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Imaggeo

Imaggeo on Mondays: Isolated atoll

Imaggeo on Mondays: Isolated atoll

Covering a total area of 298 km², the idylic natural atolls and reefs of the Maldives stretch across the Indian Ocean. The tropical nation is famous for it’s crystal clear waters and picture perfect white sand beaches, but how did the 26 ring-shaped atolls and over 1000 coral islands form?

Coral reefs commonly form immediately around an island, creating a fringe which projects seawards from the shore. If the island is of volcaninc origin and slowly subsides below sea level, while the coral continues to grow growing outwards and upwards, an atoll is formed. They are usually roughly circular in shape and have a central lagoon. If the coral reef grows high enough, it will emerge from the sea waters and start to form a  tiny island.

“I took this photo while flying over the Maldives, south of Malè, from a small seaplane,” describes Favaro, who took this stunning aerial image of an atoll above the Indian Ocean.

Pictured, goes on to explain Favaro,

“[is] part of the ring-shaped coral reef bounding the atoll. On the right side of the image there is the lagoon and on the left side the open ocean. The coral reef is interrupted twice by ‘Kandu’ (water passages in Dhivehi [the language spoken in the Maldives]), which are the places where water flows in and out of the atoll when the tides changes”.

Two small harbours and antennas suggest the two small islands are occupied by local people, not by a resort or hotels.

“What always strikes me is how they can live so isolated, in a place which doesn’t offer basic resources, such as drinkable water,” says Favaro.

Fresh water is scarce in this archipelago nation. Rainwater harvesting is unreliable; poor rainfall means depleted collection tanks and groundwater tables. The problem is being exacerbated by climate change which is altering the monsoon cycle and rainfall patters over the Indian Ocean. As a result, the country relies heavily on desalination plants (and imported bottled water) to sustain the nation and the 1 million tourists who visit annually.

This animation shows the dynamic process of how a coral atoll forms. Corals (represented in tan and purple) begin to settle and grow around an oceanic island forming a fringing reef. It can take as long as 10,000 years for a fringing reef to form. Over the next 100,000 years, if conditions are favorable, the reef will continue to expand. As the reef expands, the interior island usually begins to subside and the fringing reef turns into a barrier reef. When the island completely subsides beneath the water leaving a ring of growing coral with an open lagoon in its center, it is called an atoll. The process of atoll formation may take as long as 30,000,000 years to occur. Caption and figure credit: National Oceanographic and Atmospheric Administration (NOAA).

References and further reading

How Do Coral Reefs Form? An educational resource by NOAA

Amazing atolls of the Maldives – a feature on NASA’s Earth Observatory.

 

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

Imaggeo on Mondays: What happens to mines when they become redundant?

Imaggeo on Mondays: What happens to mines when they become redundant?

When the minerals run out, or it is no longer profitable to extract the resources, mines shut down. Prior to issuing a permit for the exploitation of a resource, most regulators require assurance that once the mine closes it, or the activities carried out at the site, will not present a risk to human health or the environment.

Ongoing monitoring of a mine once it is decommissioned is required to ensure this is the case.

“The goal of my work is to study the environmental impact of mining waste in the north-east part of Algeria,” explains Issaad Mouloud, author of today’s featured image.

Algeria has a long history of mining. Since the antiquity and the time of the Berbers, many minerals and ores deposits were exploited. The northeast was the most productive region in the country. The geology of the study area is composed of magmatic and metamorphic rocks, sandstone and limestone.

Kef Oum Theboul mining district is located on the Eastern cost of Algeria, 4 km west of the Tunisian border. It is located 15 km from the town of El Kala. The Kef Oum Theboul site covers an area of 26.6 km2 and which contains copper lead and zinc ore

Discovered in 1845, the Kef Oum Teboul ore deposits were mined from 1849 to the 1970s. The Messida ore plant, pictured above and located not far from the Kef Oum Teboul deposit, is one of Issaad’s study sites.

The ore plant, situated in the Algerian Mediterranean coast, on Messida beach (located 6km from Kef Oum Teboul) processed copper, lead and zinc mineralizations.  Processing at the plant started in 1899.  It had three water jacket furnaces, with a capacity of 50 tons of ore per 24 hours. The obtained matte contained 20-22% copper, 200 grams of silver and 11-12 grams of gold per ton.

“The plant is now totally destroyed but mining waste, mainly sulphur ore and slag, is still stored in the Messida area,” explains Issaad, who goes on to say “the main pollution factor which I study is the acid mine drainage and heavy metals.”

 

Abandoned sulphurous ore and slag stored in the ruins of the ore processing plant of Messida. Credit: Issaad Mouloud

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: A prehistoric forest

Imaggeo on Mondays: A prehistoric forest

This stunning vista encompasses the south-western wilderness of Tasmania as seen from the Tahune air walk 60 m above the Huon river valley. In front lies the beginning of a huge UNESCO World Heritage Site, covering almost a fourth of the area of Tasmania. The site mostly consists of a pristine, temperate rainforest of Gondwanan origin that is home to the tallest flowering trees in the world; Eucalyptus spp. reach up to 100 m height in this region.

“I have never tasted the sense of a more remote place than this one. Give me more,” says Vytas Huth, who captured this stunning shot.

Gondwana was a supercontinent, consisting of present day Africa, South America, India, Madagascar, Australia and New Zealand. It formed when the even larger supercontinent of Pangaea broke up 250 million years ago.

Slowly, Gondwana started to break apart too. India tore away first, followed by Africa and then New Zealand. By the end of the Cretaceous, 65 million years ago, only South America, Australia and Antarctica remained joined.  It took a further 20 million years before Australia and Antarctica separated.

By the time Australia started being pulled northwards, the first glaciers were forming on Antarctica, as it began freezing over. Atop the old rocks which made up its bulk, animals and plants of ancient origin, travel northwards with the Land Down Under.

Because India and Africa broke away from the supercontinent so early on, few hallmarks of ancient Gondwana wildlife are left in their present biodiversity. In contrast, Australia and Tasmania remained connected to Antarctica and South America much longer and there are clear similarities in species across these continents.

“Fossil evidence suggests that temperate rainforest once extended across Australia, Antarctica, South America and New Zealand around 45 million years ago. Such fossils and the surviving species in Tasmania provide evidence of the ancient link to Gondwana”, reports the Tasmania Parks & Wildlife Service.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

Imaggeo on Mondays: Viñales Valley

Imaggeo on Mondays: Viñales Valley

From last week’s unusual desert landscape to this week’s lush valley in Cuba…

The picture shows the Vinales Valley, a karstic depression with mogotes in western Cuba. Karst is the general term for landscapes formed when limestone is disolved by carbonic acid, in rain water. This leads, in particular, to the formation of an underground network of caves and rivers.

In the tropics, due to the heavy rains, the dissolution is fast. The ground collapses above the caves and the karst landscape may evolve to mogotes, which are isolated and steep-sided limestone hills; visible in this week’s featured image. Mogotes can also be found in Eastern Asia, for instance in Halong Bay (Vietnam) or Bohol Island (‘Chocolate Hills’) in the Philipines.

By Alexis Merlaud, Belgian Institute for Space Aeronomy

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

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