Earth’s Magnetosphere interacting with solar wind
How the Mariana Trench Became Earth’s Deepest Point
Imaged Above: The Mariana Trench (pictured in a video still of an illustration) is the deepest place on Earth (Video still courtesy of NOAA)
The Mariana Trench isn’t really the deep, narrow furrow that the word “trench” implies. Rather, the abyss marks the location of a subduction zone.
Subduction zones occur where one part of the seabed—in this case the Pacific plate—dives beneath another, the Philippine plate. Though tectonic forces eventually warp the Pacific plate so that it makes a near-vertical dive into the Earth’s interior, at seabed level the plate dips at a relatively gentle angle.
A tectonic plate is a huge hunk of rock, 60 miles (97 kilometers) or more thick, said Robert Stern, a geophysicist at the University of Texas, Dallas. “In order for this to sink back into the earth, it has to bend downward, and these are very gentle bends.”
One reason the Mariana Trench is so deep, he added, is because the western Pacific is home to some of the oldest seafloor in the world—about 180 million years old.
Seafloor is formed as lava at mid-ocean ridges. When it’s fresh, lava is comparatively warm and buoyant, riding high on the underlying mantle.
But as lava ages and spreads away from its source, it slowly cools and becomes increasingly dense, causing it to settle ever lower—as is the case with the Mariana Trench.
Soil Classification
(Source: shoethongs)
2009 UNDERWATER ERUPTION IN THE SOUTH PACIFIC, SIX MILES OFF THE COAST OF TONGATAPU ISLAND, TONGA.
Arsia Mons, one of four volcanoes on Tharsis Rise, in a satellite picture.
Image courtesy THEMIS/NASA
Published December 3, 2010
As wide as the state of Arizona, Olympus Mons on Mars has long held the title of biggest volcano in the solar system. But if a new theory proves true, Olympus is about to be cast down.
In a recent paper, a team of geologists suggests that Olympus—along with the neighboring volcanoes Arsia, Pavonis, and Ascraeus—is just part of a much larger volcanic structure that stretches 4,350 miles (7,000 kilometers) across the red planet.
That would mean the gigantic raised plateau, known as Tharsis Rise, is the new volcanic record holder, the study authors say.
“If we look at it at this bigger scale, one can think of Olympus as a small parasitic cone that is part of Tharsis, just like all the other smaller volcanoes on Tharsis,” said study co-author Andrea Borgia, a visiting professor at The Open University in the U.K.
Mars Volcano Like a Big Mount Etna?
Using mathematical models, Borgia and co-author John Murray found that Tharsis Rise shares a lot of the same physical characteristics with one of Earth’s best studied and most active volcanoes, Mount Etna in Sicily.
(See “Italy’s Etna First Active Volcano to Get ‘CT Scan.’”)
Geologists classify Etna as a spreading volcano. This type of peak is built on a relatively weak rock layer, so that the erupting lava spreads out as the volcano builds mass and becomes heavier.
“It’s like if you build a pile of crystalline sugar on a table. The pile remains stable through time,” Borgia said. “However, if you build the same sugar pile on a layer of honey, the pile will spread laterally, collapsing at the center.”
Based on the models, Borgia thinks Tharsis Rise is simply a scaled-up version of Etna.
For example, Etna hosts smaller, so-called parasitic cones, which form when lava escapes from fractures other than the central volcanic vent. According to the study authors, Olympus Mons and the other three nearby volcanoes on Tharsis Rise could be similar features.
(Related: “Mars Volcanoes May Re-Erupt, Hawaii Comparison Shows.”)
“Small or large is not important. To have a volcano you need magma to be erupted through a crater and an edifice built by the accumulation of the erupted products,” Borgia said.
“Tharsis Rise is just a really big volcanic edifice.”
Hoping for a Field Trip
Proving the new theory may take some time, Borgia added, since getting the concrete truth may ultimately require either robotic or human explorers to be sent to this region of Mars.
Although the twin Mars rovers Spirit and Opportunity are in Mars’s equatorial region, neither rover is near Tharsis. And the four candidate landing sites for NASA’s Mars Science Laboratory, slated to launch late next year, aren’t close by either.
“Doing detailed field geology would be a very important step toward the demonstration of this thesis,” Borgia said.
“If they would allow me, I would go there right now!”
The Tharsis volcano research was published in February in a Geological Society of America Special Paper.
In June 2010, a team of scientists and intrepid explorers stepped onto the shore of the lava lake boiling in the depths of Nyiragongo Crater, in the heart of the Great Lakes region of Africa. The team had dreamed of this: walking on the shores of the world’s largest lava lake. Members of the team had been dazzled since childhood by the images of the 1960 documentary “The Devil’s Blast” by Haroun Tazieff, who was the first to reveal to the public the glowing red breakers crashing at the bottom of Nyiragongo crater. Photographer Olivier Grunewald was within a meter of the lake itself, giving us a unique glimpse of it’s molten matter.
The view from the volcano’s rim, 11,380 feet above the ground. At 1,300 feet deep, the lava lake has created one of the wonders of the African continent.
Even though the lava lake often overflows, the seven members of the expedition yearn to walk its shores. At the surface of the lake, bubbles of gas explode. The surface is permanently churned by fury from the earth’s crust.
Volcanic gases heat the base camp. Members often need to don gas masks for sleeping. At night, the base camp is illuminated by the light of the lava lake.
The goal of the expedition is to reach the rim of the lava lake. Nobody has previously survived such an encounter. Members of the team keep in contact through radio and relay data about the lava lake’s activities and the direction of the gases.
Franck Pothé approaches the lava. For such a close encounter, the wind must be at his back, pushing the heat away. Pothé is constantly informed of the swirling winds via radio contact with other members.
Marc Caillet is the first member of the team to reach the lake’s rim.
A major risk is the frequent overflows of the lake. Members surveying the lake from the second terrace help alert others to any threatening lava movements.
What an awesome planet we live on :,D
It’s kinda sad that the only reason I initially read this was ‘11,380’ jumped out at me.
My eye is trained to catch 1138 anywhere
Trinity was the code name of the first detonation of a nuclear device. This test was conducted by the United States Army on July 16, 1945. The date of the test is usually considered to be the beginning of the Atomic Age.
The above picture is the Trinity explosion, 0.016 seconds after detonation. The fireball is about 600 feet (200 m) wide. The black specks silhouetted along the horizon are trees.
