Download Stages of Tukituki Evolution

Stages of Tukituki Evolution
Stage one
Stage 2
Stage 3
Stage one
• 100 million years ago a deep ocean trench or geosyncline was present in the ocean. This geosyncline accumulated silt in the form of sand and
mudstone. The sand and mudstone sediment was
deposited due to fluvial transportation. With the
pressure of the ocean above this sand and
mudstone was compacted into sedimentary rock
form. Due to the relative fluidity of the sediment
at this time it stratified itself this is shown in the
diagram by the different layers shown.
Stage 2
• The earth’s mantle is extremely hot and this heat
create’s convection currents. These convection currents
move the earths continental plates as the float on the
convection currents. This is known as continental drift.
In this scenario we can see the indo-Australian plate
colliding with the pacific plate. Due to this collision
zone we get a squeezing motion on the sand and
mudstone sediment which has been deposited in the
syncline. When a sedimentary rock is put under
extreme pressure it changes form to metamorphic in
this case we see a change to the metamorphic rock of
Greywacke. The squeezing movement gets
concentrated on the Mohaka and Ruahine fault line.
Stage 2
• Once the pressure builds up we begin to see a
process called faulting. This faulting resulted
in a rapid uplift of the sediment which was
once in the geo-syncline. This rapid uplift
formed the Ruahine range which is an
example of a horst. You can see by the
diagram that the horst is still stratified in mud
and sandstone layers.
Stage 3
• From 5 million years till present day we see the formed
Ruahine range which is now under-going a number of
surface process.
• The predominant weather system in New Zealand is
westerly which gets blown of the Tasman Sea. This
moisture rich weather hits the Ruahine range is forced
to rise where it cools and condenses and brings about
Orographic rain.
• This Orographic rain fuels the water supply to the
Ruahine range and creates tributaries which eventually
lead to another major feature of the Tukituki
catchment that being the river itself.
Stage 3
• The tributaries travel down stream carrying
sediment in the form of Greywacke rocks eroding
the Ruahine range. The transported sediment
which comes from the Ruahine range is the
reason for the alluvial fertile soils in which the
central catchment region contains.
• The extreme high altitude of the Ruahine range
also creates an area for freeze thaw this cracks
rocks and erodes them. These two types of
erosion lead to the scree or vertical erosion which
is visible on the Ruahine range.
Stage 3
• The continuing plate movement which created
the horst has also lead to the fold mountains
of the eastern hill country. The new rangitoto
and elsthorpe anticline shoulder the atua
synline where the Tukituki river flows. The
Eastern hill country has been bought about
due to the softness of the rock which allows it
to be folded without snapping. The soil here is
fertile but due to poor drainage doesn’t grow
well.