introduction to geography people, places, and environment, 4e edward f. bergman william h. renwick...
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Introduction to GeographyPeople, Places, and Environment, 4eEdward F. BergmanWilliam 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 States that continents and oceans have always been fixed in place
Plate Tectonics Theory 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 Place of actual movement
Epicenter Surface directly above focus See next slide – epicenters
Seismic waves Recordable vibrations
Seismograph Recording device for seismic waves Richter Scale, 1935
Earthquakes
Volcanoes
Magma Molten rock underneath the earth
Lava 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:
Seafloor spreading Rift Valleys in Africa
Convergent Plates push together, leading to:
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 Cooled molten crustal material (magma) E.g. Basalt, granite
Sedimentary 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