The Critical Zone

Lesson 9 Introduction


In the last lesson, you were introduced to the concept of the Critical Zone as a feed-through reactor (Anderson et al., 2007). As we move forward in this unit, I first want you to consider the relationship between the feed-through reactor and isostasy. Imagine a mountainous setting in which active erosion constantly removes weathered material from the summits: the unloading of weathered material allows the underlying crust to readjust by uplift, thereby physically raising unweathered rock rapidly into the feed-through reactor. Eventually, the landscape may mature to one with low topography and little relief as the deep crustal root has been exposed, weathered, and brought toward isostatic equilibrium with the underlying mantle. Thick soil profiles develop and blanket underlying unweathered rock, slowing the rate at which the unweathered rock is processed through the reactor. Furthermore, recall from Lesson 2 (reading Brady and Weil, pp. 41–2 and 61–2) that topography is the configuration of the land surface described in terms of elevation, slope, and landscape position differences, and that topography can hasten or retard the effects of climate on parent material-weathering by creating a balance between erosion and pedogenesis.

Because topography often reflects the distribution of different parent materials in many landscapes, detailed soil maps can be useful for interpreting geology, and geological maps can in places be made directly from soil maps [Birkeland, P. W. (1999). Soils and Geomorphology (3rd ed.). New York: Oxford University Press, p. 31]. Mappable soil bodies typically display patterns of distribution based on underlying bedrock and landforms—to fully understand soils one must make an in-depth assessment of geomorphic settings (Birkeland, p. 49, p. 1).

Having considered the variables associated with bedrock type, the rock cycle, tectonic setting, weathering and erosion in the last lesson, now we will explore geomorphic environments and the processes that can move and shape them to learn about the links between landforms, soils, and the Critical Zone. I'll remind you here, as I did in Lesson 2, to consider the outstanding question in Critical Zone science learned in a Lesson 1 reading (Brantley et al., p. 11): Can a unified approach be developed to characterize environmental conditions and mechanisms that produce different soil types?

What will we learn about in Lesson 9?

  • Geomorphology and the relationship between topography and soil formation
  • Coastal processes and landforms
  • Karst processes and landforms
  • Glacial and periglacial processes and landforms
  • Wind processes and landforms
  • Fluvial processes and landforms
  • Aerial photographic analysis of landforms

Learning Objectives

By the end of this lesson you should be able to:

  • Discuss the notion of the Critical Zone as a feed-through reactor
  • Describe a soil catena and the influence of slope and aspect on pedogenesis
  • Define fluvial, eolian, periglacial and karst
  • Describe and identify some features and processes characteristic of five generalized geomorphic environments
  • Find remotely sensed imagery, specifically aerial photographs, for your study site

What is due for Lesson 9?

Lesson 9 will take us one week to complete. As you work your way through these online materials for Lesson 9, you will encounter additional reading assignments and hands-on exercises and activities. The chart below provides an overview of the requirements for Lesson 9. For assignment details, refer to the lesson page noted.

Please refer to the Calendar in Canvas for specific time frames and due dates.

Lesson 9 Activities
Report (1 page) on topography and feed-through reactor at your study site page 2 Post to the Lesson 9 - Catena dropbox in Canvas

Respond to question on aerial photo availability in your state

Report (1 page) on aerial photo analysis

page 8

Email directly to Tim

Post to the Lesson 9 - Aerial Photo dropbox in Canvas


If you have any questions, please post them to our Questions? discussion forum (not e-mail), located under the Discussions tab in Canvas. I will check that discussion forum daily to respond. While you are there, feel free to post your own responses if you, too, are able to help out a classmate.