Uluru/Ayers Rock (Australia): Inselbergs
1. Zoom from Bryce Canyon to Uluru, Australia
2. Remember we talked about the global pattern of air circulation generally
controlling which parts of the world are wet or dry. Australia is centered at
about 30deg south, so it is exceedingly dry. Most of Australia is considered to
be desert.
a. If you fly in to Alice Springs, the largest city in the Central Australian
Desert, and drive south, you go across a long flat dry region over 200
miles until you see something rising up out of the desert floor. On a
clear day, you can see Uluru, or Ayers Rock, from XXX miles away.
b. It is the opposite experience of driving to the Grand Canyon or Bryce
Canyon, where you are suddenly met with the spectacular view there.
In this case, as you drive toward Uluru, you gradually, slowly begin to
realize how enormous it is.
c. Uluru is an example of an inselberg (means “island mountain” – it is a
single rock that has resisted erosion, compared to the surrounding
rock layers. As a result, as the surrounding ground has weathered and
washed or blown away, Uluru has remained, and in fact, has grown
continuously relative to the surrounding rock.
d. A word about names: known to native aboriginals (the Pitjantjatjara)
as Uluru. On 19 July 1873, the surveyor William Gosse sighted the
landmark and named it Ayers Rock in honor of the then Chief
Secretary of South Australia, Sir Henry Ayers. Since 2002, it has had
the official dual name of Uluru/Ayers Rock.
e. Uluru rises about 350 m (>1140 ft) above the surrounding plain. Most
of its bulk is still buried, and it is estimated that it extends at least
another 2.5 km underground. It is about a 6 mile walk around it.
f. Ayers Rock is sometimes called a monolith, but this doesn’t have a
unique meaning. What makes Uluru remarkable, as an inselberg, is
how resistant it is to erosion. Rocks will usually weather along joints
or bedding planes, causing a rapid destruction of exposed rock.
Neither happens with Uluru – there are no obvious sets joints. There
are bedding planes evident – in fact, they are vertical (!!!). But there is
relatively little weathering around them, so there is no developed
patterns of gullies and no significant soil development.
3. Ayers Rock has a counterpart: About 25 km to the west is a set of similarly
rounded hills rising up out of the plains, called Kata Tjuta, or The Olgas. In
fact, they are all part of the same Uluru-Kata Tjuta National Park.
a. Kata Tjuta (which means “many heads”) consists of a set of hills,
compared to the single rock of Uluru. The colors of Kata Tjuta are also
different from Uluru, and it is clear that they are made out of a
different kind of rock.
b. But the two are clearly related, because there are very few places in
the world that look like this. So, the question is, how did these massive
rocks end up sitting high above the desert floor? How does something
like this form?
4. To begin with, the rocks in this region are old. Very old. Australia has some of
the oldest rocks in the world, dating back to more than 4 billion years. These
kinds of very ancient rocks are buried deep beneath the surface – in this
region, these “basement” rocks are 1-1.5 billion years old. The surface rocks
are younger, but still very old.
a. Uluru is made of a type of sandstone called arkose. We can look at the
characteristics of the sand grains within it to do some detective work
that might tell us how Uluru formed.
b. Arkose sandstone contains grains that are angular and sharp-edged.
c. Take a look at beach sand under a microscope: smooth and rounded
grains  from tumbling down rivers or smashed by waves. Sandstone
that forms from ocean beaches contains these smooth, round grains.
d. So, arkose is made from sand that didn’t go far, and wasn’t in an ocean
environment.
e. The composition of the Uluru arkose is about 50% feldspar (largely Kspar) and 25-35% quartz. (show one). This composition is very
similar to granite and granite-like rocks. (show).
f. There are rocks of these compositions in mountain ranges to the
south and west of uluru. These rocks have ages of 1-1.5 billion years
ago, but about 550 million years ago these rocks got thrust up in a
plate collision (Petermann orogeny), as Australia was assembling.
g. As the mountains eroded  alluvial fans (define; show picture). Uluru
and Kata Tjuta are made from these alluvial fans, at least 2.5 km thick.
Remember – no trees or grasses at this time, so rocks were exposed
and eroded quickly. Uluru and Kata Tjuta were formed from the
eroded sediments of different starting rocks, so they have slightly
different compositions – Kata Tjuta is made from coarser gravel that
was compressed to form conglomerates.
h. By 500 Ma, the area was flooded by a shallow sea (as were much of
the world’s continents), and marine much and sand were deposited
on top of the alluvial fan sands, compacting them and turning them
into rock (the arkose sandstone).
i. Seas receded during 400-300 million years, and a second mountain
building event, the Alice Springs Orogeny, occurred, which tilted the
rocks a great deal in the region of Uluru (85deg), but only a little bit at
Kata Tjuta (15-20deg). From this time onward, the rocks have been
eroding away.
j. By the end of the Cretaceous, 65 million years ago, a valley between
Uluru and Kata Tjuta was being filled in by river sediments.
5. One very important aspect of Uluru --- wonderful example of how some of
these geologic wonders are considered to be sacred objects, revered for
religious or spiritual significance as well as their beauty or spectacular
appearance.
a. Many, if not all, of the geologic wonders I am discussing are part of the
cultural myths of the native peoples who have long lived there.
i. Often part of creation stories; tell us something about the early
peoples who lived there.
ii. Often anthropomorphized. Ex/ in last lecture (Bryce), the
Paiute natives in the area believed that hoodoos were the
people of ancient tribes whom the trickster Coyote turned to
stone.
b. Uluru figures prominently in the Aboriginal Dreamtime, to the point
that climbing Uluru is strongly discouraged because it crosses a
prominent Dreamtime track.
i. Explain the Dreamtime – calling forth the world into physical
existence from the spiritual world where we always have and
will exist. 'The Dreaming' is not a creation myth, per se, but a
myth of formation. The world existed, but was featureless.
Giant semi-human beings, resembling plants or animals, rose
up from the plains where they had been slumbering for
countless ages.
ii. These ancient heroes roamed the land aimlessly. As they
wandered around, they carried out the tasks that the present
Aborigines do today including camping, making fires, digging
for water, fighting each other, and performing ceremonies.
When the heroes became tired of doing these things,
Dreamtime came to an end.
iii. Wherever the creators had been active, some form of natural
feature now marks the place. The creators made everything
with which the aborigines are in daily contact and from which
they gain their living. The heroes also established laws that
govern all aspects, both secular and sacred, of the tribes.
iv. Dreamtime was in the past, but it is the Aborigines present
religion and culture. The saying, 'As it was done in the
Dreamtime, so it must be done today,' dominates all aspects of
aboriginal behavior. Because of their beliefs in 'the dreaming,'
ceremonies and rituals are held, stories are told, pictures are
drawn, and daily life is defined.
v. One story tells of serpent beings who waged many wars
around Uluru, scarring the rock. Another tells of two tribes of
ancestral spirits who were invited to a feast, but were
distracted by the beautiful Sleepy Lizard Women and did not
show up. In response, the angry hosts sang evil into a mud
sculpture that came to life as the dingo. There followed a great
battle, which ended in the deaths of the leaders of both tribes.
The earth itself rose up in grief at the bloodshed, becoming
Uluru.
6. There are many other fascinating geological wonders in Australia that have
formed from the weathering of the old rock there.
a. Mt. Connor
b. The Bungle Bungles
c. The Pinnacles (Nambung National Park)
d. Wave Rock
7. Top 5:
a. Roraima (Venezuela) – huge table rock, featured in the animated
movie “Up.” Was the inspiration for Arthur Conan Doyle’s “The Lost
World”
b. Table Mountain (Cape Town, South Africa)
c. Sigiriya (Sri Lanka)
d. Sugarloaf Mountain (Rio de Janiero, Brazil)
Questions:
1) What is the difference between how a feature like Uluru forms and how karst
towers form?
2) Uluru and Kata Tjuta sit in the middle of a desert. What do you think they
would look like if they were in a tropical region?