The the Pacific Plate. It is around 600

The Alpine Fault Draft/Notes:

What is the Alpine
Fault?

The
Alpine Fault is what it is today because of a multitude of different natural
processes. Firstly, the earth is made up of different layers, and on this
outermost layer, the crust, there are many different tectonic plates. The
innermost layer of the earth, the inner core, is as hot as the surface of the
sun, and is made up of solid iron, nickel alloy and a lighter element. The next
layer is the outer core, which is made of liquid iron and nickel alloy. The
outer core is cooler than the inner core, giving it more mobility and the
ability to generate electrical currents. The next layer is the mantle, the
largest and the most influential layer on plate tectonic movement. Within the
mantle is a process known as a convection current, made possible by the mantle’s
ability to flow. This current, as shown in the picture, operates by the less
dense, heated rock rising and the denser, cooler rock descending. The rock is
cooled because, as it rises, it moves further away from the outer and inner
core, and into the upper mantle, which is at a lower temperature than the lower
mantle. These convection currents move the tectonic plates either away, towards
or slide them past each other, causing faults. The tectonic plates make up the outermost
layer of the earth, the crust, which is relatively cold in comparison to the
others, and made of rock, making it solid.

The Alpine Fault is the land boundary between two of these tectonic
plates: the Australian Plate and the Pacific Plate. It is around 600 kilometres
long and runs along the spine of the South Island, Te Ika a Maui. In the last
900 years it has ruptured four times, each time causing around a magnitude 8
earthquake; there is also an estimated 30% chance of the Alpine Fault rupturing
again in the next 50 years, potentially producing another magnitude 8
earthquake, of which its effects could be felt as far away as Australia. The
Alpine Fault is also the line between the snowy Southern Alps and the western
coastal plains, as seen very clearly from the satellite image below.

The Alpine Fault is a right-lateral strike-slip, or dextral,
fault. A strike slip fault is where the forces pushing the rock are mostly
horizontal, causing them to move side by side to the fault line. Right-lateral
strike-slip faults can be described as if someone were looking down the fault’s
length; they would see the right block moving towards them, and the left block
moving away from them. It is this type of fault because of the Australian
plate’s horizontal movement to the north east, while the Pacific plate is being
pushed horizontally and upwards against the Australian plate.

The Alpine Fault has had a large effect on many surface
features of the South Island: lakes, glaciers and mountains alike. It has formed
and uplifted the Southern Alps, a major surface feature of the South Island, at
a rapid rate: around ten millimetres of uplift a year for the Mount Cook region
of the Southern Alps, and five millimetres per year for the West Side and
Kaikoura Ranges. However, this movement isn’t constant, and instead happens
suddenly during earthquakes every few hundred years. In total, over the last
2-3 million years, the Mount Cook region of the Southern Alps may have been
uplifted by nearly 20,000 metres. The Southern Alps has then formed many other
important surface features, such as Fox Glacier and Lake Wanaka. Yet the Alpine
Fault doesn’t just uplift regions, it also creates large amounts of horizontal
movement. The Alpine Fault moves around 30 metres per 1000 years, which is
quite fast on global standards. A new study which emerged in 2016 showed new
evidence that the fault running through the South Island was record breaking.
Previously it had been thought that the Alpine Fault had moved around 450
kilometres, this being found out by identifying the offset between distinctive
rocks on either side of the fault. The newly recognized total movement over the
last 25 million years, based on the new study’s research, is 700 kilometres.
This is ground breaking in the field of geology, with this movement being much
more than previously thought possible. The previously largest tectonic, on land
movement was 475 kilometres, on the Altyn Tagh fault in Tibet.

This movement has had a big effect on surface features, and
many main features of the South Island have been directly influenced by the
Alpine Fault. A new study shows

Its size, history, ability to be seen clearly from space,
and potential to spawn massive natural disasters, makes the Alpine Fault a
major, influential landmark in New Zealand.

 

Southern Alps

The Southern Alps are the result of collisions between the
Australian and Pacific Plate, but has become what it is today because of
different internal and external processes. The Alpine Fault uplifts the Southern
Alps at a rapid rate, and if not for the erosion rate being near the same, this
mountain range could be 20 kilometres tall at its peak. This uplift is because of
the two tectonic plates colliding and pushing together, building up large
amounts of pressure that release as earthquakes, and push up layers of the
crust to form mountains. However, because of erosion, its highest point, the
Aoraki/Mount Cook region, is only 3,724 metres, and is not constantly
increasing in size. There are differing types of erosion, however the one that
erodes the Southern Alps is mechanical/physical weathering. This is when the
rain seeps into the cracks of rocks, within the mountain, in the day, and then
freezes over night. As it freezes, the water expands by around 4%. The ice then
melts, causing the rocks to contract and, after years of this process repeating
over and over, fracture, causing it to become loose rock. This erosion is key
when describing the formation of the Southern Alps as it is today.