G102 Glaciers and Landslides NOS Week PDF

Week Preview 5 Key Ideas: Readings Must do: Videos in modules and some sort of interaction (with AI or take notes) This reading on the Concord Labs we will be doing, uncertainty and risk Should do: Sections 5.1-5.3 (Erosion/weathering), 11.5 Surface water from An Introduction to Geology Nice to...

Week Preview 5 Key Ideas: Readings Must do: Videos in modules and some sort of interaction (with AI or take notes) This reading on the Concord Labs we will be doing, uncertainty and risk Should do: Sections 5.1-5.3 (Erosion/weathering), 11.5 Surface water from An Introduction to Geology Nice to do: Sections 1.1, 1.2, 1.5, and 1.6 in An Introduction to Geology Flooding and Recurrence Intervals Stream Gauges Activities: Discussion: Your own Illusion of Explanatory Depth Experiment In Live Zoom Class In our live Zoom class, Videos Glaciers https://www.youtube.com/watch?v=vOAju-zNnrs Transcript: (00:00) [music] Glaciated regions of our planet (both those currently hosting glaciers, and those that hosted glaciers in the past) can be recognized by spectacular landforms, including broad U-shaped valleys with high relief, sharp ridges and peaks, and rounded bowls. In this video, we will discuss what glaciers are, where they are found, and how they sculpt the land. (00:25) What exactly IS a glacier? A glacier is a mass of compressed ice that has accumulated on land over many years of snowfall and that moves under its own weight. Ice found in the oceans is not considered a glacier and will not be discussed in this video. Glaciers are found where snow can collect in the winter and not fully melt in the summer. (00:49) As such, they are found at high elevations in the mountains, called alpine glaciers, or on continents near the north and south pole, called continental ice sheets. Alpine glaciers can be found in mountains all over the world including near the equator, but of course there they form only at the highest evaluations (4700 meters or higher above sea level). (01:12) The further north and south of the equator a mountain lies, the lower in elevation the glaciers can be maintained. For example, in Alaska, glaciers extend all the way to sea level. Within glaciated mountains, glaciers that fill the area between peaks in the center of the mountains are called ice fields. Valley glaciers extend out of those high elevations carving and filling U-shaped valleys, spilling out onto the flat land next to the mountains. (01:40) Where valley glaciers meet the ocean, they are called tidewater glaciers. If the end of a valley glacier extends outward onto a flat plain of land, not the ocean, it is called a piedmont glacier. Continental ice sheets are found in only two places on our planet: covering Greenland and Antarctica. These glaciers are many kilometers thick and are so heavy they depress the land beneath them isostatically, making that land sink into the underlying mantle much like a ship laden with cargo. (02:10) Remember, all glaciers will move under their own weight or they’re not considered glaciers. Alpine glaciers move downhill – continental ice sheets move outward from their center, where the mass of ice is greatest. Glaciers move either through plastic flow or by sliding on a layer of melt water at their base. (02:36) When glaciers flow plastically, it’s like silly putty – they remain solid, but the solid changes shape over time in response to the forces around it. During plastic flow, the edges of the glacier, where it encounters rock will move the slowest due to drag and friction. (02:52) The fastest movement occurs in the center of the glacier where it’s furthest from the rocks and has the least drag and friction. It’s similar in rivers – fastest flow in the center of the river, slowest along the sides where friction is greatest. Glaciers can be thought of as slow rivers of ice. The average speed of cold-based, nonsliding ice sheets is only a few meters a year. (03:18) The average speed of warm-based, sliding alpine glaciers on steep slopes is 300 meters or more a year (just less than 1 m/day). Surging glaciers, however, can move 100x faster than normal for several months to a few years. The most rapid surge known was in 1953 in northern Pakistan – 100 meters per day! (~12.5 m/hour or ½ meter a minute!) For continental ice sheets, the fastest moving ice stream is 34 meters per day – that’s 1.4 meters per hour! And it’s found in Greenland. (03:50) In addition to all glaciers moving continuously downhill or outward under their own weight, they can also advance or retreat (grow or shrink) over time depending on their snow supply. When more snow is added each year than lost (accumulation is greater than ablation), the glacier is advancing. (04:10) When there’s more snow lost than gained (ablation is greater than accumulation), the glacier is retreating. Whether a glacier is advancing or retreating, it still always moves, like a conveyor belt, outward or downward. Think of it as a slow escalator with steps added or removed with time, but continually cycling snow and anything that falls into that snow downward and outward. (04:38) As glaciers move, rocks are weathered, eroded, and deposited. Let’s look more closely at that work and the landforms that result. To review, the breaking down of rock chemically or physically is called weathering. The term erosion means the physical removal of rock fragments from one location and transport of them to another location. (05:00) The dropping of the rock into a new location is called deposition. Glaciers weather rock through two main methods: frost wedging and abrasion. When the base of glaciers melt, the melt water will migrate into cracks in the rocks and freeze. Frozen water takes up more space than liquid water, and the increased volume will wedge the cracks open. (05:24) Through a series of melt and freeze cycles, cracks will widen, and the rocks will be wedged apart. Glaciers pick up and carry away weathered pieces of rock by surrounding them with liquid water, which then freezes, trapping the rock within the glacier. These frozen fragments at the base of a glacier abrade and weather the rock over which they move, grinding them smooth or leaving striations in the rock surface. (05:53) In addition to carrying weathered rock frozen in its base and sides, glaciers also carry any weathered rocks that drop on their surfaces as they move through the landscape. All these pieces are continually conveyed downward to the toe of the glacier, where they are spit out or dropped. If the glacier is advancing, those deposits are also bulldozed or pushed forward in advance of the glacier. If the glacier is retreating, those deposits are left strewn across the ground. (06:14) The sediment carried by glaciers experiences no knocking about during transport and no chemical weathering. As such, glacial deposits can be identified by their angular-shaped grains of all sizes from the tiniest muds to boulders as large as houses. We characterize this wide range of grain sizes as poorly sorted. (06:40) We can see these larger house-sized grains left isolated on glacial plains long after the glaciers have left and the surrounding smaller sediment grains have been removed. These isolated large-grain remnants of glacial deposits are called glacial erratics. Piles of sediment dropped or spit out by glaciers are called moraines. Lateral moraines are the bulldozed piles of glacial sediment found along the edges of a valley glacier as it moves out of the mountains. Terminal moraines are the bulldozed piles found at the front or toe of an advancing (07:13) glacier. When a glacier retreats, the material it drops strewn across the land is called a ground moraine. When two glaciers meet and join, the lateral moraines that join up and combine and then continue to separate them are called medial moraines. When glaciers advance again over land they retreated from before, they can reshape the ground moraines into mounds known as drumlins. (07:38) If we look more closely at the toe of an active glacier, we can also see that melt water pours out from under its base into an outwash plain in front of the glacier. The sediments in this plain are carried by water and as such are smaller, more rounded, and well sorted. In many cases, the melt water can more easily erode the ice than the ground, so it carves its stream channel above ground as a tunnel or cave in the ice, depositing its bed load at its base, which is above the surrounding land. When the glacier retreats, these raised river beds, called eskers, can be (08:16) seen sinuously migrating across the landscape. Once the glaciers have completely retreated and disappeared, we can see the erosional landforms left behind. Valley glaciers carve downward into a U-shaped valley with steep almost vertical edges. At the tops of these valleys, glaciers erode upward and outward, carving bowls called cirques. (08:42) The bigger the glacier, the deeper the valley and cirque. Where small tributary valley glaciers joined up with larger main valley glaciers in the past, we see now these smaller tributary U-shaped valleys hanging over the larger valley below. We call these hanging valleys. Where two valley glaciers run parallel to each other, the rock in between can be carved upward and downward into sharp knife-like thin ridges, which we call arêtes. (09:15) And where many valley glaciers form outward from a single point, eroding downward, sideways and backwards, their respective cirques can collectively carve back and meet at a single sharp peak called a horn. When U-shaped valleys fill with ocean water, we call them fjords. This map shows you where glaciers are found today – covering roughly 10% of the land surface of the planet. (09:41) This map shows glacial coverage 20,000 years ago, during the last ice age, when glaciers advanced and covered 30% of the land surface. How do we know? We can see, map, and date the deposits these ice-age glaciers left behind: the moraines and the striations. We can also study sediments left behind in lakes and oceans. One of the major impacts of ice ages and a cooling planet is migration of flora and fauna. (10:07) In lake sediments, we see in ice-age sediments, spores from colder-adapted tree species. In ice-age sediments in the ocean, we find shells from cold-water species taking the place of what used to be warmer-water species. For example, in California, glacial erosion, moraines and striations are found in the high mountains. We find no evidence of glaciers covering the rest of the state. (10:29) But we do see evidence of ice-age impacts everywhere: lower sea level; fast-moving erosive rivers coming out of the Sierra with loads of sediment from glacial erosion; large lakes forming east of the Sierras; and migration of colder-adapted flora and fauna into the state and warmer-adapted ones out of the state. (10:55) San Francisco itself is built on the ancient sand dunes produced during the erosion of the Sierras by ice-age glaciers, when the Sacramento River dumped its sediment load 27 miles off the current coastline, which would have been sea level at the time, and winds blew that sand back over the continental shelf creating a massive sand dune province. Throughout most of Earth’s history the planet was much warmer than it is today. (11:18) About 2 million years ago, the start of the geologic period known as the Pleistocene, Earth cooled enough to form glaciers that alternately advanced across the land and then retreated backwards. When the glaciers advanced and grew, we referred to it as an Ice age. Intervening periods of time when Earth warmed and those glaciers retreated are called Interglacials. (11:40) What causes the cycles in and out of ice ages? Small perturbations in Earth’s climate that are reinforced over time with positive feedback. For example, when Earth’s tilt lessens, more sunlight reaches the poles throughout the year which melts more of the ice. Since ice reflects a lot of sunlight, less ice means less reflection and more absorption of sunlight. (12:04) More sunlight absorbed means more melting of the ice and so on in a positive feedback loop. Similarly, when Earth’s tilt increases, less sunlight will reach the poles during the winters, which allows more ice to form, which means more reflection of sunlight. Less sunlight means colder, which means more ice, more reflection, more cold, and so on. (12:29) There are plenty of additional factors that also contribute to surface cooling and warming. The amount of energy the sun radiates will fluctuate over time in cycles. The amount of greenhouse gases in our atmosphere changes with time. When sunlight passes through the atmosphere it does so as short-wavelength radiation, mostly ultraviolet (UV) and visible. This radiation heats the planet’s surface. (12:53) That heat radiates back out to the atmosphere, but as longer-wavelength IR or infrared radiation. Greenhouse gases in the atmosphere trap those longer IR waves and thereby keep the planet warm. More greenhouse gases, the warmer the climate. Important greenhouse gases on our planet are water, carbon dioxide, and methane. (13:17) Methane is produced by melting hydrates on the bottom of the seafloor, which happens when the oceans warm. It is also produced through livestock waste and decomposition in rice paddies. Carbon dioxide is produced through volcanism, decomposition, and fossil fuel burning. Ocean currents help distribute heat. When currents are trapped by land masses that move through plate tectonics, it can be harder to distribute heat across the planet, and some areas will be isolated and cooled. (13:48) That’s what happened to Antarctica about 30-40 million years ago when it separated from the remnants of Pangaea. As a result of this isolation, the ice age in Antarctica began at that time. Ice has covered Antarctica much longer than the first ice age appeared on all the other continents, 2 million years ago. All of these factors have combined to modify Earth’s climate and contribute to its alternating warming and cooling cycles during the past few million years. (14:18) As so much of our society is impacted by the results of rising temperatures – from melting glaciers, rising shorelines, and shifting climate zones which changes our agricultural locations, we need to be prepared for the consequences of these changes. Pause now. [music] [music] Mass Movement https://www.youtube.com/watch?v=q45i9JOdXCw Transcript: (00:00) [music] All the landforms on planet Earth are formed through a combination of tectonic forces that push the land up, erosional forces that work to tear it down, and rocks of varying character and resistance that impact the location of erosion. To review, the term erosion means the physical removal of rock fragments from one location and transport of them to another location. (00:28) The breaking down of the rock chemically or physically is called weathering. The dropping of the rock into a new location is called deposition. In the next few video tutorials, we will focus on various agents of erosion such as gravity, running water, waves, glaciers, and humans. For this video tutorial, we discuss the erosional agent of gravity. (00:52) Gravity is a force that pulls material downhill towards the center of the Earth. Any object sitting loosely on Earth’s surface will feel the pull of gravity and, unimpeded, will simply roll or side downhill. The heavier the object, the greater the force of gravity. Friction is the force that sticks loose material to a surface and needs to be overcome by the force of gravity before objects can move. (01:20) Friction depends on the materials involved and the angle of the slope. Rough material has more frictional stickiness. Smooth material, less so. When my hands are smooth, they slide by each other easily. If I cover them in rough gloves, it gets harder to slide them past each other. When I bend my hands, or let my fingers interfere, it’s harder to slide them past each other. (01:44) All of these are ways to increase the friction and keep objects from moving downhill. The weight of an object pushing against a surface will also contribute to friction. When I push my hands together tightly, it’s harder to slide them. This box, which is sitting on a hillside, is pulled toward the center of the Earth by the force of gravity, which is its weight. (02:05) If the box is not moving, the component of its weight that moves along the surface of the hill is matched by an equal but opposite force of friction. Notice what happens to the force of its weight along the surface as the hillside steepens, the arrow gets longer, meaning this surface component of the force is getting greater. (02:27) Once we get the hillside steep enough that the weight component along the surface is greater than the frictional force, the object will move downhill. We call downhill movements of weathered rock material on Earth’s surface mass movement, and we can classify the movement into a variety of types based on the type of material and the way it moves. The slowest type of mass movement is called creep and refers to the top soil or sediment slowly moving downhill on a day-to-day basis as it alternately expands and contracts through daily heating and cooling cycles. That motion, (03:00) while happening over distances of less than a millimeter, will overcome small frictional forces and allow a very small downhill movement each daily cycle. Cumulatively over many years, we see the top soil or sediment layer creeping its way downhill. Evidence that creep is occurring is visible when we see trees or fences on a slope bending downhill. (03:25) The fastest type of mass movement happens during a rock fall, which happens when cracks form on rock cliffs and eventually break off chunks of rock, which fall and collect at the base of the cliff in a pile known as a talus slope. These cracks can form through a number of processes, such as frost wedging and exfoliation. (03:46) For more information on the physical weathering processes, watch the video tutorial on Weathering. If a large number of rocks fall at the same time they can trap and ride atop a layer of air, which greatly reduces friction and allows them to move at speeds over 200 miles an hour. (04:10) We call these movements rock avalanches, and because of their great speed, they can travel great distances, even up and over ridges. Rock falls and rock avalanches pose a considerable threat to communities that live in the mountains. When a layer of rocks slides downhill along a planar surface, usually a rock bedding contact, fault, or foliation plane, it’s called a slide. (04:34) Slides can be triggered when water runs down along the bedding planes, reducing friction between them or when the base of the rock bed above the plane is excavated and thus is no longer supported. When material on the hillside moves downhill along a curved surface, it’s called a slump – think about what happens when you slump down in a chair. (04:55) Water can increase the likelihood of all these types of mass movement because it both reduces friction and adds weight. The more weight, the greater the force of gravity on the hillside. A little bit of water causes small particles to stick together, much like when you build sand castles on a beach. (05:13) Too much, however, and it pushes them apart. When water content increases enough, it can cause the surface material to liquefy and flow. These type of mass movements where water content is high are called flows. Given enough time, all hillsides will eventually fail and be eroded. What makes a particular hillside more likely than others to fail? What are some things you can look at for example if you’re looking to buy property and want to know its stability? First look at the steepness of the hillside. The gentler the slope, (05:46) the better. Then look at the rocks and material that make up the slope. The more solid the rock, the better. Loose, unconsolidated sediments or soils will be most likely to slump or slide. Then look at the geologic structure of the hillside. If there are bedding, foliation, or fault planes, are they parallel to the hillside? If so, they’re more likely to fail than those that are perpendicular to the hillside. (06:15) Is there a way for water that penetrates the hillside to easily flow out? Does it sit atop any ponds? Are there any springs? Water adds weight, so the more easily water can hit the surface and safely run off, the better. Finally, look at the vegetation. Plants with roots can help keep soils more compacted and connected, especially if the roots are deep. What are some triggers that could start mass movement on a susceptible hillside? When the base of a rock bed is excavated, it loses its support. (06:47) Excavation can happen during building of highways or roads or houses, or when rivers flood. Weight added to the top of a hillside will increase the force pushing downhill. Weight is added when houses are built on the top of the hill or when excavated sediment is piled up on the top of the hillside. Heavy rains or water leaks from reservoirs or homes at the top of a hillside can reduce friction and add weight to the hillside. (07:16) A common trigger for mass movement in California is what happens when heavy rains first appear in an area that experienced a fire in the previous year and had its vegetation removed. Finally, a large shaking of the ground, like in an earthquake or explosion or through heavy foot traffic crossing a hillside, can trigger a mass movement. In the state of California, mass movements cause the greatest financial and human impact of any natural disaster. (07:42) It’s a good idea to pay attention to the stability of hillsides when building structures, communities, and hiking trails. Pause now. [music] My Landslide type of movement lecture Hey! Welcome, students. This is a mini lecture on mass movement, also known as mass wasting or landslides. Mass movement is defined as the downward movement of soil or rock due to the effects of gravity alone. In mass movements, we don’t need water or wind as driving forces. When discussing geology, we use specific terms: for processes involving water, we say “fluvial,” and for wind, we say “aeolian.” In contrast, the driving force for mass movement is simply gravity. However, water can sometimes play a role, making material flow farther and more dangerously, such as in debris flows or hyper-concentrated flows, which we’ll discuss later. When you hear about landslides in news reports, the term is often used as a catch-all for various types of mass movement. Even geologists sometimes use it that way, but there are many different types of landslides. Geologists classify them based on three parameters: the type of material involved, the type of motion, and the rate of motion. In this lecture, we’ll focus on the type of material and motion, giving specific names to various types of landslides. The driving force behind any landslide is gravity. To understand this, we can visualize the forces involved with a block diagram, splitting gravity into components. This involves some physics, but it’s important for understanding landslides. Let’s imagine a textbook and a wallet. When the wallet is on a flat surface, gravity pulls straight downward. There’s no component pulling the wallet downhill. But as you tilt the slope, a portion of gravity starts pulling the wallet downhill while another component pushes it into the slope, creating frictional resistance. As the slope angle increases, the downhill force grows stronger until the frictional resistance is overcome, and the wallet slides off. This balance between frictional strength and gravitational pull is crucial in understanding landslides. The critical angle at which material begins to slide is called the "angle of repose." Many natural slopes, especially in mountainous regions, are at or near this angle. Factors such as weathering, water infiltration, or human activities like road construction can disturb this balance, increasing stress on the slope and triggering landslides. Geologists categorize landslides based on motion types, including falls, slides, and flows. Falls occur when material, like bedrock, detaches and falls freely, often from a steep slope or cliff. Slides involve material moving as a coherent block, which can be rotational (curved failure surface) or translational (flat failure surface). Flows, on the other hand, involve chaotic, fluid-like movement of unconsolidated material, often enhanced by water. Debris flows are a fascinating type of mass movement involving a mixture of water, mud, and boulders flowing like a river. These can be incredibly dangerous, carrying massive boulders and causing extensive damage. Mudflows, a subset of flows, consist of finer-grained materials like silt and clay. Both debris flows and mudflows are often triggered by heavy rains, volcanic activity, or events like wildfires, which destabilize slopes by removing vegetation and increasing runoff. Avalanches are another dramatic form of mass movement, often involving dry material like snow or rock. Snow avalanches can reach speeds of 100-150 miles per hour, making them highly destructive. Similarly, rock avalanches involve large volumes of rock moving at high speeds, creating a dust cloud as they descend. Subsidence, a different type of mass movement, occurs when the ground surface collapses due to the removal of support below. This can result from natural processes like water erosion or human activities like groundwater pumping. Sinkholes are a common example of subsidence, often causing sudden and dramatic ground collapses. Lahars, or volcanic mudflows, are debris flows associated with volcanic activity. They can occur during eruptions or after heavy rains, carrying volcanic material down slopes and posing significant hazards to nearby communities. To sum up, landslides happen when the stress on a slope exceeds its strength, causing material to move downhill under gravity. They can be categorized by the type of material and motion involved. Understanding these processes helps us mitigate the risks associated with mass movements. I hope you enjoyed this lecture and find the other course activities on mass movement engaging! Ice Ages & Climate Cycles - YouTube https://www.youtube.com/watch?v=yNiMhjPHPu0 Transcript: (00:02) As we try to unravel Earths history we look for signs in the landscape that provide indications of former episodes of extreme climates. In North America we recognize evidence of a recent ice age and wonder if it has ended or if we are just in a brief warm interlude before another cold interval. We have two learning objectives for this lesson. (00:21) First to discuss the characteristics of ice ages and second to consider how the changing extent of glaciers and ice sheets is influenced by other components of the Earth system. We can identify several ice ages during the last billion years of Earths history. During these times thick glaciers and ice sheets covered large regions of Earth. (00:40) Extensive glacial deposits provide evidence of massive ice sheets that may have extended almost to the equator near the end of the Proterozoic era creating a condition known as Snowball Earth. Ice ages in the first half of the Phanerozoic era indicate times of cooler temperatures and lower greenhouse gas concentrations The most recent ice age, the Pliocene-Quaternary, began less than 3 million years ago and many scientist interpret data from this event to suggest that we are technically still in this ice age. (01:11) During its maximum extent, a sheet of ice a couple of miles thick would have advanced southward out of Canada before retreating again as climate warmed. So why do we get ice ages? Ice ages last for millions of years and are generally related to the relative position of continents and oceans. As you might expect locating continents over a Pole allows ice to build up and may result in an ice age. (01:36) This was the case for the events of the Karoo ice age when several pulses of glaciation occurred over a span of about 100 million years in the Paleozoic Era. However, 3 million years ago the distribution of continents was not much different than today. With one significant exception, water was flowing freely between the Atlantic and Pacific Oceans through a narrow gap that separated North and South America. (02:01) That gap soon closed and circulation patterns in the Atlantic Ocean changed leading to more humid air carried further north and resulting in an increase in precipitation and the development of ice sheets in northern latitudes. Contrary to what many people think, ice ages are not continuous times of extremely low temperature. (02:21) For example, examine this graph to see how temperature varied over 450,000 years This includes the most recent part of the Pliocene Quaternary ice age As you can see an ice age is actually characterized by a series of shorter climate cycles composed of alternating pulses of warmer and colder temperatures. (02:41) We can observe a series of longer cold intervals known as glacials that are interrupted by shorter warm intervals known as interglacials. These alternating cold and warm intervals reflect the advance and retreat of glaciers. The interglacials last for 10,000 to 20,000 years. We may actually be in an interglacial now. Or maybe the ice age has ended. (03:02) We'll just have to wait about 10,000 years to find out. If you look more closely at the graph you can see that even within cold glacials there are significant fluctuations of temperature resulting in colder or warmer intervals. All of these changes can be explained by small changes in the shape of the Earth orbit and/or the inclination of Earth's axis. (03:26) Temperatures in the polar regions become colder if Earth's orbit takes it farther from the sun during winter. and if there is an increase in the tilt of Earths axis. Over the course of tens of thousands of years these types of changes have the potential to drastically change Earth's climate. When they all align in just the right way they can lead to substantial warming or cooling trends to generate glacials and interglacial cycles as well as shorter more frequent cycles within these intervals. (03:52) Okay, so now we know that several long lasting ice ages have been triggered in Earth's history due to changes in the relative positions of continents and oceans and that climate cycles through warm and cold intervals during these events. but what causes an ice age to be sustained or to end. We'll consider the factors to help sustain an ice age to be positive feedbacks and processes that lead to the end of an ice age as negative feedbacks. (04:18) Perhaps the most significant positive feedback arises from the ice itself. Ice and snow make very reflective surfaces, the term albedo is used to describe the reflectivity of a surface. Bright, shiny or light colored surfaces have high albedo values and will reflect solar radiation. Reflection results in less solar energy being absorbed at the Earths surface and produces a cooling effect. (04:42) In contrast, dark surfaces like forests or oceans have low albedos and will absorb solar radiation and become warmer. Positive feedbacks in the climate system would result in larger ice sheets. Ice sheets reflect solar energy causing less to be absorbed and leading to a decrease in temperatures, and thus sustaining the growth of the ice sheets and prolonging the ice age. (05:02) Further, the growth of ice sheets would diminish the area of the globe covered in by dark ocean waters and forests. Further reducing the solar energy capable of being absorbed. In contrast negative feedbacks represent processes that result in an increase in temperature that would encourage melting of the ice sheets and the expansion of the oceans and forests. (05:23) This might result from gradual changes in the distribution of continents and oceans or from an increase in atmospheric carbon dioxide concentrations. Carbon dioxide and other greenhouse gases would trap heat close to Earth's surface, accelerating the collapse of ice sheets. Such an influx of gases would result from volcanic eruptions or from the decrease in photosynthetic activity due to cooler temperatures. (05:47) So for today we had two learning objectives How confident are you that you could successfully complete both these tasks?