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