Introduction to Geography
People, Places, and Environment, 4e
Edward F. Bergman
William H. Renwick
Chapter 3
Landforms: The Dynamic Earth
Victoria Alapo, Instructor
Geog 1010
Geomorphology


Study of landforms and processes that
create them
Lithosphere comprises of:


Rocks and soil
Surface landforms

Plains, hills, valleys, depressions
Landform Processes

Endogenic

Internal forces beneath or at Earth’s
surface



Mountain building
Earthquakes
Exogenic

External forces

Erosion, water, wind, chemical
Plate Tectonics

Fixed Earth Theory


Plate Tectonics Theory



States that continents and oceans have
always been fixed in place
Proposed by Alfred Wegener, 1900s
Became popular in the 1960s
Pangaea Hypothesis

First a supercontinent, and the tectonic
plates moved (see next slide – plate
boundaries)
Plate Boundaries
Earthquakes

Focus


Epicenter



Surface directly above focus
See next slide – epicenters
Seismic waves


Place of actual movement
Recordable vibrations
Seismograph


Recording device for
seismic waves
Richter Scale, 1935
Earthquakes
Volcanoes

Magma


Lava


Molten rock underneath the earth
Molten rock reaching Earth’s surface
Volcano

Surface vent for lava
Volcano Types

Shield volcanoes




Sedate
Runny lava
The Hawaiian Islands: Mauna Loa, Hawaii (still
active, but not explosive)
Composite cone volcanoes



Explosive
Pyroclasts – this explosive material includes sticky
lava, hot ash, sulfurous gas, rock bombs, etc – e.g.
Pompei
Krakatau in Indonesia, largest recorded eruption.
Plate Boundaries

Divergent

Plates spreading apart, leading to:



Convergent

Plates push together, leading to:



Seafloor spreading
Rift Valleys in Africa
Mountain building
Volcanic eruptions as dense plates dive below
Transform


Grinding of plates past each other, leading to:
Offset sidewalks

E.g. along the San Andreas Fault, CA
Rock Formation

Igneous



Sedimentary



Cooled molten crustal material (magma)
E.g. Basalt, granite
Sediments laid down in layers and from high pressure
E.g. Sandstone, shale, limestone
Metamorphic


The 2 rocks above can be later compacted again, by
heat & pressure, and so undergo further change
E.g. Marble derived from limestone
Weathering


Process of breaking rock into pieces
The first step in the formation of soil

Mechanical weathering


Process of rocks breaking down by physical force, e.g. tree
roots, freezing & thawing - pot holes. See next slide.
Chemical weathering

Process of breaking down rock by:





Exposure to air and water
Acids released by decaying vegetation
Oxidation (rust due to iron content)
Leaching (nutrients being washed downwards beyond plant
roots)
Decomposition of calcium carbonate
Mechanical


Frost Wedging: the most important type of mechanical weathering;
freeze-thaw repetition. Also responsible for city pot-holes.
Personal home experiment
Fig. 15-7 and 15-8
Movement of Weathered Material

Mass movement could be:


Slow gradual movement occurring near the surface, like soil creep
Or in dramatic movements such as rock slides, landslides and
mudflows
Glaciers

Slow moving “rivers of ice” flowing from colder to warmer
regions. They move only a few feet per year.

They act like conveyor belts, picking up sediment and
dropping it in depositional areas

These glacial sediments are called, Moraines




Terminal moraines – found at the very end of glacier
Lateral moraines – found along the sides
Medial moraines – found in the middle
See next slide
Moraines
Impact of Past Glaciations

Soils & Landforms


Advance and retreat of glaciers leave behind highly
fertile soil and various landforms (see next slide).
Water supply & Transportation routes

Retreating glaciers left sand and gravel deposits
yielding large supplies of ground water

Also, water transport is heavily influenced by
glacial melt water channels left behind by receding
glaciers. E.g. Great Lakes, Hudson Bay, etc. See
pg 117.
U-shaped valleys
& jagged/rugged
landscapes
Coastal Erosion

Longshore currents:

Currents traveling parallel to the shore, caused by repeated
breaking of waves. Capable of carrying enormous amounts of
sediment, and changing the form of beaches.
Coastal Erosion
Effects of longshore currents:
Rate of Landform Change
Environmental Hazards

Environmental processes

Natural


Tornadoes, landslides, earthquakes
Human vulnerability


Rebuilding after natural disaster e.g. Pompeii, Italy;
New Orleans, hurricane areas of Florida, California, etc
Trusting in Seawalls & Levees, instead of living
elsewhere