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Geology, Geology Talk

The Vermilion Cliffs National Monument in northern Arizona, US, the perfect place for ‘wave riding’.
The Vermilion Cliffs National Monument in northern Arizona, US, the perfect place for ‘wave riding’.

Surf's up!

Fourteen years ago Bill Langer wrote a series of articles about famous rocks. This month he focuses on another famous rock, recently brought to mind by a daring surfing event …

On 8 November, 2017, the surf was up – way up – when Rodrigo Koxa caught a 24-metre wave off the coast of Nazare, Portugal. Several months later the World Surf League determined it to be the largest wave ever surfed.

If you are reluctant to careen down a gnarly, kick-ass, 24m killer wave, there is an alternative for you – located in the Vermilion Cliffs National Monument in northern Arizona, near the border with Utah.

Vermilion Cliffs National Monument in northern Arizona, US
Vermilion Cliffs National Monument in northern Arizona, US

You’d better be lucky, because the rock formation is so fragile there is a lottery to select who can visit it.

The Wave got its start 200 million years ago during the Jurassic period – the age of the dinosaurs. All of what is now the Colorado Plateau Province, including northern Arizona, was a featureless desert of blowing sand, much like the Sahara Desert of today.

Periodic changes in the prevailing winds during the Jurassic created rhythmic rippled layers of sand as huge dunes migrated across the desert. Eventually these sand dunes were transformed into rocks, one of which is called the Navajo Sandstone.

Erosion slowly nibbled away at the edges of the Colorado Plateau, creating the Vermillion Cliffs. The Wave began to take on its unique shape about two million years ago, when wetter climates brought upon by the ice ages greatly increased erosion in the area. Initially, run-off eroded troughs cut into joints within the Navajo Sandstone.

Eventually, the run-off shrank to the point that it became insufficient to continue cutting the troughs. Wind scour took over, carving the smooth bowl of The Wave. The colour banding and thin ridges seen within The Wave are the result of the different types of minerals used to cement the sand grains together.

If you don’t want to travel to the United States to “rock surf”, you might want to visit another wave near the small town of Hyden, Western Australia, about 350km southeast of Perth.

Wave Rock, near Hyden, WA, got its start about 2.63 billion years ago.
Wave Rock, near Hyden, WA, got its start about 2.63 billion years ago.

Wave Rock, as it is called, is a granite cliff standing 14m high and 110m long. Wave Rock was formed by a multi-stage process of landform development. Unlike its much younger 200-million-year-old American counterpart, Wave Rock got its start about 2.63 billion years ago when a domed mass of magma intruded into the Earth’s mantle near Hyden. The magma cooled to form a medium- to coarse-grained granite plug containing embedded feldspar and other crystals.

The next stage began about 130 million years ago when groundwater flowing through fractures and joints in the granite bedrock chemically altered the hard feldspar crystals into soft kaolin clay. This process formed strongly weathered, loose and disaggregated granite deep underground, right next to solid granite.

About 55 million years ago plate tectonics caused Australia and Antarctica to separate from one another, resulting in the tilting of what became southwestern Australia. Over the intervening years, slow but persistent erosion finally exposed the strongly weathered granite bedrock. The more resistant bedrock remained, while the disaggregated rock and kaolin clay were washed away. This created the concave face of Wave Rock.

The final part of the process began during the last few million years. Rainwater dissolved chemicals from the overlying soil and deposited them as deep grey, red, ochre and sandy brown vertical stripes down the face of the rock. These coloured ribs finish the wave-like appearance of Wave Rock.

So what are you waiting for? Surf’s up!

Bill Langer
Independent Research Geologist

Bill Langer is a freelance writer and retired Senior Research Geologist for the U.S. Geological Survey. Bill is now an independent researcher specialising in aggregate resources. Click here to email Bill or visit his website.
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Thursday, 17 October, 2019 4:35am
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