Chapter 1: Landforms Patterns & Processes Pg. 10-21
Video Time Physical Geography (6:02)
Introduction: Earth is dynamic it behaves as if it s a living organism. Some changes are rapid enough for us to see and record. i.e.: tidal activity, volcanic eruptions, flowing water/glaciers.
Other changes occur at an almost unnoticeable pace. i.e.: mountain building, continental movement, seafloor spreading.
Structures of the Earth 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 the THEORY OF CONTINENTAL DRIFT.
Theory of Continental Drift All continents were once joined together into super continent (PANGAEA) and surrounded by ocean (PANTHALASSA) ~ 200 million years ago Pangaea split into 2 sections which further segmented into present continents. (* see Fig. 1-8 p. 10 text *)
PANGAEA PANTHALASSA
Continents proposed to have drifted to present locations. Over time, it has been determined that the Earth s crust is not a singular piece of crustal material. Made up of pieces called PLATES.
Video Time Continental Drift (11:56)
World Plates
Plate Tectonics (1.1.1 1.1.3) Within the Earth there is energy; heat & pressure acting upon crust, called TECTONIC ACTIVITY. These forces cause plates to move.
Video Time Plate Tectonics (1:13) Plate Tectonics A Documentary (7:39)
Compressional Force When plates move toward each other.
Tensional Force Are created when plates move apart. Example:
Subduction Place where two tectonic plates collide. The more dense plate goes under, or subducts, to the other. ** see Fig. 1-9 p.11 & Fig.1-10 p.12 in text **
MOUNTAIN BUILDING (1.1.4) Compressional and tensional forces result in changes to the shape of the land. Continental plates collide with the oceanic plates. This results in rock layers bending causing MOUNTAINS.
3 Types of Mountains
1. Fold Mountains: (1.1.5) 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. Example:
Differentiate Anti-cline and Syncline Anti-Cline: It is the peak (top) of a folded mountain An arch-like upfold Top of the A Syncline: It is the bottom or the valley A downfold of rock layers Bottom or the S
Anticline or Syncline?
Video Time Mountain Fold (2:17)
2. 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. This results in the creation of FAULTS.
Faults can be deep or shallow; short or long. Usually displacement along the fault line. The direction of displacement determines the type of fault.
3 General Types of Faults
A. Normal Fault: (1.1.6) Results from TENSIONAL FORCES. (a plate on one side drops below the other) Example:
If 2 parallel normal faults occur near each other, the piece of crust between the faults can EITHER: 1. Drop, which creates a RIFT VALLEY. Example:
2. Rise, forming a BLOCK MOUNTAIN. (see p.15 Fig. 1-13) Example:
B. Reverse Fault: (1.1.7) Results from COMPRESSIONAL forces (one side is pushed up over the other.) Example:
C. Overthrust Fault: (1.1.7) When a FOLDED plate encounters a fault. The folded layers are thrust over the other side of the fault. Example: Fig. A on page 15.
Video Time Mountain Fault (1:24)
3. Volcanic Mountains: (1.1.8, 1.1.9, 1.1.10) 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.
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. Example: Fig. C on pg 16.
Mauna Loa largest volcano
2. Ash-and-Cinder Cone: Explosive eruptions send lava to great heights. (lots of smoke) 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. Example: Fig A on pg 16.
Paricutin, Mexico: 1942-1952
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. Example: Fig B on pg 16.
Mount Fuji, Japan Mount Vesuvius. Italy
Other Stuff Objective 1.1.10: pg. 12. Objective 1.1.11: pgs. 8 9. ** Read Mount Pinatubo Case Study p. 17 **
Conclusion: Most active volcanoes are located in the mountain ranges on the margin of continents. Most mountain chains are formed on the edges of tectonic plates, where plates collide, slide past each other, are pulled apart, or one plate is subducted below another. It is here that volcanic activity occurs because breaks in the crust allow molten rock and gasses to reach the surface.