The Earth Story

The arch at Tianmen Mountain, China

Natural bridges at the Samuel H. Boardman State Scenic Corridor, Oregon

A three tiered chasm

The Bataara (or Ballou Balaa) pothole appears almost out of nowhere on the meadows of the Lebanon Mountain Trail of Tannourine municipality of Lebanon. Three natural bridges, each rising above the other overhang an enormous abyss in which during spring melts a 255m waterfall plunges down into the depths. The waterfall is only observable in March and April. Due to the journey the water has to take to get to the bottom the pothole is also known as Three Bridge Chasm. The pothole was only discovered in 1952 by French bio-speleologist Henri Coiffant and it was not until 30 years later that the cave was fully mapped.

The limestone cave is of Jurassic origin and formed approximately 160 million years ago. Water from a stream slowly seeped into the limestone forming the pothole and the bridges. However, the pothole and the bridges are quite fragile. During winter freezes large chunks of the walls of the pothole fall apart and the pothole is not marked by any signs. Since it appears quite unexpectedly in the landscape one should not get too close to the edges. Potholes are very popular among cavers, however it was decided that due to its instability Batara would not be accessible. A fluorescent dye test in 1988 revealed that the water from the sinkhole emerges at the nearby village of Mgharet al-Ghaouaghir.

Baatara is located on the Lebanon Mountain Trail, a long distance hiking trail of 440km that walks from the north of Lebanon to Marjaayoun. Its main aim is to show the cultural and natural heritage of the Lebanese mountain and bring communities closer together. For more information, see here: http://www.lebanontrail.org/

--BO

Image: Missakasim on panoramio.com. Baatara pothole with the Baatara gorge waterfall. Note the person standing on the second bridge.

References

http://ziadsalloumphotography.com/blog/?p=1790

http://www.kuriositas.com/2011/08/baatara-gorge-waterfall-that-drops-into.html

http://www.lebanontrail.org/

Natural Bridge, Virginia

This towering structure is found in the mountains of western Virginia; the arch stands over 60 meters high and the rock is strong enough to support the weight of a road that now sits on top.

The rocks at this site are Ordovician-aged dolomites, formed in shallow seas off the coast of Laurentia after the previous supercontinent broke up and before the assembly of Pangaea. Limestone can erode fairly rapidly when exposed to the natural acidity of rainwater, enabling the growth of caves and valleys. Today only tiny Cedar Creek flows through this arch, but in the past it is thought that a larger creek, Cascade Creek, flowed through this site either through a crack in the limestone or through a cave that has since mostly collapsed. The flow of the larger creek eventually diverted once another nearby stream captured most of the water.

This site was a landmark in the Eastern United States throughout the first 100 years of its history. The 3rd United States President, Thomas Jefferson, purchased this land and built a guest retreat near the site. Many early presidents and other government figures spent nights near here. In 2016, this land was officially added as a Virginia State Park.

-JBB

Image credit: Virginia Parks https://flic.kr/p/MCGGAY

References: https://www.dmme.virginia.gov/commercedocs/RI_13.pdf http://www.naturalbridgeva.com/recreation/bridge-history/

Ófærufoss

This two-tiered waterfall tumbles over a pair of strong, basaltic lava layers in central Iceland. These falls occur where the Nydri-Ófæru river plunges over the edge of Eldgjá, a half-kilometer wide and 40 kilometer long crack in the ground. That canyon is a fissure, the remnant of a huge outpouring of volcanic lava over a thousand years ago.

The fissure system Laki, that erupted in 1783 is linked to a larger magma plumbing system, most likely of the volcano Grímsvötn. Similarly this fissure is likely linked to the volcanic plumbing system beneath Katla, a large and active volcanic complex near Iceland’s southern coast.

The lower tier of this waterfall formerly featured a natural bridge of igneous rock. However, that bridge collapsed during a flood in 1993.

-JBB

Image credits: https://flic.kr/p/HgxZ6e http://bit.ly/2425jNq

References: http://www.katlageopark.com/geosites/eldgja-ofaerufoss/ http://www.worldwaterfalldatabase.com/waterfall/Ófaerufoss-14650/ http://bit.ly/1TrfQNl

Sky view through Wild Horse Window, a large natural bridge in Utah near Goblin Valley.

Natural Bridge

Torndirrup National Park on Western Australia’s southern coast faces the ocean, along the coast where Australia and Antarctica split apart during the final breakup of Gondwanaland about 50 million years ago. Prior to that breakup, the two continental landmasses rode along the Earth’s surface together for over a billion years, following a continental collision.

Like most collisions of continental landmasses, Australia and Antarctica were brought together along a subduction zone. That subduction zone generated granites and granodiorites, including the rocks in this shot. These rocks formed about 1.2 or 1.3 billion years ago during that continental collision.

Rifting those continents apart exposed these granites to the ocean, where the erosive force of the waves now attacks them. Natural Bridge is one of several gaps scoured in the coastline by these waves. The park is now the most visited in Western Australia and was first listed as a park in 1918.

-JBB

Image credit: https://flic.kr/p/pxe9Gz

References: https://parks.dpaw.wa.gov.au/site/gap-natural-bridge http://www.topentity.com/porongurup-national-park/ http://bit.ly/1p695Zs

Running Eagle Falls, The Double Waterfall

Running Eagle Falls, or Pitamakan, is just one of over 200 waterfalls in Glacier National Park, Montana but it is unique in that it can be two waterfalls in one. For this reason it has also been called the Trick Falls. Erosion has created a natural bridge that spans the width of the falls. The lower falls flow year round and are about 6 m tall. During the spring, water flow from snowmelt is so high (average annual snowfall in Glacier is around 80 cm) that water will flow over the natural bridge, which is 12 m high. As seen below, there are many phases that the falls go through. During peak snowmelt times, the two falls are indistinguishable from each other as the upper falls completely overtake the lower falls (Left). As spring turns into summer, snowmelt flows subside and the upper falls become more a trickle (Top right). The last photograph was taken in late August 2014, when the upper falls have completely disappeared. This cycle has repeated itself for thousands of years, creating the truly unique waterfall seen below.

-JRA

Sources: http://www.nps.gov/features/glac/maps/runningea.htm http://www.hikinginglacier.com/running-eagle-falls.htm

Image Credits: National Park Service/Tim Rains http://bit.ly/1RObe4O National Park Service/Jacob W. Frank http://bit.ly/1RvpLQj Personal Collection of JRA