The Earth Story

Tessellated Pavement in Tasmania

Eaglehawk Neck, located in Southeastern Tasmania, is a narrow isthmus connecting the Tasman Peninsula to mainland Tasmania. The area boasts many natural wonders to observe, from the southern lights to rare geologic formations. The most famous of these geologic formations is the Tessellated Pavement, an area of flat rock that gives off the impression it was molded by human hands. Yet, nature’s ability to create should never be underestimated and at Eaglehawk Neck nature proves it is capable of producing landscapes eerily similar to those made by humans.

Tessellated pavement gets its name from its resemblance to Roman mosaic floors, which are also called tessellated pavement. At Eaglehawk Neck two types of formations can be observed: pan and loaf formations. Pan formations form when saltwater erodes the central surface of a stone block creating shallow pools. This usually happens at a safe distance from the shore, allowing saltwater to crystallize in the concave depressions of the stone. Loaf formations are typically located closer to the shore and are inundated with water for longer periods of time. Water, carrying abrasive sand, is funneled through the joints eroding them faster than the rest of the pavement. Protruding structures resembling loaves are eventually created. The image below is a pan formation.

KKS

Read more: http://bit.ly/1sLm02L http://bit.ly/1HLWWhu

Photo courtesy of JJ Harrison[_

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Great Asby Scar

This remarkable landscape is the Great Asby Scar in England’s Cumbria County. I had trouble believing it at first, but these barren rocks are actually limestones.

Limestones are marine rocks that, in my experience, erode and easily form soils in most climates. Here, however, we have a “limestone pavement” – an area of flat, exposed, weathered limestone rock surfaces. These limestones are carboniferous in age, formed at a time when many areas around the world formed carbon-rich rocks.

The combination of altitude, previous glaciation, and lack of exposed soil surfaces where new plants can grow leave the Scar as a barren, fractured, rocky terrain in Northern England. The fractures you see are joints – parallel sets of fractures that form in rocks as they approach the surface and pressures are relieved. Exposure to the elements allows soil and occasional plants to develop in the low ground between those rocks, while the flat, soil-free surfaces stay unvegetated and desolate.

-JBB

Image credit: https://flic.kr/p/qXMe3a

Read more: http://link.springer.com/article/10.1007%2Fs002540050085

Hoodoo Birth

This photo comes from a location in the state of Utah known as Sidestep canyon. It’s off the beaten path from the major national parks, but one treat of the Western US is that the same features that define national parks like Bryce Canyon can be found in a number of spots. In this location you can see one of Bryce’s most famous features, Hoodoos, being born.

Hoodoos are spires of rock that stand up in desert regions. They form when small amounts of water get into cracks in rocks and force them apart through a combination of erosion and frost wedging – expansion and contraction of water as it freezes adds a force that breaks the hoodoos apart.

The layering in hoodoos reflects the strength of the sedimentary rocks. More easily eroded layers become thinner, while stronger layers hold together and often form caps. Once water breaks through a cap, it can begin separating the rocks into these rough features.

-JBB

Image credit: John Fowler https://www.flickr.com/photos/snowpeak/15686755802/

Read more about hoodoos: http://www.nps.gov/brca/naturescience/hoodoos.htm Sidestep Canyon: http://fridrich.binghamton.edu/Sidestep%20canyon/index.html http://www.thewave.info/UpperWhiteRocksCode/Map.html

Vertical

These are the sandstones of Arches National Park - these vertical segments are eroded by water into the classic arches. The vertical pattern is dominated by erosion along fractures. Fractures called joints often appear in parallel sets; water is able to sneak into the rocks along these vertical cracks, weather the rocks, and erode downwards.  -JBB Image credit: https://www.flickr.com/photos/molas/53876753/ Read more: http://www.utah.com/nationalparks/arches/devils_garden_hike.htm?sv=1 https://www.classzone.com/books/earth_science/terc/content/investigations/es2903/es2903page04.cfm http://www.nps.gov/arch/naturescience/geologicformations.htm

Squeaky Beach

This panorama comes from Wilson’s Promontory National Park on the southern coast of Australia. The rocks in the foreground appear to be rounded boulders, most likely granites that have broken into pieces and are weathering along those fractures called joints.

The beach in the distance is nicknamed “Squeaky beach” because when conditions are right, the sand will actually emit a “squeaky” sound when walked on.

The sand at that beach is described as a very well rounded, well-sorted quartz sand. When the grains are rounded, there are no sharp edges where grains get stuck together to resist movement. The grains are therefore able to slide past each other easily. This helps create a sound in 1 of 2 ways; either the sound comes from the grains themselves slipping past each other or the sound comes from air being squeezed out from the spaces between grains; at present the interviews with scientists who have studied the beach don’t seem to have a precise answer out of these 2 options.

-JBB

Image credit: Hadi Zaher https://www.flickr.com/photos/hazara/15258747170

More: http://www.abc.net.au/catalyst/stories/2601532.htm http://parkweb.vic.gov.au/explore/parks/wilsons-promontory-national-park/things-to-do/squeaky-beach

Video including the sound and dancing: http://www.dailymotion.com/video/xzlyzu_squeak-squeak-at-squeaky-beach-wilsons-promontory-national-park-oz-2013_travel

Arches without arches

This image comes from Arches National Park, and interestingly, it shows the geologic process that give rise to arches without actually having any arches in it.

The Entrada sandstone in Arches National Park helps give rise to the arches. This sandstone is a strong rock, extremely difficult to erode in the arid environment of the western United States. The only way the rocks erode is along preexisting fractures formed when the rocks were moving up to the surface and the pressure on top of them was removed. Those fractures in this are generally strike either northeast-southwest or northwest-southeast, allowing for linear rock exposures running north-south separated by areas that are more deeply eroded.

In places, the erosion in the fractures penetrates deeply enough to undercut the Entrada sandstone, allowing formation of the arches. In this area, we simply have a lovely shot of a long outcrop of layered sandstone; if erosion pokes through at the bottom of an outcrop like this, the end result would look a lot like an arch.

-JBB

Image credit: Jon Sullivan http://www.public-domain-image.com/nature-landscape/rock-formation/slides/arches-national-park.html

Read more: http://www.nps.gov/arch/naturescience/geologicformations.htm http://geomechanics.geology.pdx.edu/Papers/Pattern/pattern.html

Native silver sculpture As the heated waters of the deep earth forced their way into the spaces in the rock through which they were percolating, they encountered a different chemistry, forcing them to precipitate their cargo of precious metal into the joints of the surrounding gangue. The result resembles something one might see in an ethnographic museum, filled with artefacts from different world cultures, rather than the creation of our wonderful planet that it actually is. The specimen was mined at Batopilas, in the in the Chihuahua province of Mexico in 1968, and measures 5.1 x 3.5 x 3.2 cm . Loz Image credit: Joe Budd/Rob Lavinsky/iRocks.com

Haytor rocks

This lovely image illustrates a geologic feature in southwest England known as the Haytor rocks.

The rocks are granites, produced almost 300 million years ago as the ocean that preceded the Atlantic was closing and North America and Europe collided.

The processes of continental collision and mountain building produced magma within the Earth’s upper crust. That magma rose up and interacted with the sedimentary rocks above, taking some of the chemical elements that are common in sediments like potassium. These magmas eventually formed potassium-rich granites in this area.

The shape of the rocks you see is a result of fracturing. The vertical fractures in the granite likely formed as the magma was first cooling down; rocks shrink when they cool and that shrinking is enough to cause rocks to crack. The geologists term for cracks like that is “joints”.

The horizontal cracks likely formed much later. They are formed parallel to the Earth’s surface, implying that they are related to removal of weight above this granite. As rocks above this level were eroded, the weight and the pressure on the rocks decreased. The rocks were used to being under pressure, so when the pressure was removed, they cracked and expanded upwards.

The area shows several different types of granite and has been used for both quarrying and recreation, including rock climbing. Some links refer to a fairly spectacular granite-lined path used to transport granite away from the quarry sites.

-JBB

Image credit: Dave(creative commons) https://www.flickr.com/photos/snaps11/7871758868

Read more: http://www.ipplepen.net/community/south-west_geology/walks/haytor_granite.pdf http://www.ukclimbing.com/logbook/crag.php?id=1141 http://ougs.org/local_geology/article.php?id=64&&branchcode=swe

This spectacular location is the Bastei Bridge over the Elbe River in eastern Germany near the city of Dresden. The rocks are sandstones of the Elbe formation, deposited in waters of a shallow sea during the Cretaceous period. At the time, sea level was much higher than today and oceans covered many of the continents. Rivers brought sand grains pouring into the area that is now central Europe; those sand grains were cemented into strong layers of sandstone. Once the rocks were exposed…they cracked, allowing water into vertical layers. Those spots eroded, but areas that didn’t crack stood strong against erosion, eventually creating this topography. The bridge over the Elbe river was constructed in the mid-1800s out of rocks of the Elbe Sandstone, and today sits within Saxon Switzerland National Park. -JBB Image credit: http://upload.wikimedia.org/wikipedia/commons/4/4a/Basteibrücke_morgens_%28Zuschnitt%29.jpg http://books.google.com/books?id=-TI55urJYyEC&pg=PA201&lpg=PA201&dq=Elbe+sandstone+Geology&source=bl&ots=7SO5J_znXh&sig=dbjtSvM0bwWYX6BM83tMO0o_35c&hl=en&sa=X&ei=zSsJU-LZGc_PkQemrIHgCA&ved=0CFUQ6AEwBQ#v=onepage&q=Elbe%20sandstone%20Geology&f=false

Check out the fracture patterns in this huge pluton - those fractures are called joints and they define how this diorite weathers.

Watson Lake

This is a sunset in part of the Colorado Plateau known as the Granite Dells. Watson Lake was dammed a century ago to create stable water supplies for the nearby city of Prescott and the surrounding areas. The rocks have the characteristic, boulder weathering style of granitic igneous rocks. Granites are tough; the minerals in granites don't easily undergo chemical weathering and because the crystals are large, there isn’t a lot of surface area where water can get in-between grains to force the rock apart. The only place that water gets into a rock like this one is where the rock is already fractured, and usually granites form large fractures called joints every few meters as they approach the surface. Water gets into the rock along these fractures and weathers the rock to large, rounded boulders.

This granite is 1.4 billion years old. It is one of many granites in this part of Arizona; a belt of ancient igneous rocks cross cuts the country and is a remnant of the assembly of this part of the continent. The original continent of Laurentia grew by the growth and addition of several large mountain ranges at this side between 2 and 1 billion years ago; this granite is the remnant of one of them.

-JBB

Image credit: https://flic.kr/p/NSDsvZ

Reference: http://bit.ly/2p32elB http://europepmc.org/abstract/med/2917844