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EarthCache

Port Elizabeth ancient fault lines

A cache by FireflyAfrica Send Message to Owner Message this owner
Hidden : 5/28/2014
In Eastern Cape, South Africa
Difficulty:
2 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:

Port Elizabeth isn't really know for it's earth quakes, but that doesn't mean that it's never happened.  This Earthcache discribes the history of earthquakes in Port Elizabeth and where to look out for signs of it.


There are three ancient fault lines in Port Elizabeth where some slight movements can still occur. One of them, the Moregrove Fault, runs along the Port Elizabeth beachfront from Pollok Beach, Summerstrand, along the shoreline, through the Baakens Valley and ending at the Moregrove quarry near the Kragga Kamma interchange.  Another, the so-called Chelsea- Noordhoek Fault, runs parallel to the Schoenmakerskop coast, while a third fault runs in the Coega area.

 

In some places in the Baakens Valley the quartzite rocks of the Moregrove Fault is visible.  The old sandstones have been heated to such an extent that all the grains interlock, making it a very hard rock. One side of the rock has dropped down relative to the other as a consequence of Pangea breaking up and the formation of the super-continent Gondwana.  Its this drop that has formed the fault.  The water which continually runs across Lower Valley Road, at the sight of this Earth Cache location, near the old PE Tramways building is underground water seeping to the surface through the Moregrove fault.  This fresh water used to flow into the fresh water lagoon that was situated at the mouth of the Baakens River.  The lagoon was filled in at some stage and the river contained in a channel which is only about two meters wide at this point today.  The water now forms a vlei area next to the cliff before flowing over the road and trickeling down to the river.

MOREGROVE FAULT ... Prof Peter Booth of NMMU’s geosciences department points to the quartzite rocks of the Moregrove Fault in the Baakens Valley.

 

Port Elizabeth earthquake history

One of the earliest recorded earthquakes struck at 10.15pm on Tuesday, 21 May 1850.  The shock was not very severe, but “sufficient to alarm the more nervous members of our population and to awaken from their first slumbers those who had retired at a very early hour to rest,” reported the Eastern Province Herald. The earth shook for about a minute and those inside their homes described the shaking as though it was a very violent wind. The newspaper reported that there had never been an earthquake in the young town before.

“The shock was felt most severely towards the north and west ends of the town. It was sufficient in these quarters to move lighter articles, such as glasses, mantle-piece ornaments, etc, from their places,” the Herald reported.

After the earthquake had subsided, most residents went outside to inspect their buildings for damage. The air was very still and a heavy dew had descended. Several people said they had perceived a sulphurous smell during the earthquake. There are reports in Morse Jones’s Lower Albany Chronicle in which it was noted the tremor was also felt in the Lower Albany area and had been violent enough to inspire the local Xhosa community to come up with a special word for it: inyikima.

In January 1900, a quake was felt in the Tsitsikamma area strong enough to dislodge crockery from shelves in some houses. Another tremor was felt in Port Elizabeth in 1912.

On December 4, 1920, a tremor lasting about 20 seconds, the result of a strong earthquake out at sea, was felt in Port Elizabeth, Cape Town and George.

In 1929, an early morning earthquake large enough to cause damage to buildings was felt in Grahamstown. This was followed on August 9, 1932 by a fair-sized tremor felt in Alice, Queenstown and Graaff-Reinet.

There have been several other occasions when Port Elizabeth felt the earth shake.

At 3am on January 12, 1968, a tremor shook the Eastern and Southern Cape and was felt in Port Elizabeth, Uitenhage, Mossel Bay and Graaff-Reinet. It lasted about two minutes and was hard enough in Uitenhage to cause furniture to move and pictures to fall from the walls of homes.

In Joubertina, Leon Olivier, 14, was shaken off his bed. A glass containing false teeth, which was knocked off a table, became a talking point.

On October 3, 1977, a tremor felt at many places in Port Elizabeth between New Brighton, Summerstrand and Seaview, was recorded in Pretoria. It was not to be the last.

The Herald reported that at 8.55pm on Sunday, 6 October 1986, a strong tremor – registered at 4.9 on the Richter scale – “rocked buildings and sent people fleeing from their homes” as it rippled its way through large sections of Natal and the Eastern Cape. The tremor was felt in Port Elizabeth, East London, Aliwal North, Queenstown, Elliot, Mthatha and Durban. A caller to The Herald said it had been violent enough to knock ornaments from a table. On the Port Elizabeth beachfront, residents in Mutualhof (now The Beaches) in Humewood and Marine Towers in Summerstrand reported a severe shaking which “seemed to last a few minutes”. Residents in Swartkops, Greenbushes, North End and Kini Bay all reported feeling the tremor.

Dr Robert Kleywegt, of the Mineral and Energy Affairs Department, said at the time that coastal towns and cities were particularly prone to the effects of minor tremors.

“Along the coast, a lot of high-rise buildings are on poor foundations – piles driven into waterlogged sand.”

It is believed that the tremor’s epicentre was in Lesotho or the north- eastern Cape.

The worst earthquake to hit South Africa struck on September 29, 1969, when nine people were killed in the areas of Tulbagh, Prince Albert, Ceres and Wolseley during a 6.5 magnitude earthquake. Damage, which included many historic buildings in Tulbagh, totalled R20-million.The most recent earthquake occurred two months ago – on December 1 – 10km off the Transkei coast.

South Africa as a whole does not normally get large tremors except in the Witwatersrand where they result from mining activities.

However, there are three ancient fault lines in Port Elizabeth where some slight movements can still occur. One of them, the Moregrove fault, runs along the Port Elizabeth beachfront from Pollok Beach, Summerstrand, along the shoreline, through the Baakens Valley and ending at the Moregrove quarry near the Kragga Kamma interchange. The water which continually runs across Lower Valley Road near the old PE Tramways building is underground water seeping to the surface through the Moregrove fault. Another, the so-called Chelsea- Noordhoek fault, runs parallel to the Schoenmakerskop coast, while a third fault runs in the Coega area.

Dr Steffen Buettner, senior lecturer at Rhodes University, said: “Major seismic activity in the region ... was linked to the break-up of the super- continent Gondwana (about) 150 to 125 million years ago.

“At that time, the Earth’s crust was stretched and extended, forming faults, fractures along of which crustal blocks moved downwards.

“The major tectonic movements came to an end more than 100 million years ago, and what causes occasional tremors nowadays is just an aftermath which is not likely to end up in a significant earthquake.” - Source - The Herald

Along with logging this cache you need to e-mail the answers of the following questions via my profile.

1) Name (or describe) some of the plants you see that grow in the vlei (swampy area) where the water flow out from the fault.

2) Describe the rocks on the cliff

3) Do you think there is a chance of a major earthquake coming to Port Elizabeth and why?

4) Optional - Please take a selfie in the valley and upload it along with your log. It can either have the cliff side or the opposite cliff with Fort Frederick on top in the background.

 

Additional Hints (Decrypt)

Erzrzore gb r-znvy lbhe nafjref

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)



 

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Last Updated: on 9/7/2017 10:56:43 AM Pacific Daylight Time (5:56 PM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum

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