Fiordand National Park (New Zealand): Glacial Valleys
1. Zoom from Fedchenko Glacier (Tajikistan) to Fiordland National Park (New
Zealand)
2. In the last lecture we looked at the power of alpine glaciers, carrying a
continuous stream of ice and rock from the tops of mountain ranges to the
bottom. In this lecture, we will look at what is left over when the ice is gone.
a. Glacial valley – U-shaped – explain how it forms
b. Fjord (why is it flooded? 400 ft sea level rise!)
3. Fiordland National Park (South Island of New Zealand) – classic and
spectacular example
a. Broad expanse, many sounds [show map], drops steeply to the sea.
b. Milford Sound is the most spectacular, but there are others as well.
c. Mitre Peak is the tallest continuous sea cliff in the world – rising 1683
m from Milford Sound.
d. Cirques, tarns, hanging valleys, horns, arêtes, waterfalls
4. Describe the Southern Alps
a. New Zealand isn’t too far south (45 deg – as far south as Maine is
north), but the mountains rise quickly to over 10,000 feet
b. Over 3000 glaciers – longest is Tasman glacier (29 km)
c. First identified by explorer Abel tasman in 1642, but named by
Captain Cook in 1770.
5. Why are the Southern Alps even there? Because a plate boundary runs right
through New Zealand!
a. Explain the Alpine Fault (saw it earlier in the “Top 5” for the San
Andreas Fault)
i. 4 big earthquakes in 1100, 1450, 1620 and 1717 AD – we are
overdue!!
b. As part of Australia moving northward away from Antarctica, the
Tasman Sea and the top half of New Zealand are being pushed to the
northeast at the same time that the Pacific Plate is pushing westward
from the east.
c. This causes displacement across alpine fault of 1-10 cm/yr over the
past 23 Ma.
i. Rock at the north end of the southern island, like at Nelson, is
the same as rock at the southern end of the island.
d. The compression has pushed up the Southern Alps.
e. This ALSO explains the steep dropoff at the Fiordland coast, because
the fault runs right along it, and on the north side are rocks that
recently were in the sea to the south.
6. But there is one more important component to the stunning appearance of
places like Milford Sound. The rock of the steep cliffs is granite.
a. Remember Grand Canyon? Weak rocks like shales and mudstones are
easily weathered and tend to have shallow slopes. Tougher rocks have
steep slopes.
b. There are plenty of different kinds of rocks in Fiordland – this has a
long history of deposition of sedimentary rocks. But it is the granite
that is tough and strong and has steep slopes.
i. [I grew up part of the time in new Hampshire – lots of granite,
like the Old Man of the Mountain]
ii. What do the Appalachians of New Hampshire and the Southern
Alps have in common?
iii. They are both mountain ranges that were once much taller,
and have been eroded away, exposing the deep core of the
mountains.
iv. Southern alps may have had as much as 20,000 ft (6 km) of
sedimentary rock eroded away.
c. Explain the process of making and exposing granite.
i. Mountain collision, rocks pushed down where they heat up
ii. Certain minerals begin to melt  composition of granite.
iii. The melt rises up, but cools inside mountain range before it
can reach the surface  granite batholith
iv. Isostatic rebound as surface rocks erode.
v. Eventual exposure of granite rock that was once many miles
below the surface
d. Other rocks there as well, however. One of the most culturally
important is a type of nephrite jade, called greenstone (called
Pounamu in the Maori language).
i. It is a important and highly prized commodity in Maori culture,
and was used to make jewelry, weapons, tools and talismans.
Many of the traditional designs have survived and nowadays,
you can see beautiful greenstone carvings in most New Zealand
craft and tourist shops.
ii. Only found along the coasts of Fiordland National Park.
7. Top 5:
a. Yosemite (California) – classic example of a glacial valley, though
many others are larger; due to photography of Ansel Adams;
Halfdome; El Capitan is over 1 km vertical face (granite!); Yosemite is
classic example of exposure of a granite batholith (Sierra Nevada
batholith)
b. Norwegian fjords, like Geirangerfjord and Sognefjord – where the
word “fjord” came from. Geirangerfjord is the most visited fjord in
Norway. Sognefjord is the longest – stretches 205 km inland!
c. Scoresby Sund (Greenland) – world’s longest fjord – 350 km long!
d. Gimmelwald and Grindelwald – beautiful glacial valleys around the
Swiss Alp mts (Munch, Eiger, Jungfrau)
Questions:
1) Why do you think that the granite rock of the cliffs of Milford Sound are
stronger and more resistant to weathering than sedimentary rocks?
2) What do you think will happen to New Zealand if earthquakes keep occurring
along the Alpine Fault?