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The Alpine Fault

NCEA surface features of NZ


on 25 October 2012

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Transcript of The Alpine Fault

surface featrues of NZ The Alpine Fault by Yancy Liu Throughout the west coast of the south island in NZ, many remarkably surface features of the landscape can be seen. For example: towering topography, glaciers that flow from elevations of 3,000m to near sea level, landslips into lakes or rivers, high continuous southern Alps, creeks,etc.
These surface features are all more or less effected by the significant geological strip--Alpine Fault. The Alpine fault is a right-lateral strike fault which runs among almost the entire South Island of New Zealand. It is a largely on-land segment lies between the Australian plate and the Pacific plate as a major plate boundary. CURRENT
LOOK It's fault line extends from the Wairau River valley in Marlborough and exits the island near Milford Sound. However, its different segments behave in different ways. In its southernmost part, it seems purely strike-slip with a very steeply dipping fault plane.
Ventral segments of the Alpine Fault have significant dip-slip movement on a moderately sloping lane because of compressive forces.
The northern segments produce mostly strike-slip movement, but at lower rates. Overall, The fault is actually a 20km-deep split in the Earth's crust which extends all the way down to the mantle, the second layer of the planet's interior which is made up of molten rock. How does it happen? Find out the internal process first! The Alpine Fault is a major transformation fault lies on a convergent plate boundary of Pacific and Australian plates.
These two tectonic plates into which the earth's crust broken up are constantly moving due to convection currents caused by the heat of the Earth's core.
The convection currents are basiclly process that hot objects rise.As they rise they move away from the core so they lose heat. Cool objects sink,moving back down to the heat source. It happens in mantal layer,where is more fluid, so the currents push the tectonic plates moving. Internal pr cess What's more, ways to release the pressure like plates converging and moving laterally past each other can also result in the movement of Alpine fault. For example, the rate of the horizontal lateral plate movement is quite fast by world standards- about 30 meters every 1000 years.
The convergences that caused the uplift and erosion of the crust are significant processes of Alpine fault's formation as well. These activities at east of the Alpine Fault has exhumed its rocks from deep within the crust. For instance, the rocks exposed in the glaciated valley below the Franz Josef glacier originated at more than 25 km depth within the crust and are now exposed at the surface. internal process External factors ------Creek For example, in Waikukupa Thrust area, the 'out of sequence ' of the same patterns on the rocks that partiality covered each other is related to rapid erosion by the Waikukupa River.
The progress is that water in the river smashes into coastal rocks, expanding and spliting the rock further, meanwhile the waves carrying gravels pack a punch to the palisades, wearing down hard rock layers and wash away softer rocks, distorting the clear figures on the surface of rock, making it more vague and smooth. If we say the internal influence is the crucial process that formed the Alpine fault, the external factors can also affect its formation. #1 CREEK
#3 CLIMATE External factors ------Creek Meanwhile, the large amounts of material carried by the rivers accumulate at certain area like mountain passes and a series of alluvial fan are formed alone the fault lines, causing the feature of staggered distribution that consists of faults triangles and alluvial fans of the Alpine fault. External factor ------Glacier The Glaciation also affect the Alpine Fault's formation, including the shape of the ranges on both sides of the fault and valleys between the mountains. The temperature and precipitation over the Alpine Fault zone create conditions favorable for glacial formation.
For instance, the West Coast's Fox and Franz Josef glaciers are two of the largest ones. These rivers of solid water that have huge mass slowly move forward under the force of gravity, 'scour 'the surface of rock.
The glaciers and rivers run downward the fault also remove the displaced crust and spread it out across the lowland plains or onto the sea floor. External factor ------climate Even the climate is affected. The wall of the Southern Alps across the prevailing westerly air-stream results in up to 10m of annual rainfall on the western side and less than 5% of this in the valleys to the east of the fault.
The intense water erosion on the western side of the Alps unbalance the tectonic forces leading to a greater concentration of deformation along the Alpine Fault, making the cliff of the fault retreat, slowing down its slope. Ultimately, this process could enable the fault scrap disappears. Tectonic plate movement along the Alpine Fault has had a number of major effects on the South Island’s surface features. So,how does the Alpine Fault change the surface features of the South Island? Southern Alps internal process The Australian plate moves towards the North as the Pacific plate is being thrust up over it. These tectonic plate movements along the Alpine Fault forms the Southern Alps.
Their squeezing motion also causes Alps uplift at a rate of about 8mm to 10mm a year because the convergence alone the Alpine fault has made crust disappeared in the central part of south island and much of this lost crust has been thickened to form a deep root to the Southern Alps. feature 1 Feature 1 Southern Alps external proces Weather that flows on to the West Coast is forced to rise over the Southern Alps, thereby cooling and dropping most of its moisture as rain and snow.
This process causes up to 30 metres of snow to fall on the catchment area of the glacier every year and result in the intense erosion of the north-eastern Alpine fault and counter the uplift of the Alps. Feature 2 Displacement In 1948 geologist Harold Wellman realised that rocks that were once adjacent to each other had been separated by 480 kilometres as a result of movement along the Alpine Fault since the landscape on these rocks at the opposite ends of the Alpine Fault is very similar. We can see the plates that component opposite sides have slid sideways past each other over the last 15–20 million years The rocks of southern part are similar to those found on the other side of the fault feature 3 Earthquake Since the Alpine fault spends much of its time, maybe hundred of years stuck at the joint, while Australia and pacific plates continue to move alone it (because of convection currents in the mantle rock on which the plates float), at some point, the strain on the stuck portion of it becomes too great and the fault slips . It is that sudden slip that causes the earthquake.
However, because of the constant speeds of plates movement for long periods of geological time, earthquakes on Alpine fault tend to occur at roughly regular intervals. Feature 4 Thermal pools The Alpine Fault – deep fractures in the rock caused by tectonic plate movement– provide channels for warm water to rise rapidly from depths where it has been heated. For example, At Hanmer, a range of thermal pools attract thousands every year.
The rainwater felt seeped down through fractured rock that formed by the fault movement to a depth of about two kilometres below the plains.Heat radiating from the Earth's core raises the temperature of the rainwater in the underground reservoir. This heated water then rises to the surface through the fault channels. feature 5 Landslides The Australian and pacific plates move along the Alpine Fault, causing earthquakes which are efficient triggers of extensive landslides, and could contribute a large proportion of the debris filling the Alpine valleys which is then redistributed further down during each subsequent flood.
Today, in the fault zone, the vegetation on river terraces, old slips and creek fans can be observed, helping build up a picture of past massive landslides due to Alpine Fault movement. SPLENDID SIGHT OF THE ALPINE FAULT--- THANKS FOR
WATCHING! 10/2012 The formation of the Alpine Fault What is it? When these two tectonic plates interact alone their "subduction" margins where the ocean floor descends into the Earth's mantle, they collide and scrape past each other, resulting important geological effects like earthquakes.
The rupture of rock caused by the earthquakes often reaches the surface and distorts the landscape, causing essential features of the fault. Like the visible edge of crustal ruptures is the fault line which is a big on-land segment, running among almost the whole south island; bit is marked by a change in slope or a long bank(a fault scarp). Convection
PROCESS SURFACE FEATURES The Pacific plate keeps steadily rotating anticlockwise (i.e 45 mm per year ) relative to the Australian plate at depth. (different rocks) The most recently rupture that accelerat the boundry's movement occurred in 1717AD, about 300 years ago. #WEATHERING
SCIENCE FOR THE NEW ZEALAND CURRICULUM BY Donald Reid.Geoffrey Groves.Colin Price.Lan Tennan
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