The Earth Story

Life in a sinkhole The karst landscapes of China have been an essential part of their figurative art and painting since time immemorial, capturing the imagination and providing a sense of wonder at nature. The sinkholes here form when underground rivers carve out underground channels by chemical erosion whose roofs later collapse when they weaken. These windows allow sunlight to pour within, and extensive and unique ecosystems to develop underground. Loz Image credit: Song Wen/Barcroft Media http://on.wsj.com/1SdIVxD

Sinkhole Hazard on Missouri Golf Course

Forget the water hazard; this golf course in Branson, Missouri formed a slightly larger hazard; a sinkhole.

Sinkholes are not unusual in the area. Branson is located in an area with karst topography – meaning the bedrock can dissolve in water. Specifically, it is located in the Salem Plateau region of the Ozarks, an area with limestone, dolostone, and sandstone bedrock.

This particular sinkhole is 25 meters (80 feet) wide and as much as 11 meters (35 feet) deep. Many sinkholes form connected to larger cave systems, as caves are produced by the same dissolution that forms these sinkholes.

Not sure what karst topography is? Check out our previous post: http://on.fb.me/1F2TycK

Photo Credit: Nate Papes, Springfield News-Leader

References: http://bit.ly/1dr1ZZz http://bit.ly/1fPdeVR http://bit.ly/1HBMoTC

Cerro Sarisariñama Located in the remote Venezuelan wilderness, hundreds of miles removed from the closest roads, is a Tepui, or a tabletop mountain. This mountain is home to a vast array of plant and animal species, but is renowned among the scientific community for its four giant sinkholes. The largest of these sinkholes, called Sima Humboldt, is over 350 meters wide and 315 meters deep. It is suspected that the sinkholes were shaped over time by the erosional forces of groundwater as it percolated downwards. KKS Read more: http://bit.ly/1HMLLoC http://bit.ly/1D8Ij2d Photo courtesy of Robert Harding and Atlas Obscura

Crveno Jerezo

Can you believe that the sinkhole you see in this picture is 522m deep? The cliff have a height of 241m and the intensely blue lake is about 280m deep. In 1942 one of the cliff walls collapsed after an earthquake. No place to have a swim! (The water is also very cold at 10 °C)

Crveno Jezero (Croatian for Red Lake due to its red cliffs) is the third deepest sinkhole on the planet. You actually cannot even see the immenseness of this sinkhole in a photo. Standing at the edge will make you feel incredibly small and a bit dizzy.

What is even scarier is that at the bottom of the sinkhole the cave extends down even further. Speleologists have not yet been able to determine how deep it goes down due to a very powerful undercurrent in the lake at about 170m depth, which leads scientists to believe that the sinkhole is connected to other watersystems. The presence of a rare species of fish in the sinkhole further fuels this hypothesis. The species: delminichthys adspersus, can occasionally be seen in surrounding rivers and springs in dry seasons suggesting that the sinkhole is connected to the spring and rivers. Delminichthys adspersus are only found in the Dinaric Alps.

The Dinaric Alps are known for its many its karstic formations, the upper Creteceous limestone has formed over 20 large holes that were formed by underground rivers. Due to its near vertical walls, Red Lake is believed to be the youngest of this group. Nearby Modro Jerezo (Blue Lake) is a little bit less deep at 220 m. The earthquake of 1942 caused a landfall and reduced the depth of the lake considerably.

One last scary fact, can you believe that people actually basejump into this gaping hole? Watch a video here (in Croatian):https://www.youtube.com/watch?v=cZIm0BVZ0qI

-OW-

Image: Copyright Barbara Oosterwijk. Crveno Jerezo as seen from above.

References: See here for a cross-section of the sinkhole: https://www.wondermondo.com/crveno-jezero-red-lake/

The "Dying" Sea?

The Dead Sea is a hypersaline lake with a salinity level of 33.7% that borders Jordan, Israel and the West Bank and covers an area of ~600 km2 (230 sq mi). Hypersaline means that it has an unusually high concentration of salts (sodium chloride and others) and has a higher salinity than the ocean (3.5% salinity). While the Dead Sea is not the saltiest lake in the world - that honour belongs to the Don Juan Pond in Antarctica - it is the deepest, with a maximum depth of 307 m (997 ft) below the surface. The lake is also Earth's lowest point on land with the lake's surface at an elevation of 429 m (1,407 ft) below sea level.

The name “Dead Sea” refers to the fact that most life forms (with the exception of some bacteria and microscopic algae) cannot survive in its waters. However, the lake has drawn interest from medical researchers who are using the unique chemical and physical properties of its mud and water to treat number of health conditions including psoriasis (a chronic skin condition) and osteoarthritis of the knees.

Sadly, the Dead Sea may be dying. Due to water diversion from the Jordan River which normally flows in from the north (visible as a thin line at the top of the image), the level of the lake (as well as the undelying groundwater) has dropped significantly. The image I've included shows the drop in water level since 1972. At the southern end of the lake you can see the mineral evaporation ponds from which carnalite (potassium magnesium chloride) is harvested.

As a result, sinkholes (up to 1 per day) have begun forming in the area as briny groundwater is flushed out by freshwater. The freshwater then dissolves away the rock, forming caves. that grow larger and collapse, causing sinkholes and an elaborate underground drainage system. This link (https://bit.ly/2JpuXgh) describes the causes and consequences of the Dead Sea decline.

Past articles: Extreme environments - http://on.fb.me/1vEdUEm

Image credit: NASA image by Robert Simmon, using Landsat data from the United States Geological Survey. Caption by Aries Keck and Mike Carlowicz. (http://visibleearth.nasa.gov/view.php?id=77592). I recommend checking out this link as it describes the colouration of the image and a bit about the cultural significance of the Dead Sea. Further reading: More on the Dead Sea - The chemistry and biology of the Dead Sea -http://bit.ly/1D4DevS More on the Lisan karst system - http://bit.ly/1Bqjzmk(requires login via your local library)

Childhood memory

When I visited Fontaine de Vaucluse in Southern France as a kid, the idea of a bottomless spring frightened me in such a way that I could not sleep. When I found out that people had actually been trying to dive down into it and failed to find the bottom I decided I never wanted to swim anywhere ever again. However, as years passed by this fear gradually moved on to become a fascination for deep sinkholes, caves, lakes and oceans.

Nevertheless, I am still not too keen on swimming in any of those (ever). As of course it turned out (my dad probably tried to scare me even more by saying it was bottomless) the depth of Fontaine de Vaucluse with its beautifully turquoise water was known. Divers have reached depths of 205m, in the process finding large amounts of offerings (mostly coins from the Roman period). Throwing coins into this sinkhole is a tradition that still continues today.

Since it was too deep for humans to dive in, robots eventually determined its depth at 308m, however the robot that reached that depth took a picture on the bottom of the well, revealing a horizontal cavern moving away from that spot.

OW- Image: Cedric Puisney. The well of Vaucluse in summer when water levels are low. See here for scheme of how deep (and narrow) the spring actually is:http://www.wondermondo.com/Countries/E/France/Provence/VaucluseSpring.htm

The Bayou Corne sinkhole

This image shows a man-made disaster in the state of Louisiana known as the Bayou Corne sinkhole. The sinkhole formed when the surface collapsed on August 3rd, 2012 following a series of small earthquakes, and rapidly filled in with groundwater.

This sinkhole is the subject of new research published in the journal “Geology” that describes interesting processes occurring before the sinkhole opened that could have implications for future sinkholes.

The sinkhole is located on top of a mine which was extracting salt from the underlying Napoleonville salt dome by pumping water in, dissolving the salt, and pumping out the brine. This process formed a large gap in the salt dome which collapsed, forming a mile-deep cave and releasing a variety of gases including methane and hydrogen sulfide from a nearby natural oil reservoir into the air. Several hundred local residents were evacuated, Louisiana declared a state of emergency, and to this day most of the residents have been unable to return to their homes.

Residents of the area were complaining of ground motions in the months before the collapse. Using satellite data including images and radar, scientists at the Jet Propulsion laboratory and US Geological survey have reconstructed parts of what happened before the collapse.

No deformation was seen prior to June of 2011, but for about a year beforehand, the ground started subtly shifting. In total, 26 centimeters of sideways motion were detected right above the location where the sinkhole formed in the year prior to collapse. The ground itself creaked and slid as the support underneath weakened.

The earthquake swarm started in June of 2012, slightly after ground motion began. Thus, this sinkhole gave a long warning period before it formed. If this technique can be generalized, similar ground motions might give a warning before large sinkholes form in other populated areas.

A variety of lawsuits are pending against the companies that operated the mines. The sinkhole continues growing today, and is now threatening nearby highway 70.

-JBB

Image credit: http://www.flickr.com/photos/assumptionoep/7832115946

AGU abstract: http://www.sciencecodex.com/new_geology_research_explores_intriguing_questions-125145 http://m.livescience.com/42103-radar-catches-bayou-corne-sinkhole-form.html?cmpid=514645

Melissani Cave, Kefalonia, Greece - open to both the air via a skylight or sinkhole and to the sea for boats.

The Sunken Garden

The city of Mount Gambier in South Australia is located on the slopes of a volcano comprising several craters. Volcanic craters, however, are not the only ones found in this area. A number of sinkholes can be seen throughout town created by collapsing limestone caves. Weakly acidic groundwater moving down joints and along cracks and bedding planes slowly dissolved the limestone and created a series of caves. Eventually, the roofs of these caves collapsed and created sinkholes.

The Umpherston Sinkhole, in particular, was transformed into a beautiful garden about 130 years ago by James Umpherston. When he purchased a farm property and found the collapsed cave he decided to create a relaxing spot for the people of Mount Gambier. The garden became an immediate success and even contained a small lake. After the death of James Umpherston, the garden fell into despair but was rebuilt about 40 years ago.

The Sunken Garden, as it is called, is made up of several terraces planted with tree ferns and hydrangeas. The walls of the sinkhole are garnished with hanging ivy. At night, the floodlit garden becomes a popular gathering point for possums.

Xandi

Image Credits: http://bit.ly/2y7t3r3 http://bit.ly/2xqGV2b Sources: http://bit.ly/2ygNJ0n http://bit.ly/2y6VVzx http://bit.ly/2y7hHTG

Dean's Blue Hole Blue holes are sinkholes or cave systems that were dissolved by rainwater under aerial conditions before being flooded by marine water as sea levels rose at the end of the last ice age. Dean's is located in a bay on the coast of Long Island in the Bahamas and at 202 metres is the deepest marine hole so far discovered. Its outer diameter is 35 metres and widens into a hundred meter cave lower down. We covered the Great Blue Hole of Belize in a previous post at http://tinyurl.com/obce86d Loz Image credit: Ton Ingwirda/Wikimedia Commons http://www.atlasobscura.com/places/deans-blue-hole More wonderful photos: http://ngm.nationalgeographic.com/2010/08/bahamas-caves/skiles-photography

Incredible waterfall, Indonesia

Melissani Cave, Kefalonia, Greece