Tag Archives: geology

The Eye of Africa

3 Apr

The ‘Eye of Africa’ (also known as the Eye of the Sahara) lies within the large east-African country of Mauritania, out in the Sahara Desert. Properly known as the Richat Structure, it is easy to see where its nickname comes from. Looking at it from above, it looks a lot like a big blue eye staring out of the ground. Here’s a picture of the Richat Structure:

Satellite image of the Richat Structure

Satellite image of the Richat Structure

Location of the structure in Mauritania

Location of the structure in Mauritania

Distant satellite image of Mauritania - the structure is still visble

Distant satellite image of Mauritania – the structure is justvisible, even from this far away

It is about 40 kilometers in diameter, and as you can see from the above picture, it is highly visible in satellite pictures.  So, how was this geological wonder formed? Researchers aren’t entirely sure. It was initially thought to have formed as the result of an asteroid impact, but scientists haven’t found any evidence for extraterrestrial involvement, other than its circular appearance.

richat4

Zoomed-in image of the Richat Structure from Google Maps

Geologists now believe that it is most likely to be a very symmetrical ‘geologic dome’. Wikipedia’s summary of a dome is this:

In structural geology, a dome is a deformational feature consisting of symmetrically-dipping anticlines; their general outline on a geologic map is circular or oval. The strata in a dome are upwarped in the center; if the top of a dome is eroded off, the result will be a series of concentric strata that grow progressively older from the outside-in, with the oldest rocks exposed at the center.’

No matter what led to the creation of it, the Richat Structure looks amazing, and I’m hoping that I will get to go and visit it one day.

Doggerland

31 Mar

It’s quite hard to imagine that only a few thousand years ago, there were lands on which people lived that have now completely disappeared into the ocean. But, this is exactly what happened to the area known as ‘Doggerland’.

Up until around 8500-8200 years ago, Doggerland was a large stretch of dry land that linked the European mainland to where the British Isles are today. Here’s a picture to show where it was, compared with what the area looks like today:

This is where Doggerland used to be in Europe. Credit: Max Naylor

This is where Doggerland used to be in Europe. Credit: Max Naylor

The same area today, minus Doggerland

The same area today, minus Doggerland

So, what happened to Doggerland, and how do we know about it?

Archaeologists first started to think that the area may have originally been above sea level in the early 1900’s, when fishing boats in the area would occasionally dredge up the remains of animals that had lived in Europe in prehistoric times, including mammoths and lions (yes, Europe used to have lions!). Plant remains were also brought up and studied by paleobiologists, who found them to be peat from when the land was above sea level and mostly tundra.

To add further interest, prehistoric tools and weapons used by ancient peoples were also found. Archaeologists now believe that Doggerland was occupied by humans during the Mesolithic period (this period started around 10,000 years ago), up until it started to disappear underwater. In fact, some think that it may have been one of the richest hunting and fishing environments available to European humans at the time.

Whilst surveying the area for petroleum, oil-company geologists produced seismic surveys of the land beneath the waves, and in 2012, the Royal Academy of London presented the results of the surveys along with all the artefacts that have been found so far. The seismic surveys allow researchers to see what the land looked like while it was still above sea level, and even Doggerland’s ancient river systems have been mapped in 3D. The largest of these rivers is known as the ‘Shotton River’.

In regards to the disappearance of Doggerland, researchers believe that at the end of the last glacial period, sea levels began to rise dramatically as the climate warmed up. Due to this, Doggerland was eventually submerged under the North Sea, and the British Isles were separated from the European mainland. This probably all happened around 8500 years ago.

Another recent theory claims that after already losing some land to rising sea levels, Doggerland may have become completely submerged as the result of a tsunami that hit the area 8200 years ago. This tsunami was caused by an event known as the ‘Storegga Slide’. It is named this because the event was a massive underwater landslide, occurring off the coast of Norway. The resulting tsunami would have been devastating to Mesolithic people who still lived on Dogger Bank, and after this event, British Mesolithic populations would have been totally separated from the rest.

The yellow numbers represent the height (in meters) of the tsunami waves from the Storegga Slide. Credit: Lamiot

The yellow numbers represent the height (in meters) of the tsunami waves from the Storegga Slide. Credit: Lamiot

One part of Doggerland actually remained for quite a while longer. An island known as ‘Dogger Bank’ emerged when the rest went underwater. Dogger Bank was an upland hill area of the original Doggerland, so the sea levels didn’t rise high enough to cover it. Eventually, however, Dogger Bank also disappeared into the ocean, and this probably happened around 7000 years ago. Here is a map that shows us where Dogger Bank is now:

The red line marks where Dogger Bank used to be. Credit: NASA

The red line marks where Dogger Bank used to be. Credit: NASA

It is fascinating to think that once-populated lands are now totally underwater. Geologists and archaeologists really have the most interesting jobs sometimes!

Wave Rock

26 Mar

There are many well-known natural formations all over the world; The Grand Canyon, Niagara Falls and Mt Everest, to name a few. In Australia, there is a particularly spectacular formation that many of our readers may not be aware of, due to its fairly remote location. I am referring to what is known as ‘Wave Rock’; an enormous rock formation in south-eastern Western Australia, which is the largest state in Australia.

Located 3km (or about 2 miles) from the small town of Hyden, this natural geological formation attracts approximately 140,000 tourists a year. The rock itself is a large granite formation that has been dated to 2.63 billion years old, and was created through complex geological processes. As you can see from the picture below, it closely resembles an ocean wave, hence the name, and is nearly 50 feet (14m) high and 350 feet (110m)  across.

Wave Rock. It stands 14m high and close to 110m long.

Wave Rock. It stands 14m high and close to 110m long.

While there are no creepy mysteries relating to Wave Rock itself, the local indigenous people stayed clear of the area for fear of the spirit ‘Mulka’.

Here is the story of Mulka sourced from the Wave Rock website

Legend of Mulka’s Cave

“The name Mulka comes from an Aboriginal legend associated with the cave. Mulka was the illegal son of a woman who fell in love with a man with whom marriage was forbidden according to their law.

It was believed that as a result of breaking these rules she bore a son with crossed eyes. Even though he grew to be an outstandingly strong man of colossal height, his crossed eyes prevented him from aiming a spear accurately and becoming a successful hunter.

Out of frustration it is said Mulka turned to catching and eating human children, and he became the terror of the district. He lived in Mulka’s cave, where the imprints of his hands can still be seen, much larger and higher than that of an ordinary man.

Apparently, his mother became increasingly concerned about him. When she scolded him for his anti-social behaviour he turned on his own mother and killed her. This disgraced him even further and he fled his cave, heading south.

The Aboriginal people of the area, outraged by Mulka’s behaviour, then tracked down this man who had flouted all the rules. They caught him near Dumbleyung, 156km south west of Hyden, where they speared him to death. Because he did not deserve a proper ritual burial, they left his body to the ants: a grim warning to those who break the law.”

So, how did this formation come to be? As previously stated, the geological processes that led to the formation of Wave Rock are quite complex, but I will attempt to break it down to a simple, easier to understand explanation for our readers. Basically, Wave Rock is a part of a much larger rock known as Hyden Rock, and the shape was created by continuous erosion of the softer rock beneath the upper edge, in the process of weathering. This occurred over many millions of years. Eventually, this resulted in an ‘undercut’ base with a rounded overhanging shape, and ended up in the wave shape that we see today.

Having lived in Western Australia most of my life, I have visited wave rock numerous times. If you ever decide to visit Western Australia, I highly suggest making the effort to go and see the rock and some of the Australian countryside whilst you are there.

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