The Critical Zone



A remarkable aspect of Earth's surface is the seemingly infinite variety of landforms. However, some landforms possess certain characteristics that differentiate them from other landforms, a fact that is fundamental to geomorphology, the field-oriented study of landforms at the interface between geology and many other disciplines working to understand surface processes. The applications of geomorphic knowledge can range from engineering projects dealing with the physical properties of landforms to geological studies of the record of past climate change recorded by landforms. It is this overall lack of rigid philosophical boundaries that may be geomorphology's greatest attribute—interdisciplinarity (Ritter, D. et al., 2002, Process Geomorphology, 4th edition, p. 1–2).

Diversity in the Critical Zone is displayed by the distribution of soils across landforms, reflecting variable chemical and mechanical weathering processes as well as physical erosion and chemical denudation. These processes in turn control the internal structure of the Critical Zone, the feed-through reactor of Anderson et al. (2007), through which changes in surface area, flow paths, and material residence time impact element and nutrient weathering fluxes.


In succeeding sections 3 through 7 we will explore five classes of geomorphic environments and the processes that occur with them. Before we launch into this more detailed study, I want you to more fully understand basic concepts of topography, including the influence of slope orientation or aspect on pedogenesis, by completing the following activity.



For this assignment, you will need to record your work on a word processing document. Your work must be submitted in Word (.doc) or PDF (.pdf) format so I can open it. In addition, documents must be double-spaced and typed in 12 point Times Roman font.
  1. Read the following book selection, which is available online through Library Reserves:
    • Chapter 9 in Birkeland, P. W. (1999). Soils and Geomorphology (3rd ed.). New York: Oxford University Press.
      You should leave the reading with a firm grasp of the soil catena concept. As you progress through the reading, consider the effects of topography on your soil study site. Also think how the feed-through reactor and chemical weathering fluxes might operate in your soil study site and how it might vary between nearby environments.
  2. Record your thoughts (from step 1) in the form of a one-page paper.
  3. Save your paper as either a Microsoft Word or PDF file in the following format:

L9_catena _AccessAccountID_LastName.doc (or .pdf).

For example, student Elvis Aaron Presley's file would be named "L9_catena _eap1_presley.doc"—this naming convention is important, as it will help me make sure I match each submission up with the right student!

Submitting your work

Upload your paper to the "Lesson 9 - Catena" dropbox in Canvas (see the Modules tab) by the due date indicated on our Canvas calendar.

Grading criteria

You will be graded on the quality of your writing. You should not simply write responses to the questions and submit them to me. Instead plan on writing a short stand-alone paragraph (or page or whatever you decide is necessary considering any constraints I might have placed on you) so that anyone can read what you've written and understand it. You should strive to be specific and complete in responding to the questions. Your answers should be analytic, thoughtful and insightful, and should provide insightful connection between ideas. The writing should be tight and crisp with varied sentence structure and a serious, professional tone.