Study Guide for ESS 21 Exam 3 2021 Your primary sources of information are the lecture videos and questions, weekly quizzes, and discussion worksheets with the textbook used only for additional background on an optional basis. If a term or topic is in the textbook but we did not mention it at all in the lectures then you will not need to know it for the midterm. Below is a list of the important topics we have covered so far – concentrate on understanding and applying your new knowledge rather than memorizing. I will give you formulae and I will not ask you to write out definitions (although they may come up in multiple choice questions). We will be using Respondus Lockdown Browser and Monitor to proctor the exam online – you will therefore need a working webcam and microphone. The exam will consist of a mixture of short answer and multiple choice questions within Canvas Quizzes. During the exam you can use as many paper notes as you like but you will not be allowed to use calculators, any other electronic devices, and you are not allowed to communicate with anyone else. Because no calculators are allowed, any math questions will be simple calculations that you can do in your head or on paper. From Lecture 14 – Formation of glaciers, ice caps and ice sheets – Be able to describe what land ice is and have a rough idea of where it is found – Be able to explain why land ice is important to climate and society – Be able to describe and explain the steps of how a glacier/ice sheet is formed – Be able to classify a glacier (based on temperature or shape) from a description or photo/diagram – Be able to explain how ice accumulates on a glacier and what factors affect accumulation – Be able to explain the different types of ablation, where they occur, and what factors affect them From Lecture 15 – Glacier Mass Balance – Be able to explain what the equilibrium line is – Be able to describe/explain/identify the zone of accumulation, zone of ablation and equilibrium line from photos, diagrams, or graphs – Be able to predict how the amount of accumulation vs ablation will affect the mass of the glacier and so whether it will advance or retreat – Be able to interpret graphs showing total accumulation, total ablation, and the resulting mass of ice over time for different areas of a glacier – Be able to explain how glacier mass balance is measured in the field and the challenges of doing this – Be able to describe/explain how glacier mass balance is measured remotely and the challenges of using each method – Be able to describe/explain how and why we use the terminus position of glaciers instead to estimate glacier mass changes – Be able to explain/predict how glaciers in different areas respond to climate change due to increased temperatures, more precipitation, feedback mechanisms From Lecture 16 – Glacier dynamics – Be able to explain how the driving stress is derived and predict how changes to the glacier will affect driving stress – For each type of glacier movement (basal sliding or internal deformation/creep) be able to describe/explain: o how it works o what type of glacier it will occur in and why o the factors that affect how fast the movement will be in each case From Lecture 17 – Glacier Dynamics – Be able to describe/explain/identify on diagrams: o the movement due to basal sliding o the movement due to internal deformation o zone of plastic flow and zone of rigid flow o where the fastest flow speed will occur – Be able to make predictions about how bed softness and bed roughness will affect glacier speed and thickness – Be able to describe/explain how water is supplied to the base of a glacier how and predict/interpret graphs of how glacier speed changes over time From Lecture 18 – Tidewater glaciers, ice shelves and icebergs – Be able to explain why tidewater glaciers can become unstable and can retreat a great distance in a short time – Be able to explain why ice shelves are important when considering sea level rise – Icebergs: o be able to explain how they form, how they move, and how/why they are monitored o be able to explain and use Archimedes Law to calculate/explain what percentage of an iceberg is above and below seawater From Lecture 19 – Glacial landscapes – Be able to explain how glaciers are able to erode the landscape – Be able to explain how the following landscape features form due to glacial erosion and identify them from photos/diagrams: o polished surfaces and striations o roche moutonnees o U-shaped valleys and fjords o hanging valleys o cirques and tarns o arêtes and horns – Be aware that glaciers pick up and transport sediment – Be able to explain how the following landscape features form due to glacial deposition and identify them from photos/diagrams: o moraines and lakes o erratic boulders o eskers ESS 21: On Thin Ice 2021 – Exam 3 Practice Questions Part A: Questions are worth 1 point each. 1. What is the value of angle Z on the diagram below? a. b. c. d. 2. Which of the following will NOT raise sea level when it melts? a. ice sheet b. cirque glacier c. iceberg α 90 90 + α 90 – α d. tidewater glaciers 3. A satellite emits a radio wave towards Earth’s surface which is 3000 km below. If the radio wave travels at 300,000 km/s, how long will it take the satellite to detect the reflected signal? a. 0.01 seconds b. 0.02 seconds c. 0.06 seconds d. 0.9 seconds 4. How will climate change affect glaciers? a. All glaciers will retreat due to warmer temperatures and more melting. b. Glaciers are likely to slow down due to greater amounts of water at their base. c. Ice shelves will becomes more stable due to cooler ocean temperatures around Antarctica. d. Most glaciers will retreat but a few will advance due to greater snowfall in winter. 5. What type of glacier is shown in the photo on the left? a. valley b. cirque c. ice shelf d. tidewater 6. Use the following information to calculate the density of an iceberg. Weight of iceberg = Buoyancy (weight of displaced seawater) Weight = volume x density x gravity Density of seawater = 1000 kg/m3 Percentage of iceberg under the water = 85% a. 150 kg/m3 b. 850 kg/m3 c. 1015 kg/m3 d. 1085 kg/m3 7. Which of the following statements is TRUE? a. Ice shelves rest on the ground surface so cause sea level to rise when they melt. b. The driving stress of a glacier will increase as the density of the ice decreases. c. The amount of multi-year sea ice in the Arctic has remained constant since the 1970s. d. Tidewater glaciers melt faster when more of the ice is exposed to seawater. 8. Which of the features below is a feature resulting from glacial deposition rather than glacial erosion? 9. Glaciers can erode sediments and rocks in two ways. Which of the following is NOT one of those ways? a. the ice itself grinds away rocks at the base of the glacier b. the rocks frozen into the ice at the base of the glacier act like sandpaper and grind away the solid rock below the glacier c. meltwater at the base of the glacier can refreeze in cracks and “pluck” rocks away from the ground surface 10. If a glacier mainly moves by internal deformation, what type of glacier is it? a. polar glacier b. ice shelf c. temperate glacier d. none of the above Part B: Answer the following short questions on this exam paper. The value of each question is in brackets. 1. Glacier mass balance (4) Image A shows a glacier from Alaska. a) Diagram B above is an outline of the glacier from Image A. Draw in the approximate position of the equilibrium line and label the zone of accumulation and zone of ablation. (2) b) On graph C above, draw a graph to show an approximate mass balance for this glacier. (1) c) Draw a graph of mass balance for the accumulation zone of a northern hemisphere glacier. Note that the graph time axis starts at the beginning of spring. (1) 2. Glacier dynamics (6) a) On the diagrams below, draw the position and shape of the pipe after a few months if: i) the glacier ONLY moved by basal sliding (1) ii) the glacier ONLY moved by internal deformation. (1) Basal sliding ONLY Internal deformation ONLY b) On the diagram on the right, draw a line to mark the boundary between the zone of plastic flow and zone of rigid flow and label each zone. (1) c) Complete the graphs below to show how the basal sliding rate and internal deformation rate of the glacier would vary over a year. This glacier is a temperate glacier and the discharge of water from under the glacier is shown in the bottom panel. (2) d) A glacier moving by basal sliding will move at different speeds depending on what is underneath it. Put the following in order from fastest (1) to slowest (3). (1) Sand _____ Rock _____ Water _____ 3. Glacial landscapes (3) Name 3 of the glacial features on the image below. (3) Lecture 14b – Formation of glaciers Learning outcomes • Be able to explain how land ice forms and where it is found • Be able to explain the importance of land ice to climate and society • Be able to identify glacier types from photos/diagrams based on their shape or temperature profile • Be able to describe and explain the accumulation and ablation processes that add or remove mass to the glacier What happens to the snowpack? • Snow can sublimate (turn from solid to gas) even at temperatures below 0 oC when exposed to sunlight, especially in dry and windy conditions • When temperatures rise e.g. in spring, snow melts to form water • Snow that does not melt or sublimate (turn into water vapor) can build up to form glaciers and ice sheets What would lead to growth of land ice? a) High obliquity (greater tilt) b) Low obliquity (less tilt) c) Either – it wouldn’t matter Origin of glaciers and land ice 1. more snow accumulates each winter than melts each summer: snow depth gradually increases 2. melting/sublimation and refreezing/deposition changes shape of crystals then pressure recrystallizes deep snow into denser ice with less air space Origin of glaciers and land ice 1. more snow accumulates each winter than melts each summer: snow depth gradually increases 2. melting/sublimation and refreezing/deposition changes shape of crystals then pressure recrystallizes deep snow into denser ice with less air space 3. eventually ice and snow become so thick that the pull of gravity causes the frozen mass to move: a glacier is formed What is a glacier? “a permanent body of ice, consisting largely of recrystallized snow, that shows evidence of slow downslope or outward movement due to its own weight” https://www.youtube.com/watch?v=6dFbuaz130c What is a glacier? “a permanent body of ice, consisting largely of recrystallized snow, that shows evidence of slow downslope or outward movement due to its own weight” Classified based on size/shape and base temperature Glaciers: Types based on shape 1. Cirque glacier – bowl-shaped depression 2. Valley glacier – when a cirque expands out and flows downward into a valley Glaciers: Types based on shape 3. Tidewater glaciers – when a valley glacier reaches the sea 4. Ice caps – cover 50,000 km2 , also extremely thick (up to 4km in Antarctica) covering almost all land features Glaciers: Types based on shape 6. Ice shelves – only found around Greenland and Antarctica today, occur where ice sheets extend over the sea and float on water, between 250m to 2.5km thick Glaciers: Types based on base temperature • Temperate glaciers = where atmospheric temperatures high enough for the glacial ice to be at or near its melting temperature • Polar glaciers = where atmospheric temperatures are so low all year that the glacial ice stays well below its melting temperature Glaciers: Types based on base temperature Which of these glaciers do you think will move faster? Why? a) Temperate b) Polar Lecture 14a – Land ice Learning outcomes • Be able to explain how land ice forms and where it is found • Be able to explain the importance of land ice to climate and society • Be able to identify glacier types from photos/diagrams based on their shape or temperature profile • Be able to describe and explain the accumulation and ablation processes that add or remove mass to the glacier Where is land ice? • 10% of land area on Earth is covered with land ice Quick geography review Where are the Andes on this map? A C B D E Quick geography review Importance of land ice to climate and society 1. Surface albedo – land ice covers over 10% of the Earth’s surface, even in summer, increasing Earth’s albedo Importance of land ice to climate and society 2. Melting of land ice (unlike sea ice) affects oceans by: • Increasing sea level • freshening the oceans in polar regions which may affect thermohaline circulation Importance of land ice to climate and society 3. Freshwater supply • Melting glaciers are vital in many places for maintaining streamflow through dry seasons to provide water for drinking, irrigation, industry, generating electricity, but can also cause dangerous floods • Especially important in Asian countries around Himalayas e.g. Pakistan, and South American countries around Andes e.g. Bolivia Quick geography review http://www.sporcle.com/games/g/world Lecture 14c – Accumulation vs ablation Learning outcomes • Be able to explain how land ice forms and where it is found • Be able to explain the importance of land ice to climate and society • Be able to identify glacier types from photos/diagrams based on their shape or temperature profile • Be able to describe and explain the accumulation and ablation processes that add or remove mass to the glacier What controls a glacier’s size and mass? • A “river” of ice flowing under its own weigh due to gravity • Accumulation is the addition of ice to the glacier • Ablation is the loss of ice from the glacier Ablation vs. Accumulation Which of these images represents an accumulation process for a glacier? A) B) C) Glaciers: Accumulation • Accumulation is the addition of ice to the glacier 1. Snowfall 2. Avalanching and blowing snow 3. Refreezing at base or on surface • Many factors, both local and distant, can affect accumulation: – Moisture source and distance from moisture source (closer to ocean = more snow) – Local temperature (too warm = rain, too cold = little snow) – Local wind – Topography Glaciers: Ablation • Ablation is the loss of ice from the glacier 1. Sublimation 2. Surface melting 3. Basal melting 4. Calving • Local factors affect ablation: – Sunlight and incoming radiation – Air temperatures – Ocean temperatures, where appropriate – Ground temperature Glaciers: Ablation 1. Sublimation • Especially common on tropical glaciers • Occurs where ice transforms to water vapor without going through the liquid stage • Forms spikes known as “penitentes” Source:http://thegreatoutdoorsbeautyandirony.tumblr.com/post/4875 7997575/harvestheart-penitentes-snow-like-knives Glaciers: Ablation 2. Surface Melting • Surface melting is a significant part of mass balance on mountain glaciers and the Greenland Ice Sheet
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