World Geography 3202 Unit 1. Ch. 1: Landform Patterns and Processes

Transcription

1 World Geography 3202 Unit 1 Ch. 1: Landform Patterns and Processes

2 - 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

3 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

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5 HOW LANDSCAPES CHANGE 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

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7 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

8 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

9 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)

10 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

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13 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

14 - 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

15 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.

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17 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

18 3 Types of Mountains I. Fold Mountains II. Fault Mountains III. Volcanic Mountains

19 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

20 Formation - Fold mountains form when two tectonic plates move together (a convergent plate boundary or compressional action). - Fold mountains form from sedimentary rocks that accumulate along the margins of continents. - When plates and the continents riding on them collide, the accumulated layers of rock may crumple and fold like a tablecloth that is pushed across a table, particularly if there is a mechanically weak layer such as salt.

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26 I. Fold Mountains (cont d) Rock strata Anticline

27 Fold Mountains (cont d) Rock strata Syncline

28 Anticline or Syncline?

29 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

30 II. Fault Mountains (cont d) - faults can be deep or shallow; short or long - typically displacement occurs along the fault line - the direction of displacement determines the type of fault -- there are 3 general types

31 II. Fault Mountains (cont d) Four General Types of Faults i. Normal ii. Reverse iii. Overthrust iv. Strike-Slip (will not be tested)

32 II. Fault Mountains (cont d) i. Normal Fault - results from vertical displacement, i.e. a plate on one side drops below the other - caused by tensional forces

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35 Horst and graben refer to regions that lie between normal faults and are either higher or lower than the area beyond the faults. A horst represents a block pushed upward by the faulting, and a graben is a block that has dropped due to the faulting.

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37 II. Fault Mountains (cont d) ii. Reverse Fault - results from compressional forces - one side is pushed up over the other resulting in a BLOCK MOUNTAIN.

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39 II. Fault Mountains (cont d) ii. Overthrust Fault - when a folded plate encounters a fault the folded layers are thrust over the other side of the fault

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43 Strike-Slip Fault

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46 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

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48 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

49 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 m high

50 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 **

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