Page 2
Geomorphology - Surficial Processes and Landscapes*
* I strongly recommend that you study this material 
only after we cover mountain building in lecture, or you 
first look up and read about "isostasy" in your textbook.

Part I - Erosion and Landforms

    The forces of degradation (see below) all in some way aid the process of erosion. Erosion is "the physical removal of sediment by the action of streams, glaciers, waves, wind, and underground water." Therefore, contrary to some definitions, I consider erosion to be distinctly separate from weathering and mass wasting. We have already examined weathering in some detail. We will cover mass wasting a bit later in this lesson.
    I would just like to add that weathering doesn't end on the outcrop. Sediments continue to decay or alter chemically and experience physical abrasion as they move from the outcrop to their final resting place. In fact, this is part of the reason that grain size of sediment decreases downstream in rivers. So erosion stops once a grain is entrained by some type of erosional agent (wind, water, ice, etc.) but weathering does not. In any case, together the geomorphic processes listed below produce the byproducts of the sedimentary rock cycle (sediment, soil, mineral-rich solutions, and sedimentary rocks) as well as landforms.
 
Geomorphogenesis ("land" + "form" + "origin") is controlled in many way by many different factors. I've listed some important processes that: (1) you should definitely think about, (2) we will talk about in future lectures, and (3) I'll ask questions about on tests. Some of these processes operate at the Earth's surface, others work in the subsurface. Most surficial processes (except sediment deposition) degrade the landscape (i.e. wear it down) whereas most internal processes contribute in some way to building up (aggrade) the surface. So in a sense, external forces battle internal forces for control of the appearance of the Earth -- and wouldn't that make a great sci-fi flick? Just imagine the special effects that could be put to work illustrating the diametrically opposed processes battling it out to determine the fate of Earth's surface. OK, enough of that. You get the idea. 
The end result is a landform.

Major influences (aka "controls") on rates of geomorphogenesis
    1. slope
    2. tectonics
    3. bedrock geology
    4. sea level variation
    5. isostatic movements (uplift, subsidence)
    6. climate (including vegetative cover)
If you use a little imagination and a bit of deductive reasoning you can probably figure out, for example, how slope or geology might influence the character of a landscape. However, let's see instead how you do applyinig your powers of reasoning to the following question:
D? What "drives" erosion?
    All processes require energy to operate, so that is what this question is really asking. In class, I probably get one correct answer (there are two types of energy involved) about 40% of the time -- not a good average.
    I often end up pointing out that rain is critical to erosion -- and then I get the correct answer for one of the energy sources -- the sun. Solar energy drives the hydrologic cycle. Without the hydrologic cycle, erosion wouldn't be very effective. As you already know, we would not see much chemical weathering either.
    The second energy source is rarely on the tip of anyone's tongue. However, in grade school you probably (I hope) learned about the different types of energy: mechanical, nuclear, heat (i.e. chemical), kinetic, and potential energy, also known as energy of position. The latter energy type is really just another way to say "gravity" -- which is our other energy source. It should be obvious that gravity causes rain to fall, the wind to blow, rivers to flow, and boulders to roll over the edge of cliffs -- all examples of erosional agents or erosional activity. Need I say more?

D? What do you think is the most common landform? (Hint: consider what "carves out" most hills)

    This is a question that once you hear the correct answer and why it is correct, you shouldn't have any trouble remembering it (I hope.) Most students end up guessing "mountains" (not an especially good guess, i.e. how many mountains are there in all of Tenn.?) or hills (a pretty good answer). But if you try to mentally picture a hill -  and later in lab you will do just that -- you should see a few stream valleys as well. Yes, indeed, stream valleys are the Earth's most common landform because most hills have more than one.

D? Two processes, one internal and one external, can result in an apparent "raising" of the land surface (i.e. an increase in slope length & angle). What are they?

    I've provided you with a list of processes at the top of the page. Can you apply a little critical thinking to this question and intuit the answers? It should be obvious that several of the internal process can effectively raise the land: isostasy, mountain building, deformation -- these can all cause uplift and that raises the land surface. On the other hand, one of the external processes achieves the same result in a very different way. Which one is that, you ask? The answer is: sea level change. When sea level falls (e.g. during an Ice Age), that is akin to raising the land surface. Notice that both of these also appear in my list of major influences on rates of geomorphogenesis. That is no coincidence.

Either one of these causes rivers to have a steeper gradient (vertical drop/linear distance of channel) and therefore to begin more actively downcutting its channel. The Grand Canyon is a great example of a landscape produced by rapid uplift and aggressive downcutting by a stream channel (i.e. the Colorado River).

Now that I've illustrated a couple of the concepts from the processes and products lists at the top of the page, let's move on to other topics. Page 2