This photo shows landslide debris atop Buckskin Glacier in...

This photo shows landslide debris atop Buckskin Glacier in Denali National Park in the rugged Alaska Range. The glacier feeds a river that flows into Cook Inlet, just west of the city of Anchorage. Cook Inlet is an arm of the North Pacific. a. Based on what you learned about sorting of sediment in Chapter 7 (Figure 7.7 , page 190 ), would you expect the material deposited by the landslide to be well sorted? Why or why not? b. Also referring to Chapter 7 and Figure 7.7 , would you expect the particles in the landslide debris to be rounded or angular? Explain. c. These mountains are clearly being sculpted by glaciers. However, other processes also have important roles. Identify these processes and briefly describe the role that each plays in the evolution of this mountainous landscape.

This photo shows landslide debris atop Buckskin Glacier in Denali National Park in the rugged Alaska Range. The glacier feeds a river that flows into Cook Inlet, just west of the city of Anchorage. Cook Inlet is an arm of the North Pacific.
a. Based on what you learned about sorting of sediment in Chapter 7 (Figure 7.7 , page 190 ), would you expect the material deposited by the landslide to be well sorted? Why or why not?
b. Also referring to Chapter 7 and Figure 7.7 , would you expect the particles in the landslide debris to be rounded or angular? Explain.
c. These mountains are clearly being sculpted by glaciers. However, other processes also have important roles. Identify these processes and briefly describe the role that each plays in the evolution of this mountainous landscape.

Key Concepts

Sediment Sorting

Sediment sorting refers to the arrangement of grains by size within a deposit. Processes such as water or wind transport typically result in well sorted sediments because particles are separated based on density and size. In contrast, deposits from rapid events like landslides are often poorly sorted since they include a wide range of particle sizes deposited together.

Particle Shape and Rounding

Particle shape is indicative of the history of transport and abrasion. In environments where particles are subjected to prolonged transportation and collisions, such as in fluvial systems, they tend to become rounded. However, deposits from landslides, which involve abrupt movement with little abrasion, tend to preserve more angular, unrounded particles.

Glacial Processes

Glacial processes involve the movement of large ice masses that erode, transport, and deposit sediments, significantly shaping mountain landscapes. As glaciers advance and retreat, they sculpt the terrain, forming features such as moraines, U-shaped valleys, and cirques through the mechanical erosion of bedrock.

Other Erosional and Tectonic Processes in Mountain Landscapes

Mountain landscapes are also significantly influenced by additional processes such as weathering, fluvial erosion, and tectonic uplift. Weathering breaks down rock through chemical, physical, and biological means, while fluvial erosion carried out by rivers and streams transports and further shapes sediment deposits. Tectonic uplift continuously raises the mountain ranges, providing the energy for ongoing erosion and landscape evolution.

Transcript

00:01 In this problem, we're told that in analyzing certain geological features, it's often appropriate to assume that the pressure at some horizontal level of compensation deep inside the earth is the same over a large region and is equal to the pressure due to the gravitational force on the underlying material.

00:17 So the pressure at the level of compensation is given by the fluid pressure formula, but one of the problems is that we have to, whenever there's a mountain or some large perturbanes on top of the continent, here, we have to have a compensation route here of continent sticking down into the mantle such that the pressures in the mantle are equalized.

00:42 So we're told that we have a mountain here that's at a height that has a height of six kilometers.

00:50 The continent has a thickness of 32 kilometers.

00:56 We're told that the density of the continental rock is two point.

01:00 Grams or centimeter cube, which is 2 ,900 kilogram per meter cube.

01:05 And we're told that the density of the mantle is 3 .3 grams per centimeter cubed, which is 3 ,300 kilograms per meter cube.

01:14 And we want to find out if we're given this mountain height and the continent depth thickness, what d needs to be, how deep this root needs to be, so that these pressures are equal down here.

01:26 So we can look at the pressure at a, which is the pressure not under the mountain.

01:34 So we have the density of the continent times g times the thickness of the continent, and then plus the density of the mantle times g times the depth down to the mantle, which is capital d plus little d, which is our distance from the t, the end of the root to where we're measuring pressure at in the mantle.

02:01 And we're told that that will cancel out and we see that in fact it does.

02:04 Pressure at b under the mountain is row of the continental rock, g.

02:12 And so then the depth of continental rock we're down under is h plus t plus d...

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