World Geography 3202 Unit 1 Ch. 1: Landform Patterns and Processes
- Planet Earth is dynamic - behaves as if it s a living organism - some changes are rapid enough for us to see and record - exs. Tidal activity, volcanic eruptions, flowing water/glaciers - other changes occur at an almost unnoticeable pace - exs. Mountain building, continental movement, seafloor spreading
STRUCTURES ON EARTH S SURFACE - surface of Earth not flat - consists of humps, bumps, depressions - surface continually being acted upon by: i. internal forces heat/pressure & continental movement ii. external forces volcanoes, ice, waves, wind, water the shape of the Earth s surface is referred to as TOPOGRAPHY
HOW LANDSCAPES CHANGE - 1924 ALFRED WEGENER proposed THEORY OF CONTINENTAL DRIFT - all continents once joined in super continent (PANGAEA) & surrounded by ocean (PANTHALASSA) - ~ 200 million year ago Pangaea split into 2 sections which further segmented into present continents
Continental Drift (cont d) - continents proposed to have drifted to present locations - Wegener s theory dismissed could not explain how drifting occurred - He suggested perhaps due to the centrifugal force resulting from spinning of earth on its axis
Continental Drift (cont d) - since 1930 s, the following evidence has been accumulating lending support to Wegener s theory: i. boundaries of continental shelves fit very closely in some areas ii. rock strata match on different continents iii. climate changes in some areas too drastic to be accounted for by world-wide climate change - ex. Coal deposits in Antarctica
Continental Drift (cont d) iv. iron oxide particles in old rock in Britain aligned 30 to left of magnetic poles of such particles in younger rock v. perhaps greatest support provided by Canadian scientist J. Tuzo Wilson in 1960 s - observed earthquakes/volcanoes often occur in mid-ocean regions - discovered Mid-Ocean Ridges (ex. Mid- Atlantic Ridge)
Continental Drift (cont d) - rock layers along each side of these ridges matched in terms age and magnetic imprint - along theses ridges SEA-FLOOR SPREADING occurs with continents moving apart - this has been verified in past few decades by seismic studies, satellite photography & rock/fossil studies
Continental Drift (cont d) - it has been determined that the Earth s crust is not a singular piece of crustal material - made up of pieces called PLATES - within Earth is energy heat & pressure acting upon crust called TECTONIC ACTIVITY - these forces cause plates to move
- when plates move toward each other COMPRESSIONAL FORCES result - when they move apart TENSIONAL FORCES are created ** see Fig. 1-9 p.11 & Fig.1-10 p.12 in text
Plate Tectonics Plate movement, which results from the movement of liquid rock in Earth s interior, produces many of the landscape features which we see around such as mountains.
MOUNTAIN BUILDING - compressional and tensional forces result in changes to the shape of the land - continental plates collide with oceanic plates - this results in rock layers bending causing mountains
3 Types of Mountains I. Fold Mountains II. Fault Mountains III. Volcanic Mountains
I. Fold Mountains - rock layers have wave-like appearance - the peak or upturn in the land is an ANTICLINE - the downturn or trough of the wave is the SYNCLINE
I. Fold Mountains (cont d) Rock strata Anticline
Fold Mountains (cont d) Rock strata Syncline
Anticline or Syncline?
II. Fault Mountains - if the tensional/compressional forces on the rock are so intense or the rock is brittle, the rock may fracture or break apart - called FAULTING
II. Fault Mountains (cont d) - faults can be deep or shallow; short or long - usu. displacement along the fault line the direction of displacement determines the type of fault -- there are 3 general types
II. Fault Mountains (cont d) 3 General Types of Faults i. Normal ii. Reverse iii. Overthrust
II. Fault Mountains (cont d) i. Normal Fault - results from vertical displacement, i.e. a plate on one side drops below the other - tensional forces - if 2 parallel normal faults occur near each other the piece of crust between the faults drop - this creates a RIFT VALLEY (see p.15 Fig. 1-13)
II. Fault Mountains (cont d) ii. Reverse Fault - results from compressional forces - one side is pushed up over the other - if 2 parallel reverse faults occur, a BLOCK MOUNTAIN may result - (see p.15 Fig. 1-13)
II. Fault Mountains (cont d) iii. Overthrust Fault - when a folded plate encounters a fault - the folded layers are thrust over the other side of the fault - (see p.15 Fig. 1-13)
III. Volcanic Mountains - magma reaches surface through crack or fracture in the crust - LAVA (liquid rock), gases and molten rock fragments called ASH OR CINDERS flow through fracture - these flows can be either violent eruptions or mild, slow flows - landform associated with these flows is VOLCANOES these result when lava, ash and cinders flow through single opening called a VENT
III. Volcanic Mountains (cont d) 3 Types of Volcanoes 1. Shield Cone - lava flows slowly; mild eruptions - consists of alternating layers of lava - cones are broad with gently flowing sides ex. Mauna Loa largest volcano in world
III. Volcanic Mountains (cont d) 2. Ash-and-Cinder Cone - explosive eruptions send lava to great heights - it cools and falls back to earth in form of ash and cinders (PYROCLASTICS) - these materials build up around the vent forming steep-sided cone - ex. Paricutin in Mexico started erupting in 1942 and finished 1952 -- 610 m high
III. Volcanic Mountains (cont d) 3. Composite Cone - comprised of alternating layers of lava and ash and cinder - eruptions sometimes violent and other times gentle flows - not as steep as ash-and-cinder cones & not as gently sloped as shield cones - exs. Mount Fuji (Japan), Mount Vesuvius (Italy) ** Read Mount Pinatubo Case Study p. 17 **