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Mary Greeley

Lost microcontinent lurking under the sea

By Charles Q. Choi, OurAmazingPlanet Contributor | LiveScience.com

Photo By Torsvik, et al./Nature GeoScience

The remains of a micro-continent scientist call Mauritia might be preserved under huge amounts of ancient lava beneath the Indian Ocean, a new analysis of island sands in the area suggests.

These findings hint that such micro-continents may have occurred more frequently than previously thought, the scientists who conducted the study, detailed online Feb. 24 in the journal Nature Geoscience, say.

Researchers analyzed sands from the isle of Mauritius in the western Indian Ocean. Mauritius is part of a volcanic chain that, strangely, exists far from the edges of its tectonic plate. In contrast, most volcanoes are found at the borders of the tectonic plates that make up the surface of the Earth.

Investigators suggest that volcanic chains in the middle of tectonic plates, such as the Hawaiian Islands, are caused by giant pillars of hot molten rock known as mantle plumes. Theserise up from near the Earth's core, penetrating overlying material like a blowtorch. [What Is Earth Made Of?]

Mantle plumes can apparently trigger continental breakups, softening the tectonic plates from below until they fragment — this is how the lost continent of Eastern Gondwana ended about 170 million years ago, prior research suggests. A plume currently sits near Mauritius and other islands, and the researchers wanted to see if they could find ancient fragments of continents from just such a breakup there.

Digging in the sand

The beach sands of Mauritius are the eroded remnants of volcanic rocks created by eruptions 9 million years ago. Collecting them"was actually quite pleasant," said researcher Ebbe Hartz, a geologistat the University of Oslo in Norway. He described walking out from a tropical beach, "maybe with a Coke and an icebox, and you dig down underwater into sand dunes at low tide."

Within these sands, investigators discovered about 20 ancient zircon grains (a type of mineral) between 660 million and 1,970 million years old. To learn more about the source of this ancient zircon, the scientists investigated satellite maps of Earth's gravity field. The strength of the field depends on Earth's mass, and since the planet's mass is not spread evenly, its gravity field is stronger in some places on the planet's surface and weaker in others.

The researchers discovered Mauritius is part of a contiguous block of abnormally thick crust that extends in an arc northward to the Seychelles islands. The finding suggests Mauritius and the adjacent region overlie an ancient micro-continent they call Mauritia. The ancient zircons they unearthed are shards of lost Mauritia.

The researchers meticulously sought to rule out any chance these ancient grains were contaminants from elsewhere.

"Zircons are heavy minerals, and the uranium and lead elements used to date the ages of these zircons are extraordinarily heavy, so these grains do not easily fly around — they did not blow into Mauritius from a sandstorm in Africa," Hartz told OurAmazingPlanet.

"We also chose a beach where there was no construction whatsoever — that these grains did not come from cement somewhere else," Hartz added. "We were also careful that all the equipment we used to collect the minerals was new, that this was the first time it was used, that there was no previous rock sticking to it from elsewhere."

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Sulphur mining in an active volcano

By Megan Lane BBC News

 

Extracting sulphur - once known as brimstone - from Ijen volcano

Matches and white sugar are among the products made with sulphur hewn by hand from an active volcano in Indonesia. Is this one of the most dangerous jobs in the world?

Kawah Ijen volcano

• 2,600m (8,660ft) tall, last erupted 1999 with ash but not magma
• In Pacific 'Ring of Fire' of 130 active volcanoes
• Yellow area, left of picture, is solidified sulphur
• Crater lake 1km across, and its water has pH of 0.5 - similar to battery acid

The traditional sulphur miners of East Java bear the scars of their labour - poisoned lungs and skin criss-crossed with burns and scars.

Several hundred men work in the heart of Ijen volcano in East Java, Indonesia. Each day, they collect yellow lumps of sulphur that solidify beside its acidic crater lake. Once processed, the sulphur is used to bleach sugar, make matches and fertiliser, and vulcanise rubber in factories at home and abroad.
Filmed for the BBC's Human Planet, the miners carry 90kg loads up 200 metres out of the crater and back down the volcano's outer slopes to a weighing station - a journey they make several times a day.
"There are many big mountains but only one gives us the sulphur we need," says Sulaiman, 31, who has mined the crater for 13 years.
The miners have little in the way of protective gear beyond a damp cloth to cover the nose and mouth. Gloves and gas masks are an unaffordable luxury for men paid $10 to $15 a day.
In the past 40 years, 74 miners have died after being overpowered by fumes that can suddenly swirl from fissures in the rock. The poisonous clouds are not steam, but hydrogen sulphide and sulphur dioxide gases so concentrated they burn the eyes and throat, and can eventually dissolve the miners' teeth.

Gas meter ready: Watch Ijen's toxic gas roll in

During filming, the BBC crew was enveloped in a toxic cloud 40 times the UK's safe breathing level (no limits exist for the miners). Corrosive air-borne particles ate into the cameras, which promptly broke down.
It is a method of sulphur extraction that has all but died out, says volcanologist Clive Oppenheimer, of Cambridge University. "Until the late 19th Century, there were sulphur mines in volcanic countries such as Italy, New Zealand, Chile and Indonesia."
Eruptions, and the advent of new processes, led to the closure of most mining operations.
"There are still volcanic sulphur mines in the Andes, but these are mechanised," says Dr Oppenheimer.

An active vent close to the lake shore is used for the sulphur mining operation. The water in the crater - which is one of the world's largest - is acidic enough to dissolve clothes, eat through metal, and cause breathing problems.

Pipes are driven into the fissures in the rock to extract sulphur from the bowels of the mountain. It is blood red when molten, and turns yellow as it cools and solidifies.

The miners break the cooled sulphur into chunks, and load up their wicker baskets for the 200 metre climb back up out of the crater.

Each man carries up to twice his body weight from the crater to the weighing station part way down the mountain.

The work takes a toll on their bodies. But their bodies have, in turn, adapted. Many can hold their breath for extended periods, like the freediving Bajau fishermen of Malaysia, and some have hyper-developed shoulder muscles from years of lugging heavy baskets up and down the mountain, says BBC researcher Dina Mufti.
"Our families worry when we come here. They say working here can shorten your life," says Hartomo, 34, a sulphur miner for 12 years.
"I do it to feed my wife and kid. No other job pays this well," adds Sulaiman.

Indonesia's Infamous Mud Volcano Could Outlive All of Us

Since it roared to life in May 2006, a mud volcano near Indonesia's coastal city of Sidoarjo has swallowed homes, rice paddies, factories, and roads, killing 15 people, displacing 40,000, and harming the livelihoods of many more. As the ongoing eruption nears its 5th anniversary, observers wonder whether it will ever stop. The answer: Not anytime soon. A new study predicts the volcano will continue spewing significant amounts of mud for another 2 decades. A second study forecasts that it could grind on as long as 87 years.

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Indonesia's Infamous Mud Volcano Could Outlive All of Us