weathering in Desert is mostly mechanical A little chemical weathering produces manganese and iron-oxide stains, called desert vanish  Stream Erosion Arroyo – channel with water during periods of high discharge but dry most part of the year Pediments – large-scale gently inclined surfaces Inselberg – steep-sided knob of durable rock Playa – dry lake bed 71/119 Desert Landforms Produced By Water METU-GEOE 231 72/119  METU-GEOE 231 Uluru (Ayers Rock) Inselberg 73/119 Geologic Processes in Arid Climates METU-GEOE 231 Weathering  Not as effective as in humid regions  Mechanical weathering forms unaltered rock and mineral fragments  Some chemical weathering does occur  Clay forms  Thin soil forms Most erosional work in a desert is done by running water  Flow only during periods of rainfall and often occurs as heavy showers  Causes flash floods  Streams are dry most of the time  Poorly integrated drainage  Desert streams are said to be ephemeral  Different names are used for desert streams including wash, arroyo, wadi, donga, and nullah. 74/119 A dry stream channel in the desert METU-GEOE 231 75/119 The same stream channel following heavy rainfall METU-GEOE 231 76/119 Playas METU-GEOE 231 also called pan, flat, or dry lake, flat-bottom depression found in interior desert basins and adjacent to coasts within arid and semiarid regions, periodically covered by water that slowly filtrates into the ground water system or evaporates into the atmosphere, causing the deposition of salt, sand, and mud along the bottom and around the edges of the depression. 77/119 Playas METU-GEOE 231 78/119 A Playa in Death Valley, California METU-GEOE 231 79/119  METU-GEOE 231 Swimmers in hypersaline Dead Sea Evaporite deposits indicate a dry climate in the geologic record 80/119  METU-GEOE 231 Transport By Wind  No dissolved load  Suspended Load- most consist of dust (silt, clay, pollen, bacteria, salt crystals, etc.)  Bed Load- sediments moved along or near the ground Rolling or saltation- bed loads lifted off the ground momentarily due to force of collision with other grains 81/119 Transport of Wind-Borne Sediment METU-GEOE 231 Suspended Load Transports Sahara sediment to Caribbean and Amazon Rain Forest 82/119 Work of Winds METU-GEOE 231 Erosion by Wind  Deflation – wind removes finer particles from the surface  Desert pavement – layer of pebbles left behind after deflation  Abrasion – sand blasting  Ventifacts – wind-shaped stones with sharp-edge faces  Yardangs – streamlined desert ridges 83/119 Wind Erosion METU-GEOE 231  Deflation Lifting of loose material Produces  Blowouts  Desert pavement  Abrasion – mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, Abrasion by Glaciers waves, gravity, running water or erosion. Abrasion by Wind (Yardang) Abrasion by Waves 84/119 Formation of a Desert Blowout METU-GEOE 231 sandy depressions in a sand dune ecosystem (psammasere) caused by the removal of sediments by wind. 85/119 Formation of Desert Pavement METU-GEOE 231 desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. They typically top alluvial fans. 86/119 Blowout Caused by Deflation METU-GEOE 231 erosion by wind of loose material from flat areas of dry, uncemented sediments such as those occurring in deserts, dry lake beds, floodplains, and glacial outwash plains. 87/119 Desert Pavements: Erosion METU-GEOE 231 gradual removal of sand and other fine particles by the wind and intermittent rains leaving behind the large fragments. The larger rock particles are shaken into place by actions of different agents such as rain, wind, gravity, and animals. 88/119 Desert Pavements METU-GEOE 231 89/119 Desert Pavements METU-GEOE 231 90/119 Desert Pavements METU-GEOE 231 These make good landing strips Source: Martin Miller 91/119 Desert Varnish slows infiltration METU-GEOE 231 Causes Flash Floods Desert varnish is the thin red-to-black coating found on exposed rock surfaces in arid regions. Varnish is composed of clay minerals, oxides and hydroxides of manganese and/or iron, as well as other particles such as sand grains and trace elements. 92/119  METU-GEOE 231 Inselbergs in southern California 93/119 Yardangs METU-GEOE 231 Remnants of Wind Abrasion in addition to occasional flash flood erosion (surface grains are frosted) 94/119 Yardangs METU-GEOE 231 White Desert, Egypt 95/119 Origin of Ventifacts METU-GEOE 231 (also wind-faceted stone, windkanter) is a rock that has been abraded, pitted, etched, grooved, or polished by wind- driven sand or ice crystals. 96/119 Origin of Ventifacts METU-GEOE 231 Wind 97/119 Types of Wind Deposits METU-GEOE 231 Sand Dunes  Mounds and ridges of sand formed from the wind's bed load  Characteristic features  Slip face – the leeward slope of the dune  Cross beds – sloping layers of sand in the dune Types of Sand Dunes  Barchan dunes  Transverse dunes  Longitudinal dunes  Parabolic dunes  Star dunes 98/119 Beach Sand Dunes METU-GEOE 231  Reduced wind velocity results in sediments deposition  Dunes are hills of loose wind-born sand Size, shape, and orientation of dune are determined by available sand, vegetation, and wind. 99/119 Deposition of Wind’s Bed Load METU-GEOE 231 Rain – Shadow Desert in Lee Of Mountains 100/119 Large-Scale Dunes (Gobi Desert) METU-GEOE 231 101/119 Formation of Sand Dunes METU-GEOE 231 Just like ripples in a stream 102/119 Formation of Sand Dunes METU-GEOE 231 103/119 Formation of Sand Dunes METU-GEOE 231 104/119  METU-GEOE 231 Deposition and Dune Types Dune Types  Transverse – ridges that are perpendicular to prevailing wind direction  Longitudinal – ridges that are parallel to prevailing wind direction  Barchans – crescent-shaped with horns pointing downwind  Horseshoe (Parabolic) – crescent-shaped with horns pointing upwind  Star – winds from three or more directions 105/119 Deposition and Dune Types METU-GEOE 231 106/119 Transverse Dunes METU-GEOE 231 ridges that are perpendicular to prevailing wind direction 107/119 Transverse Dunes METU-GEOE 231 108/119 Longitudinal Dunes METU-GEOE 231 ridges that are parallel to prevailing wind direction 109/119 Longitudinal Dunes METU-GEOE 231 110/119 Barchan Dunes METU-GEOE 231 crescent-shaped with horns pointing downwind 111/119 Barchan Dunes in Baja California METU-GEOE 231 112/119 Parabolic Dunes METU-GEOE 231 Parabolic – crescent-shaped with horns pointing upwind 113/119 Star Dunes METU-GEOE 231 winds from three or more directions 114/119 Star Dunes METU-GEOE 231 115/119  METU-GEOE 231 Lithified Sand Dunes (Jurassic Navajo Sandstone) 116/119 Types of Wind Deposits METU-GEOE 231 Loess  Deposits of windblown silt  Extensive blanket deposits  Primary sources are deserts and glacial stratified drift Loess formed by windblown deposits of glacial outwash silt Loess from the Columbia River Basin 117/119  METU-GEOE 231 Desertification  Desertification- invasion of desert conditions into formerly non-desert areas  Drought and overpopulation are main causes  Signs  Lowering of water table  Marked reduction of water supply  Increased salinity in water and soil  Progressive destruction of native vegetation  Accelerated soil erosion 118/119  Map of the Sahel METU-GEOE 231 The Sahel is the ecoclimatic and biogeographic realm of transition in Africa between the Sahara to the north and the Sudanian savanna to the south. 119/119 Deserts METU-GEOE 231 Basin and Range: the evolution of a desert landscape  Uplifted crustal blocks  Interior drainage into basins produces  Alluvial fans and bajadas  Playas and playa lakes 120/119 Deserts METU-GEOE 231 Basin and Range: the evolution of a desert landscape  Erosion of mountain mass causes local relief to continually diminish  Eventually mountains are reduced to a few large bedrock knobs called inselbergs projecting above a sediment filled basin Landscape evolution in a mountainous desert – early stage 121/119 Deserts METU-GEOE 231 Landscape evolution in a mountainous desert – middle stage 122/119 Deserts METU-GEOE 231 Landscape evolution in a mountainous desert – late stage 123/119 Deserts METU-GEOE 231 Paria Canyon-Vermilion Cliffs, Arizona, formed by wind erosion in the Navajo Sandstone 124/119