The South Island High Country (SIHC)
The South island High Country (SIHC) is one of NewZealand’s most
distinctive landscapes. It is an area of mounatins that covers 70% of
the South Island. The land is very steep and rugged so it has very low
population density, less than one person per square kilometre. The
SIHC is located in the interior of the South Island strecthing from the
Tasman mountains in the north to Mt Aspiring in the south. As this
case-study includes detail on glacial processes, we will also include
the landforms of Fiordland.
South Island: 150 000 km2
South Island High Country: 105 000km2
The SIHC is a region of steep rugged mountains covered in snow all
year round. It has deep glacial velleys and fiords, densly forested
western slopes and tussock covered grassland east of the Alpine
Fault (or Main Divide). Some areas have very high rainfall, other
areas have very little.
Insert map of SIHC locate and label main mountains, lakes, rivers
and towns.
FQ What are the elements of the SIHC landscape?
FQ What processes have affected these elements?
Relief and Relief processes
The relief of the SIHC is dominated by rugged exposed mountains of
over 1000m elevation. These mountains form a long chain of peaks
called the Southern Alps which run the length of the South Island.
There are around 200 mountains of over 2300m. The highest peak is
Mt Cook at 3754m. These mountians have been heavily modified by
glacial and fluvial erosion.
The Southern Alps have been formed by the earth-building processes
of folding and faulting along the Alpine Fault. This fault runs over
550km from Milford Sound to Cook Strait. It is a reverse transform
fault.
Table of rock types and characteristics.
Rock Name
West Coast Granite
Haast Schists
Torlesse Greywacke
Type
Igneous
Metamorphic
Sedimentry
Age
Ancient
Young
Young
Quality
Very Hard
Hard
Soft
Model of Southern Alps cross-section showing rocktypes, fault
movement rate and named places.
In the past 75 million years the Indo-Australian and Pacific plates
have been colliding, forcing up the Torlesse and schist rocks on the
Pacific Plate above the granite rock on the Indo-Australian plate. As
well as vertical movement there has been a similar rate of horizontal
movement. (20mm/yr)
Glaciers
These are rivers of ice that carve valleys. Glaciers form when snow
collects in a hollow or depression on a mountain. As snow builds up,
the bottom layers are turned into ice. Eventually the ice layers build
up and gravity begins to move it down the mountain. The solid ice is
an extremely powerful agent of erosion. It can dislodge rocks from the
mountain and grind away at the valley walls. When glaciers melt
away during the Earth’s warm periods, they reveal a U-shaped valley
with very steep sides and a broad flat base.
Diagram of U-shaped valley.
The material that is eroded by glaciers is called morraine. Rocks that
fall on to the glacier or are eroded by it are transported down valley
by the slow movement of the ice. Eventually this rock reaches the
end of the glacier (snout). At this point the ice melts and the rocks are
deposited. When glaciers retreat during warm periods they leave a
large mound of rocks called terminal morraine. The eroded rocks that
are deposited on the side of the glacier leave mounds called lateral
morraine.
Sketch of Glacial landscape with named features.
Finger lakes occur when water is trapped on the base of a U-shaped
valley by the terminal morraine. They are long skinny and usually
quite shallow. Sometimes old glacial valleys on the coast are flooded
by seawater creating sounds or fiords.
Sketch of Key features of the SIHC showing very steep rugged peaks
- mount cook, tasman glacier, braided river – Tasman R., finger lake
– Pukaki trapped by morraine from last ice age 100 000 yrs ago
The SIHC has over a hundred glaciers currently eroding the
landscape. Some move quickly – The Franz Josef can move up to
4m per day, while others move more slowly – Tasman Glacier moves
less than 1m per day.. The glaciers have been shrinking due to the
slow increase in average temperatures, possibly brought about by
global warming.
The last major glacial period took place 18 000 years ago when the
earth was much cooler. The cold conditions meant a much greater
number of glaciers in the SIHC (and the world). Much of the earths
water was locked up as ice so sea levels were 150m lower. Glaciers
carved U-shaped valleys to the coast. These became flooded when
the sea levels rose again, forming fiords like Milford Sound.
Use information to create a three frame flowchart showing how a
glacial landscape feature has been formed.
Peri-glacial processes
The cold climate of the Southern Alps lead to a great deal of freezethaw erosion. This is when small cracks in rocks fill with rainwater.
When this water freezes in cold conditions it expands. This can widen
the crack and evenmtually break the rock apart.Big piles of broken
rock form at the base of cliffs forming scree slopes. These piles are
eventually moved by glaciers or rivers.
Fluvial erosion.
This is the re-shaping of the land by rivers. The southern alps
receives a great deal of rainfall, this must drain back to sealevel. As it
travels the river erodes rock and sediment on steep land and deposits
it on flat land. It is through this process that the Canterbury Plains and
Westland have been built up with material from the Southern Alps.
Sketch of river and floodplain in Dent
Climatic patterns and processes in the SIHC
Map showing four distinct climatic areas. W of Southern Alps – high
precip and cold, E of Southern Alps – midler, rainfall 1300 – 2000mm,
Central Otago – low rainfall 600mm-1000mm often drought.
Climate controls (things that influence climate)
Altitude : Temperature drops with increasing altitude, at the rate of
approximately 0.6 degrees per 100m gained. This explains why the
region experiences cold temperatures as much of the land is over
100m above sea level.
Relief: The high relief of the Southern Alps creates orographic rainfall.
The predominantly Westerly wind brings moist air from over the
Tasman Sea. This moist air is forced to rise by the Southern Alps
causing the moisture to condense and fall as rain on the western
slopes of the mountains. On the eastern slopes the air is much drier.
Latitude: The SIHC is found at mid-latitudes (41o – 45oS) so
temperatures are relatively mild (moderate) compared to those at the
equator or poles.
Distance from the Sea: The sea has a moderating affect on
temperatures. Places close to the sea like Milford Sound and
Christchurch have fewer extremes of temperature, whereas places a
long way from the coast can at different times be very cold and and
also very hot. There is often a big difference between day and night
temperatures and also between summer and winter temperatures as
land gaiins and loses heat much more rapidly than a large body of
water. Alexandra has recorded some of New zealand’s highest (35o)
and lowest (-15o) temperatures.
Complete climographs for SIHC sites from ESA revision book.
Vegetation patterns and processes
In the SIHC there are three distinct types of vegetation
Beech forest: Tall evergreen forest dominated by different types of
beech trees and other native trees and shrubs
Tussock: A hardy type of thick grass that copes with cold conditions.
Usually brown or gold in colour.
Alpine herbs and mosses: very small low-lying plants that can cope
with poor soil and harsh weather of the mountain environment.
There are two main patterns in the SIHC.
The western side of the southern alps is dominated by beech forest,
the eastern side is dominated by tussock, this is because beech
forest requires lots of rain to develop.
There is also a clear pattern as you climb a mountain in the SIHC.
Diagram of altitudinal zonation.
FQ How has the SIHC developed through time?
Stage One:
After millions of years of erosion and deposition, techtonic forces
pushed the Indo-Australian and Pacific Plates together. This collision
caused the uplift of ancient Gondwanaland sediments out of the sea.
Insert diagram of event
Stage Two:
Compression of the two plates formed the Alpine Fault and the
Southern Alps and also folded the Torlesse of the Southern Alps.
This soft rock was easily eroded by glacial and fluvial processes and
transported to the Canterbury Plains.
Insert diagram of event.
Stage three:
The glacial, fluvial and aeolian processes acting on the Alps
transported and depostied material to the Canterbury Plains where
alluvial gravel and loess built up.
Insert diagram here.
FQ How is the SIHC different in different parts?
Insert stylised oblique cross-section of Southern Alps showing
different rock types.
Add the following labels:
Climate colder temperatures at higher altitudes. More rain in west
compared to east. Glacial and periglacial processes dominate at high
altitude whereas fluvial dominates at low altitudes.
Vegetation beech forest on the west side, tussock on the east. More
growth on low altitudes compared to high altitudes
Relief different rock types under the surface of land. Different shaped
land forms – steep mountains in centre, flat plains on coast.
Soil steep land has thin soil while flat land has deep more developed
soil.
FQ How has human activity affected the SIHC
Extensive pastoralism
The SIHC has much land that is suitable for sheep farming. There is
only limited grass growth in the SIHC due to the cool temperatures
and variable rainfall on the eastern side. This means that farmers
require very large amounts of land to feed relativelt small amounts of
livestock. These farms are called ‘stations’ and are often over
50 000 hectares. The largest is Molesworth station. Sheep farming
dominates because the land is too rugged for cattle farming.
There are several impacts that sheep farming has on the land. Some
land has had to be cleared of forest to make way for grassland.
Farmers often move their stock into the hills when the grass on the
farm is running out, this is called transhumance. Also, many farmers
add fertiliser to the land to increase productivity. This is called topdressing. The fertiliser can affect streams by providing an excess of
nutrients that can result in weeds choking the stream.
Conservation.
It is important to remember that a great deal of the SIHC is protected
as either National or Forest Parks. This means that natural processes
can operate in these areas with little interference from people. Some
examples include Mt Cook and Westland National Park.
Tourism
A great deal of tourims takes place in the SIHC due to spectactular
scenery and landforms. People often use the SIHC for alpine
activities, sightseeing, tramping etc. These activities can affect the
land.
Alpine activities – roads carparks, tracks, buildings, deliberate
avalanches
Tramping – trampling native plants, walking tracks, litter
Sightseeing – litter, roads, carparks, tracks
Hydro-Electric Power Generation