This document provides an overview of key concepts in geomorphology. It defines geomorphology as the study of landforms and discusses how landforms are shaped by tectonic and hydrologic processes. Early theories that invoked supernatural causes are contrasted with modern theories of uniformitarianism and plate tectonics. The roles of various controlling factors - including geomorphic agents, surficial materials, tectonic setting, and climate - are examined. Different types of crustal features like continents, mountain belts, shields, and continental shelves are also introduced.
2. The word “geomorphology" comes from the Greek
roots "geo,“ “morph,” and “logos,” meaning
“earth,” “form,” and “study,” respectively.
Therefore, geomorphology is literally “the study of
earth forms.”
Geomorphologists are concerned primarily with
earth’s surficial features, including their origin,
history, composition, and impact on human
activity.
Geomorphology concentrates primarily on
Quaternary (Pleistocene and Holocene) features.
Earth’s landforms reflect the local and regional
balance between hydrologic and tectonic
processes.
What is Geomorphology?
Photo by NASA
3. Supernatural Intervention
• Volcanoes and earthquakes are caused by angry gods and/or devils.
• Fossils placed by the devil to confuse man.
Throughout most of
human history, natural
phenomena have been
interpreted through
myths and legends to be
the result of supernatural
intervention.
4. Creationism is the theory that all earth’s features, from grains of sand
to mountain ranges, were designed and created individually by God.
Creationism
5. Photo by W. W. Little
Catastrophism vs.
Uniformitarianism
Early ideas considered geological features, such as
mountain ranges, to have been created through sudden,
catastrophic, events.
Uniformitarianism is the idea that the same physical,
chemical, and biological processes operating on and in
the earth today were also active in the past and that,
therefore, all geologic phenomena can be explained as
natural occurrences.
6. Scientists make observations of an event or an object and then try to explain those
observations by organizing them into a logical system. As rock bodies can cover extensive
areas and represent vast periods of time, much of geological research cannot be done as
controlled experiments in a formal laboratory setting. In these situations, we rely on the
assumption that physical, chemical and biological laws are constant. That is, the processes
operating today are the same as those that operated in the past. For instance, since water
flows down hill today, it must have done so in the past. Therefore, if we identify a body of
rocks that exhibits characteristics similar to those found in a modern geological
environment, we assume that it must have formed in a similar manner.
Uniformitarianism
Ancient river channels
Modern river channels
Photos by W. W. LittlePhotographer unknown
7. • Both sedimentary and igneous rocks were precipitated in a global
sea. Erosion was caused by the “rush” of water as the sea receded.
• No explanation as to the fate of the missing sea water.
Neptunism
Abraham Gottlob Werner
8. • The ocean floor and continents are both ancient and are fixed in
their positions.
• Mountain ranges formed through crustal contraction during gradual
cooling of a molten planetary surface. Similar to the wrinkling of
dried fruit.
• Crustal folding and sea-level changes (uplift/subsidence) are due to
cooling and contraction of the earth's interior.
Shrinking Earth Theory
9. Virtually everything we see on the earth's surface is the result of the
interaction between two dynamic systems - tectonics and hydrology.
Dynamic Systems
From Tarbuck and Lutgens
10. Plate tectonics is the process by which rock material is moved from
within the earth to its surface and, in some cases, back to its interior and
by which the lithosphere is broken into a series of plates that move with
respect to one another.
12. • Driven by the earth's internal heat, which is generated by the radioactive decay of K, U, Th, and
other elements; by friction as material moves through the earth, and from residual heat related to
planetary accretion.
• Responsible for earthquakes, volcanic activity, mountain formation, and continental drift
• Builds things up
• Primary processes include mantle convection and isostacy
Tectonic System
Unknown source
13. Controlling Factors for
Geomorphology
Tectonic Factors
• Structural style (normal faulting, thrust faulting, folding, vertical uplift)
• Plate position (active margin, passive margin, somewhere in between)
Hydrologic Factors
• Climate (temperature, humidity, atmospheric and oceanic circulation patterns)
• Transporting medium (flowing water, ice, wind, waves, tides)
Prior Geologic History
• Nature of surficial materials
• Inherited structures
Geomorphology reflects the local and regional balance between
tectonic and hydrologic forces.
14. Controlling Factors
Geomorphic Agents and Processes: Affect how rocks and sediment
are eroded and transported.
Surficial Materials: Rocks and sediment of different types are
located at the earth’s surface.
Tectonic Setting: Determines what materials are exposed at the
earth’s surface and the manner in which they are distributed.
Climate: Determines what geologic agents are available to interact
with exposed rock materials and influences the rate of physical and
chemical reactions.
15. Controlling Factors
Geomorphic Agents and Processes: Affect how rocks and sediment
are eroded and transported.
Surficial Materials: Rocks and sediment of different types are
located at the earth’s surface.
Tectonic Setting: Determines what materials are exposed at the
earth’s surface and the manner in which they are distributed.
Climate: Determines what geologic agents are available to interact
with exposed rock materials and influences the rate of physical and
chemical reactions.
18. There are two major crustal components, continental masses and ocean
basins. They differ in elevation, rock type, density, chemical
composition, age, and history.
Crustal
Features
19. • Relatively low density rocks derived from felsic and intermediate
sources.
• Include the oldest rocks on earth (up to 4.0 Ga).
• Divided into 4 major components; shields, stable platforms, mountain
belts, and continental shelves.
Continents
Mountain Belt
Shield
Stable
Platform
Continental
Shelf
23. From Tarbuck and Lutgens
• Typically found along continental margins
• Linear belts of folded sedimentary layers overlying intrusive
igneous and metamorphic rocks
• Highly deformed by horizontal and vertical forces
• Characterized by internal zig-zag pattern
• E.g. Rockies and Appalachians
Folded Mountain Belts
35. • Regional surface of low relief with gentle warping
(resembles the shape of a Greco-Roman shield).
• Metamorphic and intrusive igneous rocks formed deep
within the earth and later elevated to the surface through
isostacy as overlying material was eroded.
• E.g. Canadian shield
Shields
42. From Hamblin & Christiansen (2001)
• Horizontal and slightly deformed sedimentary layers overlying
the shields.
• Little deformation or vertical movement over hundreds of
millions of years.
Can have broad domes and basins
• E.g. U.S. Midwest between the Rockies and the Appalachians.
Stable Platforms
67. Continental shelf
• Submerged, flat continental area
• Very low seaward gradient
• Thick sediment cover obscures complex underlying fault structures.
Continental slope
• Edge of continental shelf to sea floor.
• Steeper than shelf, but still relatively flat.
• The base of the slope is known as the continental rise.
• Can include thick, fan-shaped deposits formed by submarine "avalanches."
Continental Shelves
From Tarbuck and Lutgens
Continental Shelves and
slopes are considered to
be parts of continents but
form transition zones with
ocean basins.
Editor's Notes
In this first lesson, you will be introduced to the processes that govern the development of earth’s physical features. You will learn that there are two fundamental systems responsible for virtually everything we see at the earth’s surface. These are the tectonic and hydrologic systems. The tectonic system is driven by the earth’s internal heat and tends to build things up, producing angular features. Mountain ranges, earthquakes, volcanoes, island chains, and the break up and drifting of continents are all products of the tectonic system. The hydrologic system receives its energy from the Sun and wears things down, smoothing out the angular features produced by tectonics. Rivers, lakes, sand dunes, glaciers, and beaches are all the result of hydrologic processes. What we see at any one spot on the earth’s surface is the result of the local balance of these two opposing systems. Where the tectonic system dominates, high mountains are formed and shorelines are irregular. The west coasts of North and South America, the island chains of the Pacific Ocean, and the Himalayan Mountain Range are areas dominated by tectonic processes. Areas influenced primarily by hydrologic processes tend to be flatter with relatively smooth coast lines, such as the great plains and Gulf coast of the United States.