Introduction to Geography
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Transcript Introduction to Geography
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