Week 07 Glacial Erosion, Continental Glaciation, Mountain Glaciers PDF

Physical Geography: Glacial Erosion, Continental Glaciation, Mountain Glaciers 10/14/2024-10/16/2024 PROFESSOR PETE PULEO 1 Glacial Erosion and Deposition 2 Learning Objectives Explain how glaciers act as important agents of landscape formation and d...

Physical Geography: Glacial Erosion, Continental Glaciation, Mountain Glaciers 10/14/2024-10/16/2024 PROFESSOR PETE PULEO 1 Glacial Erosion and Deposition 2 Learning Objectives Explain how glaciers act as important agents of landscape formation and discuss the different categories of glaciers Give a brief overview of how past glaciation has influenced Earth’s surface over large areas of the continents Describe the formation of glacier ice and its movement through the glacial system Summarize how glaciers shape the landscape through erosion and deposition 3 What is the Cryosphere? The major component of the Earth system that consists of frozen water 4  Glacier Body of ice on land that is in motion https://landsat.visibleearth.nasa.gov/view.php?id=144376 5  Glaciers vs. Ice Sheets Glaciers: Ice Sheets: Present across the world, Present in only Greenland and particularly in cold, mountainous Antarctica regions Massive (>50,000 km2) Smaller body of moving ice https://nsidc.org/learn/parts-cryosphere/ice-sheets/ice-sheet-quick-facts 6 Glacier Snow -> Firn Formation Firn – Granular, compacted snow 7 Glacier Formation Scientist measuring depth and sampling layers of snow Why care about this? 8 Glacier Formation Scientist measuring depth and sampling layers of snow Why care about this? Compaction and density influences snow -> firn -> ice transformation 9 Glacier Formation Accumulation Zone – Area where ice volume is gained on a glacier Ablation Zone – Area where ice volume is lost on a glacier 10 Glacier Mass Change Accumulation > Ablation: Glacier increases in size Accumulation < Ablation: Glacier decreases in size 11  Glacier Equilibrium Equilibrium Line – The altitude at which accumulation rate and ablation rate are equal for a glacier https://commons.wvc.edu/rdawes/g101ocl/basics/glaciers.html 12 Glacier Growth and Retreat What influences where Accumulation Zone and Ablation Zone meet? 13 Glacier Growth and Retreat What influences where Accumulation Zone and Ablation Zone meet? Key factors are summer temperatures above freezing and amount of snowfall 14  Glacier Growth and Retreat https://www.coolgeography.co.uk/A- level/AQA/Year%2012/Cold%20environs/Systems/Glacial%20Systems.htm 15 Glacier Flow Ice moves from high elevation to low elevation due to gravity Ice moves from high pressure to low pressure 16 Glacier Movement Creep – Internal deformation of ice Sliding – Movement of entire glacier over rocks below 17 Glacier Movement Flow is fastest at upper central part of the glacier Flow is slowest at rock contact points 18 Glacier Movement Stress from glacier motion/deformation leads to cracks on the brittle ice surface known as crevasses 19  Glacier Movement Surge – Glacier movement associated with rapid flow at a much higher rate than average https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023JF007306 20  Temperature and Pressure https://www.researchgate.net/figure/Variation-of-the-melting-temperature-of- ice-with-pressure-Nordell-1990_fig12_44062059 21 https://www.coolgeography.co.uk/A- level/AQA/Year%2012/Cold%20environs/Systems/Glacial%20Systems.htm 22 Glacial Erosion Plucking – Fragments of bedrock are frozen into ice as it moves above 23 Glacial Erosion Abrasion – Rock fragments trapped in basal ice scour the bedrock surface Striations – Scratches made by plucked rocks that indicate direction of ice movement 24 Glacial Erosion Landform Roche Moutonnée – Asymmetrical mound formed by abrasion on one side and plucking on the other 25  Glaciers of the Past Glacial Periods – Times when Earth’s climate was cooler, and ice sheets were much more expansive ~20,000 years ago https://waglacialerratics.ess.washington.edu/science/ 26 Deglaciation Period of rapid retreat 27  Interglacial Period Relatively warm global climate with reduced global ice sheet volume Currently interglacial conditions, ice sheets only on Greenland and Antarctica https://svs.gsfc.nasa.gov/5099/ 28  Activity 1 Description Observe the figure and answer the following questions: 1) What is the relationship between temperature and CO2 concentrations during glacial- interglacial cycles? 2) What is the difference in CO2 concentrations between maximums in interglacial periods and maximums in glacial periods? 3) What is the difference in temperature between maximums in interglacial periods and maximums in glacial periods? 29  Activity 1 Solution 1) What is the relationship between temperature and CO2 concentrations during glacial-interglacial cycles? Tightly coupled or positively correlated. CO2 is a greenhouse gas, meaning it traps heat from the Sun on Earth. 30  Activity 1 Solution 2) What is the difference in CO2 concentrations between maximums in interglacial periods and maximums in glacial periods? Minimums: 180-190 ppm, Maximums: 270-300 ppm, Difference = 90-120 ppm 31  Activity 1 Solution 3) What is the difference in temperature between maximums in interglacial periods and maximums in glacial periods? Max = 5 to 8°C, Min = -3 to -4 °C, difference = 8-12°C 32 Landforms and Landscapes of Continental Glaciation 33 Learning Objectives Compare and contrast the contemporary continental ice sheets Identify typical landforms and landscapes produced by continental glaciers and discuss the glacial processes that formed them Briefly discuss the pluvial lakes that formed during glacial periods in the western United States 34 Antarctic Ice Sheet Subdivided into West and East 13 million km2 area (9% of global land) 60 m of global sea level rise 35 Antarctic Ice Sheet Flow Different sections flow in different directions Why? 36 Antarctic Ice Sheet Flow Different sections flow in different directions Why? Ice sheet altitude, pressure, and gravity 37 Greenland Ice Sheet ~1.6 million km2 area (1/8 Antarctic Ice Sheet) ~6-7 m global sea level rise if melted 38 Greenland Ice Sheet Flow Generally, from high to low elevation 39  Greenland Ice Sheet Flow Fastest surface flow near edges Dark blue indicates sections of the Greenland Ice Sheet https://www.researchgate.net/figure/a-Surface-velocity-map-of-the-Greenland- ice-sheet-highlighting-the-NEGIS-and-its_fig1_340017057 40  Continental Glacier Weight https://www.gfz-potsdam.de/en/section/earth-system-modelling/topics/solid- earth-dynamics/glazial-isostatic-adjustment-gia 41 Continental Glacier Flow Ice Streams – Zones of fast flowing ice near coasts What is it called when a glacier flows many times faster than average? 42 Continental Glacier Flow Ice Streams – Zones of fast flowing ice near coasts What is it called when a glacier flows many times faster than average? Surge! 43 Antarctic Ice Streams https://www.youtube.com/watch?v=KlDO0C8r_ws&t=25s 44 Ice Sheet Mass Change 45  Sea Level After Ice Sheet Melt https://www.nationalgeographic.com/magazine/article/rising-seas-ice-melt- new-shoreline-maps 46  Ice Shelves Floating extensions of an ice sheet that remain attached https://www.antarcticglaciers.org/glaciers-and-climate/changing- antarctica/shrinking-ice-shelves/ice-shelves/ 47  Calving Ice shelves breaking off into massive icebergs https://www.antarcticglaciers.org/glaciers-and-climate/changing- antarctica/shrinking-ice-shelves/ice-shelves/ 48 Past Continental Ice Sheets Caused by cooler climates in the past due to changes in Earth’s orbit and CO2 concentrations 49 Glacial Drift Sediments deposited by glaciers Broken into two main categories: 1) Till 2) Outwash 50 Till Poorly sorted sediment with grain sizes from clay to boulders deposited by glaciers 51 Outwash Well sorted sediments deposited by glacial meltwater, characterized by stratified layers 52  Erratics Boulders carried far from their source area by glaciers Erratic in Central Park, NYC https://paulhcleverley.com/2019/08/26/erratics-in-central-park-new-york/ 53 Moraine Ridge of glacial drift that marks the former outline of a glacier 54  Types of Moraines https://www.internetgeography.net/topics/which-landforms-result-from-moving- or-melting-ice/ 55  Drumlin Elliptical, steep-sided hill formed under ice https://planetearth.utsc.utoronto.ca/news/Drumlins_2021_09_20.html 56  Drumlin Formed as ice flows over bedrock and deposits till https://www.geo.mtu.edu/KeweenawGeoheritage/Glaciers/Drumlin.html 57 Drumlin What does this feature look like on a topographic map? 58 Drumlin What does this feature look like on a topographic map? 59 Esker Long, steep-sided, sinuous ridge 60  Esker Formed by meltwater flowing through a basal tunnel and filling with sediment https://commons.wikimedia.org/wiki/File:Esker_Formation.png 61 Kame A rounded hill of gravel and sand deposited by meltwater 62  Kame Form by water moving sediments that are deposited after melting https://physgeog.blogspot.com/2012/12/fluvioglacial-landforms-formaton- of.html 63 Kettle A depression often filled with water (kettle lake) created by glaciers 64 65 Outwash Plain An area at the front of a glacier filled with meltwater fed braided streams and glacial sediments 66 Pluvial Lakes Bodies of water that accumulated because of greater moisture availability Driven by temperature (colder -> less evaporation) and atmospheric circulation changes from ice sheets 67 Pluvial Lakes US SW had cooler and wetter conditions in glacial times Lake Bonneville was largest (1000 ft deep and size of Lake Michigan) Have mostly disappeared due to evaporation today (Great Salt Lake is an exception) 68 Activity 2 Description Work independently to draw and describe the formation of the following features. Then, get with a partner to share your drawings and discuss how they form. 1) Drumlin 2) Esker 3) Moraine 4) Kame 5) Kettle 69 Activity 2 Solution 70 Activity 2 Solution 1) Drumlin – Forms from partial erosion and compression under ice 2) Esker – Forms from meltwater below a glacier flowing through a tunnel and depositing sediment 3) Moraine – Forms from glaciers moving and concentrating surface materials near its edges 4) Kame – Forms from a vertical hole in a glacier allowing meltwater flow and sediment to pile up 5) Kettle – Forms from an ice block leaving a depression after melting 71 Landforms and Landscapes of Mountain Glaciers 72 Learning Objectives Summarize the current distribution of mountain glaciers Describe the characteristic landforms produced by mountain glacier erosion Discuss the landforms produced by glacial deposition in mountain landscapes 73 Global Distribution of Mountain Glaciers 74 Global Distribution of Mountain Glaciers What makes these places ideal for glaciers? 75 Global Distribution of Mountain Glaciers What makes these places ideal for glaciers? High latitude -> Cold High elevation -> Cold Low summer temperatures (limits ablation) Some snowfall (increases accumulation) 76 Glacial Trough A U-shaped valley carved by a glacier Do not bend as much as river valleys 77  Truncated Spurs Ridges that descend towards a valley from a higher elevation that were eroded by glaciers https://en.wikipedia.org/wiki/Truncated_spur 78  Hanging Valleys Glacial troughs that hang above another lower elevation glacial trough https://en.wikipedia.org/wiki/Truncated_spur 79 Cirques Bowl-shaped, steep-sided depression in mountain from glacier 80 Horns Mountain peak created by adjacent cirques 81 Arêtes Sharp ridges separating cirques or glacial troughs 82 Rock Steps Step-like profiles in glacial landscapes from glacial erosion on rocks with different hardness and structure 83  Tarns Lakes inside of cirques https://www.nps.gov/articles/tarns.htm 84 Fjords Glacial troughs or valleys filled in with seawater 85  Rock Flour Fine grained sediment carried downslope by glaciers that can be moved by wind and water https://simple.wikipedia.org/wiki/Rock_flour 86  Types of Moraines https://www.internetgeography.net/topics/which-landforms-result-from-moving- or-melting-ice/ 87 Before Mountain Glaciation 88 During Mountain Glaciation 89 After Mountain Glaciation 90 Activity 3 Description Work independently to draw and describe the formation of the following terms. Then, get with a partner to improve your drawings and descriptions. 1) Cirques 2) Tarns 3) Horns 4) Arêtes 91 Activity 3 Solution 92 Activity 3 Solution 1) Cirques – Erosion from mountain glaciers creates bowl shape. 2) Tarns – Water fills in cirque. 3) Horns – Cirques lead to a single point on a mountain rising above the landscape. 4) Arêtes – Cirques and glacial troughs lead to a sharp ridge. 93  Multiple Choice Practice Qs Take ~ 1 minute to independently think about and write down an answer to the question on the board. Then, turn to a partner and discuss your reasoning for choosing that answer. Write a second answer after you have discussed your thoughts with a partner (its okay to write the same answer twice or change your answer, just be sure to have two answers per question). Finally, we will discuss the correct answer as a class. Be sure to have your name and date on top and hand in before you leave. 94 Question 1 Presently, continental glaciers or ice sheets exist in: A) Antarctica and Greenland only B) Antarctica, Greenland, and northern Canada C) Antarctica, Greenland, northern Canada, and Russia D) Antarctica only 95 Solution 1 Presently, continental glaciers or ice sheets exist in: A) Antarctica and Greenland only B) Antarctica, Greenland, and northern Canada C) Antarctica, Greenland, northern Canada, and Russia D) Antarctica only 96  Question 2 Most of the erosive work of glaciers is accomplished by: A) kettles B) erratics C) glacial sliding D) glacial creep 97  Solution 2 Most of the erosive work of glaciers is accomplished by: A) kettles B) erratics C) glacial sliding D) glacial creep 98  Question 3 If you see glacial sediment from a glacier that has some large clasts and is unsorted, it is likely: A) outwash B) till C) glacial flour D) associated with a drumlin 99  Solution 3 If you see glacial sediment from a glacier that has some large clasts and is unsorted, it is likely: A) outwash B) till C) glacial flour D) associated with a drumlin 100 Question 4 How do pluvial lakes relate to glaciation? A) They formed during glacial periods when continental glaciers blocked outlet rivers. B) They formed during glacial periods when precipitation was more abundant and evaporation rates were lower. C) They were carved out by continental glaciers. D) They were carved out by mountain glaciers. 101 Solution 4 How do pluvial lakes relate to glaciation? A) They formed during glacial periods when continental glaciers blocked outlet rivers. B) They formed during glacial periods when precipitation was more abundant and evaporation rates were lower. C) They were carved out by continental glaciers. D) They were carved out by mountain glaciers. 102 Question 5 A glacial trough that extends below sea level is a: A) marginal lake B) fjord C) hanging valley D) tarn 103 Solution 5 A glacial trough that extends below sea level is a: A) marginal lake B) fjord C) hanging valley D) tarn 104 Question 6 What is the typical shape of a valley that experienced substantial glaciation in only its upper region? A) U-shaped in both the upper region and the lower region B) V-shaped in both the upper region and the lower region C) U-shaped in the upper region and V-shaped in the lower region D) V-shaped in the upper region and U-shaped in the lower region 105 Solution 6 What is the typical shape of a valley that experienced substantial glaciation in only its upper region? A) U-shaped in both the upper region and the lower region B) V-shaped in both the upper region and the lower region C) U-shaped in the upper region and V-shaped in the lower region D) V-shaped in the upper region and U-shaped in the lower region 106