Transcript LANDFORMS
LANDFORMS
Patterns and Processes
Structure
• • • From the surface, the Earth is a planet of continents and oceans.
There is constant motion on the earth’s surface.
Seismology is the study of earthquakes. Scientists use seismology to see into the interior of the Earth.
Structure of Earth’s Interior and Surface (pp. 4-9)
Structural Zones of the Earth
• Inner Core - 2700 km - Solid Fe with some Ni - 4000 to 6000 °C • Outer Core - 2300km - Molten Fe with some Ni - over 4000 °C
Structural Zones cont.
• Mantle - 2900 km - Divided into lower and upper layers - largely solid except for the upper 200 300km of upper layer called the ASTHENOSPHERE which is in a plastic like state.
- Made mostly of magnesium and iron silicates
Structural Zones cont.
• Mohorovicic Discontinuity - The boundary between the mantle and the lithosphere, at which earthquake waves change speeds.
- Was discovered in 1909 by Andrija Mohorovicic, a Yugoslavian seismologist.
Structural Zones cont.
• Lithosphere - 1-100km - made up of the lightest elements and compounds - can be divided into 2 layers, one under ocean basins (sima) and one making up the continents (sial) - Rocks of continents are also called the crust
“Rocks and Minerals”
• • • Rocks are formed by minerals mixing together and solidifying due to physical or chemical processes. Three categories of rocks: (see page 6) 1. Igneous 2. Sedimentary 3. Metamorphic Construct a table with these headings: rock category, describe formation, possible location.
Topography
• • Topography refers to the physical / landform features of the earths surface.
Mt Everest is 8848 m above sea level. The Marianas Trench is 11,034 below sea level. Topography is all the features in between.
Topography
Pangaea "all the earth"
• In 1915, the German geologist and meteorologist Alfred Wegener (1880-1930) first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid core.
• Wegener hypothesized that there was an original, gigantic supercontinent 200 million years ago, which he named Pangaea, meaning "All-earth". Pangaea was a supercontinent consisting of all of Earth's land masses.
• Pangaea started to break up into two smaller supercontinents, called Laurasia and Gondwanaland
Plate Tectonics
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PLATE TECTONICS
The theory of plate tectonics (meaning "plate structure") was developed in the 1960's. This theory explains the movement of the Earth's and also explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and many other geologic phenomenon.
• The plates are moving at a speed that has been estimated at 1 to 10 cm per year. Most of the Earth's seismic activity (volcanoes and earthquakes) occurs at the plate boundaries as they interact.
The rocks of Gros Morne National Park and adjacent parts of western Newfoundland are world-renowned for the light they shed on the geological evolution of ancient mountain belts. The geology of the park illustrates the concept of plate tectonics, one of the most important ideas in modern science. This is one of the main reasons why Gros Morne National Park has been designated a World Heritage Site by UNESCO (the United Nations Education, Scientific, and Cultural Organization).
Compressional Force
----> compressional <----- When plates move towards each other they create compressional force which causes rock layers to bend, warp, or be pushed upwards.
Compressional forces are forces that squeeze crustal rock together.
Formation of the Himalaya Mountains
http://www.ascensiongateway.com/blog/uploaded_images/himalayas-716479.JPG
Tensional Force
<------- tensional-----------> When plates break apart, moving away from each other, they create tensional force. Tensional forces are forces that pull crustal rocks apart.
Sometimes these tensional forces are so strong that an opening is created allowing the magma or lava to force it’s way up through. This lava cools and forms a ridge. These zones are referred to as RIDGE ZONES
Crustal Movement
Fold Mountains
Fold Mountains
• • • Most Major Mountain ranges were formed by folding. The collision of continental plates causes the thin crust (lithosphere) to bend. For example the Appalachian mountains and the atlas mountains were formed by folding when North America and Africa collided 400 million years ago. cdli.ca
• All rock that is put under extreme pressure for long periods of time (thousands or millions of years) will fold like clay. • Folding is a process in which the Earth's plates are pushed together in a roller coaster like series of high points and low points. • Folding bends many layers of rocks without breaking them Anticlines are folds in rocks that bend upwards. Synclines are folds in rocks that bend downwards. Joints are parallel cracks in rocks.
An anticline is a convex up fold in rock that resembles an arch like structure with the rock beds (or limbs) dipping way from the center of the structure
A
syncline
is a fold where the rock layers are warped downward. Both anticlines and synclines are the result of compressional stress.
Picture of Syncline fold in Quebec
Mountains by Faulting
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Faults
form in rocks when the stresses overcome the internal strength of the rock resulting in a fracture. A fault can be defined as the displacement of once connected blocks of rock along a fault plane. This can occur in any direction with the blocks moving away from each other. Faults occur from both tensional and compressional forces.
Normal Faults occur when tensional forces act in opposite directions and cause one slab of the rock to be displaced up and the other slab down.
Faults cont.
• A Rift Valley is a valley bounded by two roughly parallel faults formed when the rocks of its base moved down the fault plane • Block Mountains are a mass of upland, bounded by faults. The surrounding rocks may have sunk, the mountain block may have risen, or both may have occurred
Reverse Faults develop when compressional forces exist. Compression causes one block to be pushed up and over the other block.
Overthrust Fault is a fault that has previously undergone folding, with one set of rock layers pushed up and on other rock layers
Mountains by Volcanoes
Ash and Cinder Cones
• A cinder cone is a volcanic cone built almost entirely of loose volcanic fragments called cinders. They are built from particles and blobs of congealed lava ejected from a single vent. • As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone.
• Most cinder cones have a bowl-shaped crater at the summit. • Cinder cones rarely rise more than 300-500 m or so above their surroundings, and, being unconsolidated, tend to erode rapidly unless further eruptions occur. • Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world.
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Shield Cones
Shield cones (shield volcanoes). Primarily a liquid flow event. Basic lavas, having a lower viscosity, are very fluid. • Such flows cannot pile up to form steep slopes. • They spread out, travel fast, and go far, eventually cooling into thin, nearly horizontal sheets of rock.
• As successive layers are stacked up from hundreds, if not thousands, of eruptions, a gently sloping cone, or flattened domical mountain develops, with its characteristic caldera at the summit, and pit craters along some of the rift zones--a shield volcano.
Internal structure of a typical shield volcano
COMPOSITE CONES
• Composite cones are volcanic cones made up of alternating layers of lava and rock particles. Weak points may develop along the sides of composite cones. Lava flows out of these weak points to form smaller cones.
• Composite volcanoes represent some of the greatest and most violent types of volcanoes on earth's surface. A typically composite volcano is a steep sided, large structure with a symmetrical cone. The cone is built from alternating layers of lava flow, volcanic ash, cinders, blocks, and bombs.
• There are two routes lava can flow from a composite volcano. • The first is by breaking through the crater walls from fissures on the sides of the cone. • The lava then cools once it has filled the fissures and acts as a dike. This cooling activity acts as a benefit to the cone because it adds in its strength and stability. • The other direction of flow is simply from the crater at the opening of the volcano.
• The most distinctive characteristic of the composite volcano is
the conduit system.
The conduit system allows for a magma reservoir deep inside the earth's crust. The pressure and the volume of magma is allowed to build up under the crust until it is released in a violent eruption. The eruptions of ash, lava, and cinder are responsible for the continuing growth of a volcano.