Glaciers and Glaciation Lecture 13 PDF

,, 11,. -'!'_.. ,, ~ -- 11 ' l f '• l ' • Glacier □ A thick ice mass that forms over hundreds or thousands of years. □ It originates on land from the accumulation, compaction, recrystallization of snow. Source: h ttps:// www.metoffice.gov. uk/ learning/precipitation/ sno w HDA. Reyes...

,, 11,. -'!'_.. ,, ~ -- 11 ' l f '• l ' • Glacier □ A thick ice mass that forms over hundreds or thousands of years. □ It originates on land from the accumulation, compaction, recrystallization of snow. Source: h ttps:// www.metoffice.gov. uk/ learning/precipitation/ sno w HDA. Reyes \ and Source: https://a/askan rafting. com/t1.Qduct/glacier-b lue-kayak-scenicgrandview-train-t our/ ~ ...... I Principles of Geology • Valley (Alpine) Glacier □ These are moving ice masses Source: https://www. ency123. com/2015/03/glaciers-f or-kids-what-is-valleyglacier. htm l • HDA. Reyes I Principles of Geology • Ice Sheets □ A permanent layer of ice covering an extensive tract of land, especially a polar region. -"-",-,,-"",._ FIGURE 11.2 The only present-day conbn-enial ice sheets are lhose covering Greenland and Antarctica. The,r combined areas rep,esent almost 10 ~rcent ol E:anh's land area. • t,, f Greenland"s ice sheel occupies 1.7 millLon square 1 . ·,~1'. , ~ i; ·j\ ,. kfometers, or about80percent or the ii land. The area of the AntarctJc: Ice Sheel is almost 14 million square kilometers. Ice shelves occupy an adcf.tional 1.4 million square kilo mete~ adjacent to the Anta retie: Antarcbc Perw,&ula Ice Sheet. '\_ a- ---..;. ~ ,. Rosa Ice 1/ Shlllf-- 1 ,---7 \ HDA. Reyes I Principles of Geology . ~ • Souih) Pole Anlslctl~ - ,LaraonB ,~ Shelf • Ice shelves □ They are large, relatively flat masses of floating ice that extend seaward from the coast but remain attached to the land along one or more sides. Source: http://www.r ador.ro/2015 /08/05/gheta rii-se-topescde-doua-treiori-mairepededecat-in secolultrecut-video/ HDA. Reyes I Principles of Geology • Outlet Glaciers □ Tongues of ice flow down valleys extending outward from the margins of these larger ice masses Source: ht tps://com mons. wikime dia. org/wiki/ Out let_ glacie rs HDA. Reyes I Principles of Geology • Piedmont Glaciers □ Occupy broad lowlands at the bases of steep mountains and form when one or more valley glaciers emerge from the confining walls of mountain valleys. Source: http://uni.no /en/unic/imate/clima teservices/mar ginsgreenlandmarginsglacial-iceocean-andatmosphericdyn amics/ HDA. Reyes I Principles of Geology • Snowline □ The elevation above which snow remains throughout the year. □ Elevations above about 5000 meters. ~ ,..:::-;ci"""I HDA. Reyes I Principles of Geology Source: https://www. bookmundi.c om/moshi/tr ek-mt kilimanjaro lemoshoroute-viacrater-camp9861 • How glaciers formed? □ Firn □ deposits of granular recrystallized snow Once the thickness of ice and snow exceeds 50 meters (160 feet), the weight is sufficient to fuse firn into a solid mass of interlocking ice crystals. Glacial ice has now been formed. Source: https://com mans. wikime dia.org/wiki/ Fi/e:Firn ss 2 006.jpg HDA. Reyes I Principles of Geology • How glaciers move? □ Zone offracture - The upper- most brittle portion of glacier □ Crevasses -The cracks developed in the glaciers. Source: http://menta /floss.com/ar ticle/93624/ whatdifferencebetweencrevice-andcrevasse FIGURl: 11 ,7 A vertical cross section through a glacier illustrates ice movement. Glaoal movement rs di,,ided into two components_Relow about~ meters (160 feet), ice behaves plastically and Hows. In addition, the entire mas-. of ice may shde along t he ground. The ice rn ihe zone o f fracture is carried along • piggyback" !rtyle. Notice that tke rate of movement i, slowest at th.e base of the glacier, wkere frictional drag is greatest. HDA. Reyes I Principles of Geology • Budget of a Glacier □ Glacial Zone ✓ Zone of Accumulations Area where snow accumulates (Limit: Snowline). ✓ Zone of Wastage Below snowline where melting happens ✓ Calving The process of breaking off large glaciers that creates icebergs. HDA. Reyes I Principles of Geology ~ • 1 FlGURE 11.10 The ma.vtine separates the zone of.accumulation and the zone of wastage_ Above the1.nowbne, more soow fa.Hs each winter t:han melts each summer. Bela-N the sncmfifle, the snON from the previous winter comp~tely melts as does some of the underlying ice_ Whether the margin o f a glaoer advances, retreats. or remains statJonary depends on 1he balance between aca,mulauonandwastage ~~iiiii (ablation)_ 'INhen a glacier moves across irregular terrain, crevasses form in the brittle uppe< ponion_ • Budget of a Glacier □ Glacial budget is the balance, or lack of balance, between accumulation at the upper end of the glacier and loss at the lower end. This loss is termed ablation. Source: https://www. f/ickr. com/ph otos/bingha msaz85138/6 018607149/ Source: http://marconisociety.org/doubling-wireless-bandwidth/ HDA. Reyes I Principles of Geology • Glacial Erosion □ Glaciers erode the land primarily in two ways-plucking and abrasion. ✓ Plucking - occurs when meltwater penetrates the cracks and joints of bedrock beneath a glacier and freezes. ✓ Abrasion - As the ice and its load of rock fragments slide over bedrock, they function like sandpaper to smooth and polish the surface below and produces rock flour (glacial gristmill). •!• Glacial striations - When the ice at the bottom of a glacier contains large fragments of rock, long scratches and grooves. HDA. Reyes I Principles of Geology • Glacial Landforms FIGUllE -shaped vallay n .17 !;.ros,onal landfornis created by alp1no glaci=. Th<! unglac,ated landscape in pan A. ,s mod:fii,d by w11n@y glacioroa in Pllrl 8 . Afler the Ice recede&, In part C., tho ll>rniin looo very diifomrr1 thar, bef0<e 9laoat.ion rArr!Ce photo /rgm J~rrm E. P.1ttorson Co"ocoon. C,rquephcto byMarl, lvMer; A.Unglacl~ topography f"l;an iing v~«,:,y photo Wardeol5<.ipei.tod;I a. R90ian during period of mulm..., gtaclal'ion 0 . Glacillled topography HDA. Reyes I Principles of Geology qy John med.llill • Glacial Landforms □ Glaciated Valleys n,01atoe 1/; ✓ Glacial trough - U-shaped valley created by alpine glaciers. ✓ Hanging valleys tributary glaciers that are left standing above the main glacial trough. ✓ Pater noster lakes - depressions created by glacial movement through plucking which are filled with water. ✓ Cirque - bowl-shaped depression has precipitous walls on three sides but is open on the downvalley side. HDA. Reyes (a) hom ta,n ilfOIO cl tq"!O$ p;.,te, nostet lakos glacial trou; n (b) --- --.____ Source: http://thebritishgeographer.weebly.com/the-physica/characteristics-of-extreme-environments.html I Principles of Geology • Glacial Landforms □ Glaciated Valleys ✓ Glacial trough - U-shaped valley created by alpine glaciers. ✓ Hanging valleys tributary glaciers that are left standing above the main glacial trough. ✓ Pater noster lakes - depressions created by glacial movement through plucking which are filled with water. ✓ Cirque - bowl-shaped depression has precipitous walls on three sides but is open on the downvalley side. HDA. Reyes -- Source: https://alchetron.com/Paternoster-lake - - - ,;,; ~- • • Source: https://www.tes.com/lessons/ YTvjVJJObZ02Dgl1-10-i-ghiaccial I Principles of Geology • med.llill Glacial Landforms □ Glaciated Valleys n,01atoe 1/; ✓ Tarn - A small lake formed in the cirque after the glacier has melted away. ✓ Fiords - deep, often spectacular, steep-sided inlets of the sea that are present at high latitudes where mountains are adjacent to the ocean. They are drowned glacial troughs that became submerged as the ice left the valley and sea level rose following the Ice Age. (a) hom ta,n ilfOIO cl tq"!O$ p;.,te, nostet lakos glacial trou; n (b) --- --.____ Source: http://thebritishgeographer.weebly.com/the-physica/characteristics-of-extreme-environments.html HDA. Reyes I Principles of Geology • Glacial Landforms □ Glaciated Valleys ✓ Tarn - A small lake formed in the cirque after the glacier has melted away. ✓ Fiords - deep, often spectacular, steep-sided inlets of the sea that are present at high latitudes where mountains are adjacent to the ocean. They are drowned glacial troughs that became submerged as the ice left the valley and sea level rose following the Ice Age. Source: https;//www.swisseduc.ch/glaciers/glossary/cwm-en. html d HDA. Reyes I Principles of Geology • med.llill Glacial Landforms □ Glaciated Valleys n,01atoe 1/; ✓ Aretes sinuous, sharp-edged ridges. ✓ Horns - sharp, pyramid like peaks (a) hom ta,n ilfOIO cl tq"!O$ p;.,te, nostet lakos glacial trou;n --- (b) --.____ Source: http://thebritishgeographer.weebly.com/the-physica/characteristics-of-extreme-environments.html HDA. Reyes I Principles of Geology • Glacial Landforms □ Glaciated Valleys ✓ Aretes sinuous, sharp-edged ridges. ✓ Horns - sharp, pyramid like peaks Sou rceh ttps :/I al/you needtokn o wab outgla ciers. wee b ly. com/g/ acial-erosion. html HDA. Reyes Source: https://www.thoughtco.com/glacier-picture-gallery- 4122871 I Principles of Geology • Glacial Landforms □ Glaciated Valleys ✓ Roches Mountonnees •••• An asymmetrical knob of bedrock •••• It is formed when glacial abrasion smoothes the gentle slope facing the oncoming ice sheet and plucking steepens the National Par'I-, California The gentle slop& abraded and the ~l.eep side wa~ pluded opposite side as the ice wa1 The ,ce movoo from nght to lefL {Pharo J Tarbucij rides over the knob. •••• Indicate the direction of glacial flow, because the gentler slope is generally on the side from which the ice advanced. HDA. Reyes I Principles of Geology - FIGURE. 11.21 Roche moutonn""' 1n Yos.,mite by I, • Glacial Deposits □ Glacial drift - an all-embracing term for sediments of glacial origin, no matter how, where, or in what form they were deposited ✓ Till- Materials deposited directly by the glacier. ✓ Ti/lite - Consolidated tills. ✓ Stratified drift- Sediments laid down by glacial meltwater. ✓ Glacial erratics - boulders found in the till or lying free. HDA. Reyes I Principles of Geology • Glacial Deposits □ Moraines - layers or ridges of till □ Outwash Plains - ramplike surface composed of stratified drift is built adjacent to the downstream edge of most end mora ines. □ Valley Train - outwash plain deposit largely confined to a mountain valley. □ Kettles - pockmarked with basins or depressions. Source: http://www. geo. mtu. edu/KeweenawGeohe ritage/Glaciers/Kett/es .html HDA. Reyes I Principles of Geology • Effects of glaciers □ Crustal Subsidence and Rebound □ Sea-Level Changes Source: http://www. reporting c/imatescience.com/2 016/05/09/behaviourassumptions/ HDA. Reyes I Principles of Geology • Effects of glaciers □ Ice Age ✓ ltflACal' Pliestocene Epoch DAWN tr. DINOSAURS _,ll,IUl.t.MTa .. l'IUlfHa"t'... IU.~~ """'"·"-~" HDA. Reyes I Principles of Geology • Causes of Glaciation □ Plate Tectonics □ Variations in Earth's Orbit ► Milankovitch formulated a comprehensive mathematical model based on the following elements 1. Variations in the shape (eccentricity) of Earth's orbit about the Sun; 2. Changes in obliquity; that is, changes in the angle that the axis makes with the plane of Earth's orbit; and 3. The wobbling of Earth's axis, called .,. . precession . HDA. Reyes I Principles of Geology Pllnl ~ Eanh,'s orhi e. • Causes of Glaciation □ Other Factors ► Degassing (Green House Effect) HDA. Reyes I Principles of Geology Lutgens, F., Tarbuck, E. and Tasa, D. (2012). Essentials of Geology Eleventh Edition. Upper Saddle River, New Jersey: Pearson Prentice Hall. HDA. Reyes I Principles of Geology