Download Diary 2 - LEARNZ

Diary 2
Published on LEARNZ (http://www.learnz.org.nz)
[1]
[2]
Date:
Tuesday, April 28, 2015
Field Trip Name:
Geohazards
Field Trip Place:
Marlborough
Weather:
Cold with showers
Where You Are:
Kaikōura
[3]
It felt more like winter today with a bitterly cold southerly wind blowing into
Kaikōura. Rob Langridge from GNS Science had arranged to meet you at the fur seal
colony not far from the town centre, so you had to brave the weather. Rob is an
earthquake geologist and he has planned your geological road trip to take in some
of the best geology of the area. You may have been wondering what seals have to
do with geology but then it all became clear when Rob took you up to the lookout
above the seal colony. This is a great place to get a view of marine terraces which
have been uplifted by plate tectonics.
Plates on the move
The Earth’s surface is divided into about seven large tectonic plates and several
smaller ones. The heat in the Earth’s molten mantle causes convection currents
which provide the energy to move these plates. This movement along plate
boundaries, and smaller breaks in the crust called faults, can lead to earthquakes
and volcanoes. Rob described this plate movement as the engine room for
earthquakes because this is where the energy for quakes comes from. If there was
no plate movement there would be no earthquakes.
It is also this movement that pushes land upwards. Rob showed you three different
terraces which were once wave cut platforms at sea level that have been pushed up
at different times in the past. These three terraces are evidence of three different
periods of uplift in our geologic history. You can see this in the video [4].
It had started to rain so we headed back to the shelter of the car to speak to Fordell
School in the audioconference. They had interesting questions about landslides. You
can listen to a recording [5] of this and the second audioconference with Valley
School about earthquakes.
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Earthquakes everyday
Earthquakes usually occur along faults which are areas of weakness in the rock
where movement can occur. Sometimes the blocks of rock on either side of a fault
suddenly shift to a new position in just a few seconds. This sudden release of
energy sends out waves, which are felt on the surface as an earthquake. The
strength of the earthquake depends on how much of the fault has shifted. Long fault
lines can produce larger earthquakes and the shaking lasts longer.
Earthquakes are possible in many parts of New Zealand and over 600 active faults
have been located across the country. Every year over 14,000 earthquakes occur in
New Zealand, meaning everyday there are earthquakes. About 100 to 150
earthquakes are large enough to be felt each year. We only know about the others
because they are recorded by seismographs.
Tsunami
As you headed back towards Kaikōura Rob talked about another type of geohazard
that could affect this area. Tsunami are waves created by movement under the sea
floor which displaces water in a surge or wave. Most large tsunami are caused by
undersea earthquakes but undersea landslides and volcanoes can also cause
tsunami.
Rob pointed out to sea where the Hope fault is and explained that if a rupture on
the fault happens there then it could generate a tsunami. Tsunami can be very
dangerous so it’s important to know what the warning signs are. If you are on the
coast and the sea suddenly draws back or if there is a large earthquake which
makes it difficult to stand then you should move to higher ground. The earthquake
may be a long way away so may not feel strong, but if it lasts for more than a
minute you should also move to higher ground. Sometimes there will be no other
warnings and sirens may not go off if the tsunami is generated close by. Tsunami
can travel at 600-800km/hour.
The Hope Fault
After talking about the Hope fault Rob was keen to take you to an area where you
can actually see the fault. The Hope fault branches off the Alpine fault and is
capable of producing large earthquakes. Inland from Kaikōura near Greenburn
Stream you can see an obvious line of raised ground. This is part of the Hope fault
scarp where land has been pushed up during earthquakes. Watch the video to see
this and find out more about this large active fault.
Landslides
Your time in Kaikōura had come to an end and you had to head north for the second
leg of your geologic road trip. As you drove along the coastal highway you could see
old landslides so Rob stopped to have a closer look. This area is prone to landslides
as it is steep, the forest has been removed for farming, and the rock is soft. Heavy
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Diary 2
Published on LEARNZ (http://www.learnz.org.nz)
rain and earthquakes can trigger landslides and many areas alongside the road had
slipped. Further north trees had been planted to try and stabilise the land. You can
watch the video [4] about landslides.
It started raining again as you drove to Blenheim and dark clouds made it feel much
later than it was. Hopefully the weather will be better tomorrow so you can get out
and about around Blenheim.
See you then,
Shelley the LEARNZ field trip teacher.
[6]
Rob and Shelley check out the view above the fur seal colony in Kaikōura.
Image: LEARNZ.
[7]
Looking out over the wave cut platform in Kaikōura. Image: LEARNZ.
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Diary 2
Published on LEARNZ (http://www.learnz.org.nz)
[8]
You can see three terraces on the hill in the middle of this photo. Each
terrace has been uplifted from the sea by plate movement. Image: LEARNZ.
[9]
The Seaward Kaikōura Range has been uplifted by plate tectonics and a
series of earthquakes over thousands of years. Which New Zealand
mountains are not the result of uplift? Image: LEARNZ.
[10]
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Diary 2
Published on LEARNZ (http://www.learnz.org.nz)
Rob takes Shelley and the ambassadors up to a lookout to find out more
about Kaikōura's geology. Image: LEARNZ.
[11]
The Hope fault can clearly be seen in this photograph as a hill or scarp.
Image: LEARNZ.
[12]
This landslide happened recently during heavy rain. Why do you think this
area is prone to landslides? Image: LEARNZ.
Page 5 of 6
Diary 2
Published on LEARNZ (http://www.learnz.org.nz)
[13]
You can see the size of this landslide with Rob standing at the toe of the
slide. How many metres long do you think it is? Image: LEARNZ.
Source URL: http://www.learnz.org.nz/geohazards152/diary-2
Links
[1] http://www.learnz.org.nz/printpdf/geohazards152/diary-2
[2] http://www.learnz.org.nz/print/901
[3] http://www.learnz.org.nz/sites/learnz.org.nz/files/gh152-diary-cam-2.mp4
[4] http://www.learnz.org.nz/geohazards152/videos
[5] http://geohazards152.learnz.org.nz/index.php?vft=geohazards152&dir=aud
io/arch&page=index
[6] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh152-d01-01.jpg
[7] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh152-d01-02.jpg
[8] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh152-d01-03.jpg
[9] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh152-d01-04.jpg
[10] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh152-d01-05.jpg
[11] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh152-d01-06.jpg
[12] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh152-d01-07.jpg
[13] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh152-d01-08.jpg
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