GEOL101 LAB 11

GEOL101 Dynamics of the Earth – Fall 2023 Name: Lily Razzano Laboratory 11: Geomorphology Section: 1003 Introduction In this lab, we will explore geomorphology, which is the study of how landscapes form and evolve over time. Common landscapes that may be characterized as fluvial (river-driven), aeolian (wind-driven), glacial (glacier-driven), tectonic (earthquake fault-driven), and mass movement (gravity-driven). Geologists study these driving processes to understand, and sometimes predict the behavior of geomorphic processes. This is important for Californians because we have a quite varied landscape from the northwest (forested, many rivers), to the east (dry, snow accumulation in the mountains, and basin and range faulting), to the southwest (transform faults, and variable precipitation), and to the west (coastal wave and tide action, heavy precipitation and river input). In this lab, we will “tour” these landscapes and explore the driving forces that produce them. As with all of geology, the landscape of a given location will evolve over time in response to one or more of these driving forces related to gravity, water, ice, wind, and tectonics. Fluvial (River) Landforms Two general styles of fluvial landforms commonly found in nature are braided rivers and meandering rivers. Braided rivers are rivers that are essentially choked with an abundance of sediment or have a high degree of slope. The river's response to not being able to move the abundant sediment is to break into many, many channels. Braided rivers occur commonly in glacial regions, arid environments (alluvial fan), and deltas (due to a very low river velocity, and therefore, a more limited ability to transport sediment). Due to the abundance of channels in a braided river system, islands are formed between the channels as they wind through their environment. These islands are called braid bars . This generally is a response to abrupt changes in river velocity, which can be driven by seasonal and daily changes to water input to the system, or a response to tectonic events. Figure 1. Braided river system in Alberta, Canada. Photo by Will Buckley Meandering rivers are rivers that “meander” or wander over time across a valley or floodplain. These rivers are different from braided rivers because they are generally confined to a single channel at any given time. The sinuosity of these rivers can form sharp curves as water flows moves quickly along the outer edge of a curve and actively erodes the land forming a steep cut bank . On the inner edge of the curve, water moves relatively slowly and sediments tend to settle out and be deposited as a gently sloping point bar . Point bars and cut banks will migrate laterally over time. In addition, in some cases, a cut bank may cut through the channel wall of the river, finding a shorter path for the river since water will always take the easiest way down slope. On the following page is a diagram illustrating what these forms look like. Please use this as a guide to answer questions regarding fluvial landforms later in the question portion of the lab. Figure 2. Aerial photo of a meandering river system in Alaska. Photo by Will Buckley Figure 3. Diagram of meandering river features. (www.schoolworkhelper.net) Figure 4. Additional diagram of meandering river showing various descriptive features. (www.internetgeography.net)

Aeolian (Wind-driven) Landforms If you have been to the beach, then you are familiar with the transport of sediment by wind because you have seen the dunes that form there. These dunes are created by winds that move grains of sand. The formation of a dune is a direct response of sand grains to the direction of wind, whether it is in constant or changing direction. Lastly, the formation of a dune may depend on whether or not there is vegetation present to provide an anchor around which a dune may form. The beach is not the sole environment where dunes can form. As you may have seen in some movies, if you have not been to the desert, sand dunes may form in a desert environment as well! Below are multiple styles of dunes that geologists’ study, please use the above text and Figure 6 on the next page to help you to answer questions on Aeolian landforms in the lab. Figure 5. Sand Dunes in Death Valley. (Photo by Michael Shainblum) Figure 6. Different types of sand dunes and their relation to wind and sand availability. Glacial landforms Throughout earth’s history, glaciers have had a varied past. They have at times covered the entire earth (snowball earth!), cycled between advancing and retreating or been completely absent from the earth’s surface. Glaciers consist of snow that has turned to ice, also known as firn . When glaciers advance, they grind up the rocks and sediments over which they move. When they retreat, they leave glacial deposits of sediments behind. These glacial deposits leave clues for geologists to study both the past behavior of glaciers and the type of climate that existed in the geologic past. We are currently in a period of glacial decline that is unprecedented in the speed in which it is occurring. 99% of geologic scientists agree that human contributions of carbon dioxide and other greenhouse gasses are a major factor in this current event. In this section, we will examine the landforms that can be observed where glaciers are the agents of geomorphic change. When a glacier moves downhill under the influence of gravity, it carries rocks, boulders, and sediments (the amalgamation of this material is known as glacial till). The glacier deposits glacial till in front of it ( terminal moraine ), along the sides ( lateral moraine ), and sometimes, in the middle of two glaciers that are merging into one from separate valleys ( medial moraine ). When the glacier retreats or melts, these forms are left behind for geologists to observe. As a glacier grinds away at the rock underneath of it, it creates a very distinct shape of valley called a U-shaped Valley . River valleys are different from glacial valleys since they cut valleys with steeper sides, known as V-shaped valleys. During times of melting, subglacial streams flow under the glacier and create stream deposits of cobbles, gravel, and sediment. When the glacier retreats, these deposits are exposed and known as eskers . There are multiple other types of glacial landforms: horns (think the Matterhorn in Switzerland), arêtes (sharp ridges), cirques (like an amphitheater carved out of the side of a mountain), and tarns (glacial lakes from meltwater, that reside in cirques). For these features to have been formed, think of how much ice must have been present to have worn down the underlying bedrock, miles thick in some cases! If you were to find yourself in a situation when crossing a glacial-fed river is necessary, it is important to consider how the glacier contributes to river flow before crossing . When a glacier is the primary source of water for rivers, the volume and velocity of river flows can fluctuate at different times of the day and year. Generally, the volume and velocity would be highest during warmer temperatures when glaciers melt more frequently and would make crossing a river during these times more difficult. Examine the below diagram and use it to answer questions in the question portion of the lab on glacial landforms. Figure 7. Diagram of features associated with alpine glaciation. (www.indiana.edu/~sierra/papers/2012/klapperich.htm)

Lab 11 Questions Question 1. Answer the following questions regarding Figure 1. Notice the ‘islands’ between channels of the braided river. These are called point bars. What are they typically a result of? The point bars are the result of the deposited sediments which are not moved away by the rivers or streams and these streams branch out around the sediments to form point bars. Are braided rivers associated with a high or low amount of sediment? The braided river system is associated with huge amount of sediments. This is the reason why rivers are not able to move such huge amount of sediments either at delta or towards the source in case of glaciers. Braided rivers typically transport and deposit coarse sand and gravel-sized sediment. What does this tell you about the energy of a braided river? Deposition of coarse sand depicts the low energy of the stream and the velocity is less and thus is the very reason why sediments are rather deposited and not moved away by the river. The river is located at the outlet for meltwater from a glacier in Alberta, Canada. Imagine having to cross the river while you’re on a backpacking trip in the summer; however, it must be done when the velocity and volume of the water is low. When would be the best time of the day to cross the river and why? Keep in mind that a glacier largely controls the water load. Crossing the river channel while backpacking and touring would be best feasible when the water volume is low and slow. This is possible when the glaciers would melt less or it would freeze completely and there will not be rainfall. This is best possible during winter and just after the sunrise as the temperature in the early morning is freezing cold. Question 2. Answer the following questions regarding Figure 2 (use Figure 3 to help determine features). What feature does arrow A point to? Point A refers to the erosional part. This point is heavily eroded by the fast velocity of the stream. What direction is arrow A’s feature migrating towards (north, south, east, west)? The direction is towards east, of the feature indicated by arrow A. What feature does arrow B point to? The feature pointed to by arrow B is called an oxbow lake. Oxbow lakes are formed when the meanders formed over the course of time become sharp and very curvy and due to the fast

velocity, the river channel cuts a branch and forms a new course thus separating the old channel and hence oxbow lakes are formed. What feature does arrow C point to? Would this feature be associated with deposition or erosion? C represents the depositional feature of meanders. Here the velocity of river is such that it deposits sediments. Question 3. Answer the following questions regarding Figure 6: Sand dunes are typical features in desert environments. What other environment might sand dunes be found? The sand dunes are generally formed in desert environment but it can also form in coastal environments. In the coastal environment a lots of sand particles are present due to erosion so if it will get sufficient flow then sand dunes can form. Dune formation is dependent on what three main factors? Dune formation is mainly dependent on 3 factors: 1. The amount of sand available 2. Speed and direction of wind 3. Vegetation What can a Barchan dune turn into if the sand supply increases? Barchan dune is a crescent shape dune that is formed when a limited amount of sand is supplied and flow of wind is unidirectional. When the sand supply increases then it will turn into a transverse dune which forms at the right angle to the prevailing wind direction when sand supply is high and wind flow is unidirectional. Question 3. Answer the following questions regarding Figure 7. How can you tell if a valley has been formed by a glacier, as opposed to a river? In contrast to the V-shaped valleys carved by rivers, valley glaciers carve U-shaped valleys.When the climate on Earth cools, glaciers form and start to move downhill.They frequently choose the shortest route and settle in the small, V-shaped valleys that once belonged to rivers.

Earth Flow Speed: Slow Nature of motion: Flow Material type: Unconsolidated material Water/air content: High water content. What are the main factors that contribute to the occurrence of mass movements? Must name them all. Slope angle and steepness Type and structure of the material involved Water content and saturation Vegetation cover and stability Geological and tectonic factors Human activities such as mining, construction, and deforestation. What feature(s) do braided rivers show to indicate braided river flow? Braided rivers typically show a network of multiple interconnected channels that diverge and reunite. The channels are separated by bars or islands of sediment, which can change rapidly in shape and position due to the dynamic flow of water. Question 5. Use Figures 9 and 10 and the text above them to answer the following questions: What are tectonic landforms created by? Structural landforms result from Earth's plate developments at limits: dissimilar (plates isolated), concurrent (plates impact, shaping mountains), and change (plates slide past one another). Structural landforms are geographical elements framed because of surface misshapening processes driven by the development of the World's lithospheric plates. The World's hull is partitioned into a few plates that move comparative with one another, prompting different communications at plate limits. What features do offset streams provide that help to measure the offset of a fault, and how might one use these features to measure the offset?

Stream channel offset distinguishes strike-slip blames and gauge their slip rates. At the point when a strike-slip issue cuts across a stream channel, it can dislodge one side of the channel comparative with the other, bringing about an offset. By estimating the offset and concentrating on its relationship to the issue, geologists can gauge the geological shortcoming slip rates, which are fundamental for grasping seismic risks and structural cycle What feature forms when a depression in the landscape is created from a step-over in the fault? Dejections are depressed landforms, and step-overs move strain between equal flaws; they can be limiting or delivering.