ENVIRONMENTAL GEOLOGY - GEOL 406/506

Module 2, Part 1 - Earth Material and Earth Cycles

Part 1 - Overview of Processes

by Kristin Fletcher and M. K. V. Hodges

Reading:  Chapters 2 and 3 in textbook (Keller, 2000)

Review Tables 1.1 and 1.2 in the text

Review of topics covered in this module in PDF format or in a powerpoint presentation.

Barrier Island Complex . . .U. S. Fish and Wildlife Service photo

INTRODUCTION - Part 1 Overview of Processes

Now that you understand the philosophy and concepts which underlie environmental geology, we will focus on geologic materials and processes. This module spotlights the geologic cycle, rocks and their characteristics, surficial processes, soil characteristics, and the effects of land use. Your instructor assumes you have completed an introductory geology course and have a basic understanding of the topic. If you haven’t, please study this module carefully because it lays the foundation for all subsequent modules.

Part 1 of the Earth Materials and Processes Module begins with the "big picture." It examines the geologic cycle in which earth materials are transformed and reworked. Over time this dynamic recycling process has fashioned all the diverse climates, landforms, and living things that exist on Earth.

Next we’ll study the three rock families. This link will take you to our planetary geology module on the rock cycle: Igneous, sedimentary and metamorphic rocks. Knowledge of rock properties, such as a compressive strength and response to stress and strain, are covered next and are essential to evaluating natural hazards. A look at how earth materials are altered and transported by ice and wind will conclude this section.

Part 2 of the module focuses on soils--how they are classified, their texture and structure, how liquids move through them, and their engineering properties. The module concludes with the effects of land use activities on soil which results in erosion, pollution, and desertification.

THE GEOLOGIC CYCLE

The geologic cycle is a collective term used to describe the complex interactions between the component sub-cycles of tectonic, hydrologic, rock, and the biological cycling of elements known as the biogeochemical cycle. These various subcycles influence each other and may produce natural hazards and processes important to environmental geology such as landslides, earthquakes, volcanic activity, flooding, groundwater flow, and weather.

Diagram courtesy of the USGS

Plate tectonics is the name we give to the process that directly or indirectly creates most of the landforms we see around us. Tectonic plates are large pieces of the earth's lithosphere. They move slowly along the surface, powered by convective currents deep within the Earth. The average rate of tectonic movement varies from 2 to 15 cm/yr, about as fast as your fingernails grow! Visit this USGS website to learn more about plate tectonics.

The Rock Cycle

The rock cycle is influenced by all the other geologic subcycles. For example, tectonic processes provide the pressure and heat necessary to recrystalize some or all of the minerals in a rock and transform it from one rock type to another. Visit the following module in Planetary Geology for Teachers to better understand how these areas of important mineral resources were formed.



Assignment 1:

Visit the following websites and learn about the different tectonic regimes associated with Earth's internal processes. Where do volcanoes and earthquakes occur, and what types of volcanoes and earthquakes are associated with each tectonic regime?

* Volcanoes - This is Volcano World, a great site to begin studying volcanoes, located at the University of North Dakota.

* Earthquakes - U.S. Geological Survey Earthquake website. This site is a good place to begin learning how earthquakes work. Think about where earthquakes occur and how their occurence relates to plate boundaries.



Many people live near plate boundaries. How does this proximity to the plate boundaries affect them?

THE HYDROLOGIC CYCLE - (AKA the Water Cycle)

Click on the diagram to go the Global Energy and Water Cycle Experiment Home Page (The site this diagram came from).



Assignment 2 - - Answer questions a and b below.

The hydrologic cycle describes the movement of water between the mediums of atmosphere, earth, and ocean and back again. In the process, water erodes the land, transports elements as sediment or in solution, and provides essential water resources for humans. Only 0.3 % of the total water in the cycle available for human use.

a. Fresh water makes up what proportion of total water on earth?

b. Approximately what percent of water worldwide is considered polluted?

The Biogeochemical Cycle

The biogeochemical cycle traces the movement of an element, like carbon, in the air, water, on and in the land, and as used by living organisms. This issue is of particular inportance today because large amounts of carbon dioxide are produced by the burning of fossil fuels. Many scientists are concerned that this trapped carbon dioxide may heat the earth’s surface in a process known as the "greenhouse effect."

Assignment 3:

Visit one of the web sites below to familiarize yourself with the "greenhouse effect," then answer the following questions in a few sentences:

• How much carbon dioxide enters the Earth’s atmosphere each day?

• What is carbon dioxide’s residence time in the atmosphere?

• Where does the carbon "go" when its residence time in the atmosphere is over? (hint: check out the carbon cycle)

http://www.windows.umich.edu/earth/interior/greenhouse_effect.html Green house page from the Universityof Michigan

http://www.epa.gov/globalwarming/ EPA Global Warming page

http://gcmd.gsfc.nasa.gov/Resources/FAQs/glob_warmfaq.html NASA FAQs on Global Warming

http://www.ems.psu.edu/~fraser/Bad/BadGreenhouse.html This page by a Penn State scientist presents an interesting discussion of science and the way science is reported in the news, with links to other similar discussions, and a thoughtful discussion of the Greenhouse Effect.

http://www.pbs.org/wgbh/nova/ice/chill.html NOVA online with some intriguing thoughts about the causes of climate change and the relationship between climate change and plate tectonics.



PHYSICAL PROPERTIES OF ROCKS

Environmental scientists must be able to predict the reliable strength of earth materials for land use planning and natural hazard prediction. They determine rock strength by examining a rock’s texture and structure and testing its response to stress before rupturing. A safety factor (SF) is assigned, based on how a rock is expected to respond under compression, shearing, and tensile stresses.

The SF establishes engineering parameters, an upper limit on how much stress a rock can be subjected to before failure. It is important to remember rocks are not homogeneous nor are their properties similar in all directions, so labratory tests on small samples are not the same as field conditions where large inhomogeneities may exist.

Assignments 4:

List or sketch the three types of stress, what physical earth processes might cause each, and what strain would result. Then, write a short paragraph describing the differences in rock strength between a ductile and a brittle substance using the following terms:

* Elastic (brittle) deformation

* Plastic (ductile) deformation

* Proportional Elastic Limit

* Rupture Strength

* Ultimate Strength

A rock’s strength before rupturing is highly variable and depends on many factors such as rock type, texture, chemical composition, internal structures and the presence or absence of fliuds. Furthermore, most rocks are already fractured by joints and faults. Fractured rocks are only as strong as whatever is holding the rock together-gravity or friction, for instance.

Know the basic rock families, how they formed, and the comparative strength of their most common rock types. Note rocks often fracture along one or more planes of weakness, for example, along bedding planes in sedimentary rocks or along foliation planes in metamorphic rocks. The orientation of planes of weakness is very important, too. Why?

Note that some common rocks, shales for example, may share the same name but exhibit radically different engineering properties depending on their deposition as well as lithification processes. Compaction shales are weak and can slide along bedding planes, slake (soften into mud when wet), and swell under certain conditions. However, many cemented shales, depending on the cementing material, can be very strong and suitable for most engineering enterprises. Study the following diagrams carefully.

Familiarize yourself with the following graphs of natural substance behavior. Click here for more information.

Elastic Deformation

Ductile Deformation

Permanent Strain

SURFICIAL PROCESSES

Environmental scientists are not only interested in how subsurface tectonic processes of heat and pressure influence rocks, but also in the effects of surficial processes like ice and wind. Glaciers, for example, once covered about 30% of the Earth’s surface and left their complex signature in moraines, outwash plains, and till. Permafrost, permanently frozen ground, is a fragile combination of water and soil found in the upper latitudes of Canada, Alaska, Europe, and Asia. Both require careful examination before building structures such as highways and dams.

Sand dunes and loess, a silty soil, are the two most common products of wind deposition, covering thousands of square miles in the United States. Sand dunes, unless stabilized by vegetation or human constraint, tend to continue their downwind migration. Loess, on the other hand, is subject to hydrocompaction and may settle or crack unexpectedly if not properly compacted. Both can be highly troublesome unless engineered properly.

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Terms for Understanding:

hydrocompaction geologic cycle tectonic cycle rock cycle hydrologic cycle biogeochemical cycle

greenhouse effect rock strength reliable strength safety factor stress and strain permafrost

ductile & brittle substances elastic and plastic deformation proportional elastic limit ultimate strength rupture strength texture

Link to html glossary for this class

Link to pdf glossary for this class

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Assignments:

Email a copy of assignments 1 - 4 to the instructor at hughscot@isu.edu. Be sure to keep a copy in your files.

Additional web sites of interest:

	Hydrologic Cycle - http://www.und.nodak.edu/instruct/eng/fkarner/pages/cycle.htm
	The Hydrologic Cycle from NRC http://grads.iges.org/nncc/hydro.html
	National Climate Data Center: http://lwf.ncdc.noaa.gov/oa/ncdc.html
	Goddard Institute for Space Studies http://www.giss.nasa.gov/
	Energy Information Administration/ Emissions of Greenhouse Gases in the United States 1995. An exhaustive summary, packed full of data which might be useful to some one writing a term paper. http://eiainfo.eia.doe.gov/oiaf/1605/gg96rpt/chap1.html
	USGS - Global Environmental Change and the Carbon Cycle http://geochange.er.usgs.gov/pub/carbon/fs97137/

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End of Module # 2 - part 1

Did you email your assignments? hughscot@isu.edu

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