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Archive for the ‘ASTER’ Category

Images of the Day: Tonga Islands Grow Larger

Posted by feww on March 28, 2009

New Landmass Formed by Hunga Tonga-Hunga Ha’apai Eruption

Submarine Eruption in the Tonga Islands


Image acquired March 26, 2009


Image acquired November 14, 2006

In mid-March 2009, a plume of ash and gas burst out of the ocean as an undersea volcano began to erupt in the South Pacific nation of Tonga. Small sections of the rim of the large undersea volcano had been above water, forming the islands of Hunga Tonga and Hunga Ha’apai. The eruption occurred at two vents, one submerged and the other on Hunga Ha’apai. The eruption pumped out enough rock and ash that by March 25, when the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite captured the top image, the submerged vent was surrounded by new land.

The new land is the dark mass south of Hunga Ha’apai. It had not been present when ASTER acquired the lower image on November 14, 2006. In the March 25 image, clouds cover the space between the new land and Hunga Ha’apai, but news reports indicate that the new land connects Hunga Ha’apai with the underwater vent, essentially enlarging the small island. The vent itself is the nearly perfect circular hole near the southern edge of the new land.

The image reveals some of the other impacts of the eruption. The ocean around the erupting volcano is bright blue, likely colored with ash, rock, and other volcanic debris. The eruption also killed or damaged plants on Hunga Ha’apai. In these false-color images, plant-covered land is red. In 2006, Hunga Ha’apai had supported vegetation, but after the eruption, the island was black. Either the plants were buried in ash or dead in the wake of the eruption. According to a visiting reporter, the eruption destroyed plant and birdlife on the island, leaving blackened tree stumps and dead birds and fish.

NASA image created by Jesse Allen, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. Caption by Holli Riebeek.Instrument: Terra – ASTER

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Lonar Crater

Posted by feww on April 16, 2008

Lonar Crater, India

India’s Lonar Crater began causing confusion soon after it was identified in 1823 by a British officer named C.J.E. Alexander. Lonar Crater sits inside the Deccan Plateau—a massive plain of volcanic basalt rock leftover from eruptions some 65 million years ago. Its location in this basalt field suggested to some geologists that it was a volcanic crater. Today, however, Lonar Crater is understood to result from a meteorite impact that occurred between 35,000 and 50,000 years ago.

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) flying on NASA’s Terra satellite acquired this image of Lonar Crater on November 29, 2004. In this simulated-true-color image, pink-beige indicates bare ground, blue and off-white indicate human-made structures, dark blue indicates water, green indicates vegetation, and dull purple indicates fallow fields. A vegetation-lined lake fills the crater, one of the few natural features of this scene. Signs of human habitation surround the lake, especially the cluster of blue and off-white points to its immediate northeast. Outside of this settlement, the vicinity is a patchwork of agricultural fields.

Lonar Crater is approximately 150 meters (500 feet) deep, with an average diameter of almost 1,830 meters (6,000 feet). The crater rim rises roughly 20 meters (65 feet) above the surrounding land surface. Scientists established Lonar’s status as an impact crater based on several lines of evidence, perhaps the most compelling being the presence of maskelynite. Maskelynite is a kind of naturally occurring glass that is only formed by extremely high-velocity impacts. A Science article published in 1973 pointed out this material’s presence, and suggested that the crater’s situation in volcanic basalt made it a good analogue for impact craters on the surface of the Moon.

References

  • Fredriksson, K., Dube, A., Milton, D.J., Balasundaram, M.D. (1973). Lonar Lake, India: An impact Crater in basalt. Science. 180, 862-864.
  • Khagol Mandal. Lonar Meteoritic Crater. Accessed April 11, 2008.
  • Wikipedia. Deccan Plateau. Accessed April 11, 2008.

NASA image created by Jesse Allen, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. Caption by Michon Scott.

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