UNIT 1 - Major Land and Water Forms

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1 UNIT 1 - Major Land and Water Forms Chapter 1 - Landform Patterns and Processes Topography the natural and human features of the Earth s surface. ie. Surface features elevation - the height of a particular point of land above sea level relief - the change in elevation over a given distance Hill - areas of high relief with elevations no higher than m Mountain - areas of high relief with elevations higher than m - most occur in long chains called ranges (usually along margins of continents) Plain - Level land - frequently found along coastal areas or at lower elevations - very gentle slope and no local a relief for thirty metres or more Plateau an extensive, relatively flat upland area have been raised upward into higher elevations by movements of the Earth s crust often found in interiors of continents because they are often deeply eroded by stream valleys, they have more rugged appearances than plains

2 Plate Tectonics and Continental Drift Originally a theory by German scientist Alfred Wegener Believed at one point in the earth s history we were one giant supercontinent known as Pangea. The theory was backed up based on how the continents of Africa and South America fit together, many similar ferns and reptiles in many different continents,and same types of rocks on continents close to each other (yet separated by an ocean) But Wegener had an issue trying to explain what actually moved the continents, Later it was discovered that tectonic plates move or float on top of the upper mantle. However they do not float freely. The plates are forced in specific directions by the flow of magma beneath. Plates move with the flow of magma. The magma closer to the core heats and then rises towards the surface as its density decreases. Once the rising magma reaches thecrust it moves in opposite directions. The magma forms convectional currents. This then is the power that moves the tectonic plates. Just like boiling water.

3 Compressional force a force pushing into a part of the earth s crust, causing it to buckle plates move towards one another, squeezing together Tensional force a stretching force in the earth s surface which may cause faulting plates break apart, moving away from or past each other, which may form a trench as one plate drops downward Mountain building Fold Mountains - an upland area formed by the buckling of earth s crust. Many fold mountains are associated with destructive or collision margins of plates. - amount and extent of force and pressure, can create simple or complex forms.

4 Anticline - An arch-like upfold in buckled, bent, or contorted rock. - looks like the letter A Syncline - a downfold of rock layers. - looks like a S mile Mountains Formed by Faulting Faulting - A fracture in a rock formation along which there has been movement of the blocks of rock on either side of the plane of fracture. Normal Fault A fault in which rocks have moved down the slope of the fault Reverse Fault A fault, perhaps caused by a compressional force, where movement is up, rather than down, the face over which movement occurs Overthrust Fault A fault that has previously undergone folding, with one set of rock layers pushed up and thrust over other rock layers.

5 Mountains Formed by Volcanoes Along plate boundaries, heat is generated because of friction, pressure, and decay of radioactive materials. Intense heat melts rock beneath the crust producing magma If it reaches the surface through fractures or vents, extrusive volcanic activity takes place. Terms: Lava - liquid rock Ash (cinder) - small molten rock fragments Vent - Single opening through which the volcanic products erupt Mild volcanic eruptions thin, liquid lava flows small amounts of gas Explosive volcanic eruptions thick lava flows large quantities of gas, ash and cinders Why do volcanoes erupt? - It is driven by buoyancy and gas pressure - Molten rock, which is lighter than the surrounding solid rock, forces its way upward and may ultimately break through zones of weaknesses in the Earth's crust. - If so, an eruption begins: The molten rock may pour from the vent as non-explosive lava flows - Or if may shoot violently into the air as dense clouds of lava

6 fragments. - Molten rock below the surface of the Earth that rises in volcanic vents is known as magma. - After it erupts from a volcano it is called lava. - The explosive quality of the volcano is directly related to the thickness of the the lava. This lava does not flow easily out of some openings, tending to solidify and plug the opening. - Pressure builds and as a result trapped material explodes through the passageway. Three types of Volcanic Cones : Ash and Cinder Cone eruptions consist mainly of ash and cinders thick, slow flowing, rapidly solidifying lava shape is symmetrical steep sides large crater Shield Cone usually milder eruption little or no ash and cinders very thin, liquid lavas broad, flat cones

7 Composite Cone undergoes periods of both explosive and quiet activity. layers of ash and cinders intermixed with layers of lava. weak spots may develop on sides with smaller lava flows forming smaller craters.

8 Chapter 2 - Wearing Down Landforms: Rivers and Ice Weathering vs. Erosion Weathering is the breakdown of rock and minerals. Erosion The movement of these weathered materials Two types of erosion: Deposition - occurs when the eroded material is dropped in a new location. Transportation - When weathered material is moved from one area to another. Physical Weathering vs. Chemical Weathering Physical weathering is the breakdown of rock and minerals by mechanical stress Chemical weathering breaks down rock with chemical reactions often including water. Types of Physical Weathering Frost fracture the expansion of freezing water that causes rocks to crack. Heat expansion rocks can expand and subsequently fracture. Plant growth expansion due to root growth. Burrowing animals - tunneling animals can increase the size of existing cracks

9 Exfoliation as internal pressure is released from certain rocks, it can cause layers to split and fall off. Types of Chemical Weathering Chemical weathering is the breakdown of rocks and minerals by chemical reactions and usually involves the action of rainwater. There are three different types of chemical weathering described below: Solutions: The formation of solution s as rainwater absorbs CO2, SO2, and other chemicals from the atmosphere along with organic acids from the soil, which then reacts with rock and minerals causing some to dissolve and move away. Hydrolysis, like the first process, involves the minerals in solution. In this case, carbonic acid reacts with silicates in some rocks leaving a soft clay from which potassium, sodium and magnesium are subsequently leached. Oxidation is the reaction of metallic minerals to oxygen (mainly in water). This results in the formation of oxides, which tend to be softer than the original mineral. For example, rust on iron.