#BucketListOdyssey #1 Walk in a Meteorite Crater

The Tswaing Meteorite Crater

2 old friends

a producer & a paramedic

defying menopause

on a Bucket List Odyssey

Old friends Vanessa Yelseth and Kim Williams travel across South Africa bringing you affordable bucket list adventures

#bucketlistodyssey :

#1 Visit a meteorite crater

Tswaing crater / Pretoria crater / Pretoria salt pan

Date: Saturday 26th September 2015

Place: Pretoria Gates open: 07h30 – 16h00

Entrance Fee: R20 Adults R10 Kids

Hike: easy 7.2 km will take about 3 hours

Tswaing Crater

We are super excited to take you along on our Bucket list adventure today. We are actually going to visit a place where a rare and extraordinary event took place some 220 000 years ago. This little gem is not a very well-known place and seems to have remained a bit of a secret. We are hoping after today to change that as this a really very special place and I really think it should be on every schools outing list

So what is this place?

Well we are off to explore a real meteorite impact crater. Yes we do have one of these in our back yard right here in the Pretoria Highveld, South Africa.

Located about 40km (25mi) northwest of Pretoria, Tswaing is a 2 000ha conservation area that is home to a meteorite impact crater and surrounding wetland, as well as the remains of an old salt factory which we will show you a little later and explain some of its interesting history. It is a very popular place among birding enthusiasts.

What is so special about this place?

It is one of the world’s best preserved meteorite craters and it is also very accessible for anyone to come and explore this gem in all its magnificent wonder! It also one of World’s most visible impact site which also happens to be one of the few craters that you can actually walk down into and explore its bottom floor. Today the crater is contained within a 2 000ha nature reserve focused on the preservation of the natural and cultural heritage of this site. The reserve consists of several habitats, an extensive and rare wetland, Savannah, forest, riverine bush and its own ecosystem and mini-delta harboring many streams and islands all centered on the salt lake which is 13 times saltier than the Dead Sea according to Deputy Director of Ditsong Tswaing Meteorite Crater.

Just east of the crater is the Soutpanspruit, a spring which feeds the rare wetland system. The salt lake found in the center of the crater is also a rare occurrence. What is also unusual is that this crater was formed by a stony meteorite rather than the an iron meteorite which often gives rise to the smaller known craters. The Tswaing crater is also on the tentative list for consideration as a World Heritage Site. So let's keep our fingers crossed!

Are there other craters in South African and Africa

This crater, formerly known as the Pretoria Saltpan (or Zoutpan), is one of about 170 impact craters in the world and one of four known impact craters in South Africa.

South Africa, Free State Province, is also home to our own huge 2 000 million year old impact structure at Vredefort. Also known as the Vredefort Dome, which is found 100km SW of Johannesburg. This huge dome was created by the rebound from the actual impact and is a colossal some 250-300 km wide. This is actually the oldest and largest impact structure known on Earth and was declared a UNESCO world heritage site in 2005! This is another bucket list adventure we will be bringing to you!

Others impact craters in South Africa are Kalkkop crater found in the Karoo, in our Eastern Cape Province. The impact site of this meteor that hit earth around 250 000 years ago left a crater 460m in diameter and more than 200m deep. Morokweng Crater is located in the Kalahari area of our North West province and was formed around 145 million years ago. It is estimated to be 70km in diameter. Morokweng is not visible form the Earth’s surface and it was only recently discovered in 1994 while work was been done during magnetic and gravimetric surveys.

We found a further 19 confirmed impact craters and 4 unconfirmed craters scattered around the African continent. The 4 unconfirmed craters are referred to as such because they are not yet listed on the Earth Impact Database due to some rather stringent requirements regarding evidence and peer-reviewed publications, therefore newly discovered craters or those with difficulty around collecting evidence generally are known to scientists for some time before becoming officially listed.

Right so back to today’s bucket list adventure The Tswaing Crater!

Tswaing, which means “place of salt” in Setswana, is the site where a meteorite the size of half a football field slammed into the Earth 220 000 years ago, forming this crater which is 1.4km in diameter and 200m (660ft) deep. It would probably have taken no more than 10 seconds for the meteorite to slam into the ground after entering the atmosphere.

In geological terms, the Tswaing Crater represents one of the youngest and best preserved small bowl-shaped meteorite impact craters in the world. The crater is known, both nationally and internationally, as the Pretoria Saltpan (or Zoutpan Crater).

The meteor that hit here would have been around 30 – 50m wide. The actual circular rim of the crater that you see here rises to an impressive 100m in height. The hills we see when we look up at the rim are the original walls of the impact crater left by the asteroid which hit and it was originally about twice as high as we find them today. Inside the crater we find the rare salt lake 100m in diameter and some 3m or so deep. Therefore it is actually fairly shallow. The crater is very humid and an eerie silence is in the air. Very little if any wind seems to reach down into the crater and cool things off. It appears that the remaining walls of the crater rim keep the wind at bay.

So what made the crater?

“A scientific dispute was ongoing regarding the origin of the carter between supporters of volcanic origin (Wager, 1922) and those who believed it to be an impact crater (Rohleder, 1933) until 1990 when examination of the core from a borehole proved that it is an impact crater. - Eugene Merle Shoemaker showed that craters like this one were formed by impact.”

Drilling in the crater showed that the rocks forming the crater would have been shocked by an explosion and is not of volcanic origin as previously believed. In 1990 with the application of high-power microscopes, the experts found just what they were looking for: evidence of the extraordinary temperatures and pressures of shock metamorphism. Minute spherical particles of glass, formed at the time of impact, were found in rock core drilled from the sandy fragmental breccia. Core samples from deeper within the boreholes showed equally diagnostic microscopic deformations features. Thanks to the expertise of impact specialist Professor Uwe Reimold, the mystery had been solved and the carter identified as that caused by a meteorite. Fission-track age dating showed the glass is some 220 000 year old and as such gives us the estimated date of the impact.

In the explosion that created the crater, the incoming object would have been largely vaporized and scientists have found no large object buried in or under the crater. At the point of impact all life forms within the immediate area and some 3-4 km around the crater, as well as the rock would have vaporized together with the meteorite. An area of 1 000 square kilometers would have been completely flattened and the huge air blast of around 1 000km per hour that followed would have added to their destruction

How Big was the Bang?

The explosion that occurred on impact was caused by the rapid release of kinetic energy (energy due to its motion) of the object as it comes to a stop in about one hundredth of a second. The impact speed of an object falling from rest in space onto the earth is 40 000 km per hour. Incoming objects would not have been at rest and typically impact with a speed of around 60 000km an hour, therefore around 16km per second.

The kinetic energy released when an object travelling at this speed is brought to rest in the impact is 100 joules per kilogram of mass. This is 25 times greater than the energy produced by the detonation of the same mass of high explosives such as TNT. Therefore 100 atomic bombs and 100x more powerful than the Hiroshima atomic bomb blast. The stony projectile some 30-50m in diameter was vaporized by the blast which excavated a crater more than 100 m deep and over a kilometer in diameter. Bedrock from near the impact would have been ejected and overturned and flung out to a distance of several hundred metres.

How big was the object?

From the amount of energy released scientists are able to calculate that the mass of the object must have been around 300 000 tons. That is huge and to put it into perspective the average male bull elephant weights up to 6 tons, which would mean a total of 50 000 male elephants would be needed to make up the 300 000 tons.

How did the salt lake form?

A spring gave rise to this lake and rainwater is also collected within its bowl. We are now left with a spectacular natural wonder with this special salt lake at its heart. Remember that all water in the environment has some salt in it. Salt lakes form when the water containing salt or minerals flow into the lake and cannot leave because the lake is endorheic (terminal). The name endorheic is Ancient Greek word meaning “within” and is a closed drainage basin that retains water and allows no outflow to other external bodies (like rivers and oceans) converging instead into lakes and swamps. This landlocked body of water then evaporates; leaving behind any dissolved salts and this increases its salinity making a salt lake an excellent place for salt production.

Oceans are salty because no water flows out of it. The water can evaporate and fall again somewhere else as rain, but the salts stay behind, over time the salts build up and are eventually left at the bottom of the ocean. And this same principle applies to how inland lakes become salty.

High salinity will also lead to unique halophilic flora and fauna (halophiles are organisms that thrive in high salt concentrations) and even an absence of life near the salt lake. Over time carbonate and sodium chloride salts will have accumulated resulting in Tswaing Lake becoming hypersaline with a pH around 10. When a salt lake is termed hypersaline is means it contains 50% or more salt content. Fresh water has less than 0.5% salinity.

It is interesting to note that there are only 2 ways in which an inland salt lake can from: interior force and exterior force. The interior movement of the Earth, especially the crustal movement contributes to the interior force, the force forming by the environment of the Earth surface results in the exterior force.

When we discuss the Morphology of the crater we find that….
The outer rim is composed of shattered rock called breccia and is elevated above the surrounded plains. Most of the original ejecta blanket has been eroded away but many large granitic blocks can still be found even up to hundreds of meters way from the crater rim.

If we look at the Geology of Tswaing we find that…..

Igneous Rocks: the most common rock type at the crater and in the surrounding region is the Nebo Granite. The Nebo Granite is part of the Bushveld Complex – a large layered igneous intrusion. The Bushveld itself is a geological novelty, consisting of several vertical kilometers of layer magmatic rock which extends horizontally for several hundred km. The 2.06 million year old Bushveld Complex is also one of the world’s largest sources of platinum group metals.

Various small intrusion and dykes also cut into the granitic rock that formed the crater rim. These small intrusions are much older that the crater (1.3 billion years old)

What was the Projectile made of: unlike other small impact craters the Tswaing projectile is believed to be chondritic (stony meteorite) in its composition. Other small impact craters are all associated with iron projectiles.

Breccia and impact generated rocks: a sandy breccia layer, sampled in a drill core of the crater contains an abundance of shock-metamorphosed quartz and feldspar grains, in addition to melt and glass fragments. This type of impact generated rock, known as suevite which simply put is rock that consists party of melted material, typically forming a breccia containing glass and crystal or lithic fragments formed during an impact events.

Sedimentary Rocks: an important group of regional sedimentary rock units known as the Karoo Supergroups is found near the crater. These rocks were thought to cover the granite in the local vicinity during the time of the impact. The sediments which formed these rocks were deposited 220 million years ago during the Triassic, Karoo sedimentary rocks consists of shale, sandstone and gritty sediment.

Lacustrine Sediments: the center of the crater floor is covered with a hyper-saline lake. The highly salinity of this lake made it a source for the commercial extraction of soda brine from 1912 to 1956. At various times in the past this lake has deposited carbonate mud, limestone and evaporates on the crater floor to a current depth of nearly 90m

Why the changing colours of the lake?

The lake varies in colour from a breathtaking blue to greyish and acid greens depending on the rains and seasons. A constant film of “bubbles”, which seem to sit on the surface add to its quiet eerie disposition. During the rainy season it will lean towards an acid green in colour and the growing algae will add drama to the intensity of colour. During the dry months it turns dark the colour of Coca-Cola and has to wonder what lurks beneath its dark surface!

What was it like before the impact and what lived here?

As we highlighted earlier, Tswaing was originally thought to be a volcano but in 1989-1990 boreholes were drilled into the crater floor, hitting solid granite at 200m. Analysis of quartz grains showered that there was shatter cones and recrystallized glass fragments, typical of an impact confirming its origins as the remains of the meteorite impact.

Also revealed where the climatic conditions going back 200 000 years. Unlike the present climate of sub-tropical and dry humid conditions, in the past there were alternating dry and wet periods and at one point the site was a forest of yellowwood trees. These drill sites now contribute to the water flow into the lake and are still visible in the form of pipes producing from it.

The analysis revealed too what animals now extinct lived at the time of the impact. These include the giant wildebeest or hartebeest, a long horned giant buffalo and a giant zebra.

The ecosystems of the Tswaing meteorite Crater Lake are unique because the biological diversity and community structure is governed primarily by salinity and the degree of environmental stability. Lake Tswaing receives very variable annual rainfall which in some years might be above the average regional annual rainfall. However today only algae and one species of salt tolerant plants survive in this salty water

Lake deposits have recorded the climate history of the last 190 000 research on this valuable scientific asset continues.

What animals are round here now?

The Tswaing Crater is covered in dense bush with an abundance of wildlife. Just east of the crater is the Soutpanspruit, which feeds a rare and extensive wetland system with a mini delta that is home to game, a large number of bird species, smaller mammals such as otters, genets, brown hyenas, civets and steenbok, reptiles and various frogs. This mini delta harbouring many streams and islands which attracts up to 250 recorded bird species such as the African hawk eagle, the river warbler, bee eaters and kingfishers. Game is abundant and we can find kudu, impala, zebra, warthog mongoose snakes and leguaans or monitor lizards.

What plants grow here now?

Up to 480 plant species have been record in two rare habitats in an around the lake and crater. The vegetation around the crater is classified as mixed and halophilic archaea, algae and bacteria live in the salt lake.

The Sickle bush is one of the major native encroaches in the bushveld. It quickly colonizes disturbed areas particularly those that have been overgrazed or previously cultivated. This tree has a competitive advantage over other indigenous species because it can grow in all soil types, it coppices readily from any small piece of the root and the seeds are not digest when they get eaten. The seeds pass out of an animals gut untouched and are deposited in ready made pile of compost. The flowers of the sickle bush are the most unique and striking of the bushveld flowers. The flowers look like miniature Chinese lanterns and sometimes it’s referred to as the Chinese lantern tree. It flowers of the Christmas season. The inner bark can be used to make a very strong, reliable rope. The rope or twine is traditionally used to facilitate the healing of scorpion stings and snakebites. The chewed root or leaves is applied to a scorpion sting or snakebite and then bound onto the wound with the twine from the tree. The same treatment can be given to irritating insect bites.

The bark has long fissures. By powdering the bark skin conditions of various kinds can be treated. The inner bark is used to treat toothache and stomach complaints. The sickle bush is really the A-Z of medicinal plants- it has antibiotic properties and used very successfully for numerous conditions like pneumonia, abscesses, dysentery, gonorrhea and intestinal worms. This hard wood is great for the use of handles for tools. Also the wood is termite resistant and long lasting.

The clusters of contorted pods are eaten by animals for their high nutritional value. Eyewash can be made from an infusion of the seedpod to relieve eye irritants. And it’s often grown in the vicinity of homes to ward off evil sprites and charms from the tree are also kept for the same purpose.

Buffalo-thorn is also implicated in a burial ritual. If a man dies away from home, a friend or family member will travel to where he died taking with them a branch for the buffalo-thorn to represent the soul they are going to fetch. During their journey they will buy two of everything – 2 bus tickets – 2 meals – one for the traveler and one for the departed soul. Once the body has been retrieved it will be buried with the buffalo-thorn twig. If there is no body to retrieve the twig alone will be buried to represent the body. In this manner the should is returned to its native land. The hooked thorn is said to have captured the soul and the straight thorn directs it to t heaven sometimes buffalo-thorns are planted on graves to project them from animals.

A poultice of chewed leaves is applied to skin sores. A poultice of the powered and baked roots is applied to any area o pain. It is believed to enhance the treatment if the patient eats the poultice after topical application. The stunning shiny green leaves (responsible for the trees Afrikaans name “blinkblaar wag-n-bietjie” meaning shiny leaf wait-a-while) are edible directly off the tree much like a salad herb or cooked up into nutritious spinach. Giraffe favour the tree as well as many other browsers use it for its nutritious leaves. The fruit ripen into red berries and can be eaten by humans if the birds and monkey have left any behind. These can also be collected, dried and cooked into porridge. The seeds inside are ground up and used as a coffee substitute. The buffalo-thorn is one of the most useful trees in the bushveld and practically very part can be eaten or used to some advantage.

It is considered bad luck to cut a buffalo thorn down after the first rains and drought is sure to ensure. The roots have been used rather successfully in the treatment of diarrhea and dysentery probably due to its high tannin content. It is believed that the tree will protect you from lightening should they take shelter underneath it during a storm. This is possibly because lightning tends to trike the tallest trees in a landscape and the buffalo thorns are typically shorter trees. Please don’t test this belief!! The tree is a source of many cultural beliefs. The Zulu people call this the “tree of life” and liken its zigzag branches with one’s passage through life. At each zigzag junction there is a pair of thorns one hooked and one straight. The Zulus believe that at every junction in life we need to make decisions and the straight thorn resembled the future and looking ahead while the curled thorn cautions us to remember our past. Whatever you would like to believe both of these trees are pretty damn awesome wouldn’t you say?

The arrival of humans

The first visitors to the site arrived during Middle Stone Age times, 150 000 to 30 000 years ago. Small nomadic groups came to Tswaing to hunt game, gather edible and medicinal plants and to collect salt.

Around 800 years ago Iron Age people arrived. Their artifacts such as decorated clay pots and tools have been found on the crater floor indicating the presence of early Sotho or Tswana peoples. The Tswana and Sotho people harvested the salt by filtering and decoction between 1200 and 1800. This was their main reason for being here. The salt was used for preserving and flavoring food and for trade. It is interesting to note that only the women were allowed to collect the salt. To keep the children away and prevent pollution of this precious resource stories about this huge serpent living beneath the water was told.

People subsequently settled in the area farming cattle, crops and collecting salt for domestic use. The cattle farms did not thrive and there were several failed attempts at this mode of farming. When colonists reached the area they named it Zoutpan (Africans for salt pan) and settled, also farming in the area.

In 1912 a soda mine was established in the crater and it operated until 1956. The company called SA Alkali LTD would pump brine from the floor of the crater in order to extract the soda and salt. The lake once contained high concentrations of salt and soda ash that were mined for some 44 years and the remains of the factory still stand near the lake with its many buildings now in ruins.

After several grazing research projects in the area, in 1993 the department of agriculture took over a portion of the farm Zoutpan, and developed it into an ecotourism destination for environmental education, recreation and research

Myth and legend…

The lake is subject of several local legends, including a legend about a monstrous water snake that lives beneath the waters.

Local communities see the site as having huge religious importance. Sangoma’s or diviners are trained here at night. There is still a strong belief that a snake lurks within the lake and when you sit quietly watching the surface of the lake and look up at the rim you can’t help but feel that perhaps something is indeed in there or at least out there!. The footpath around the crater has some steep paths which are lined with sickle bush and buffalo thorns and we are told that a branch of these can be used to collect a wondering spirit and return them to their ancestral home.

As you walk around you will find many stubs of burnt out white candles and small burnt offerings and decorated clay pots all dotted around the lake’s shore and up the sides of the rim walls. This place is considered holy to many. For them the crater was caused by a star that fell from space - from the heavens. Many will come to take water from the lake to use in rituals and others collect the stones which are then heated. Water is then poured over to create steam which is believed to purify believers from sins.

We have also been told that goats and chickens are also sacrificed here. We have found several yellow and black snuff boxes and apparently snuff and beer are poured onto the round to ask for rain, why because this is the place where the ancestors will listen. Groups of Zionists will come along and sing from sunset to sunrise.

What is been done to persevere this wonder of nature for future generations to enjoy?

This is a sensitive and unique conservation area and needs careful management of its multiple cultural and natural resources, in the disciplines of geology, the environmental sciences, biology, and human history. Tswaing is currently being developed by the National Cultural History Museum. This museum places strong emphasis on the protection and use of the area's heritage for purposes if research, education, recreation and community empowerment. All this is done in close consultation with local people, scientists and conservation-oriented institutions. Sadly the museum was burnt to the ground during a runaway bush fire in 2009 and has to be rebuilt. This Meteorite crater museum is one of only 4 in the world.

Visitors are encouraged to take the 7.2km Tswaing Crater Trail, one of three trails that lead to and from the crater rim, and peruse the museum display once its back on track. Several other trails leading to the wetland and delta area are on the cards..

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Photo Credits: Kim Williams Copyright

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