Universe Today

Mount Pinatubo is an active stratovolcano on the island of Luzon in the Philippines, and the site of one of the most powerful recent eruptions. In June 1991, the volcano produced the second largest terrestrial eruption of the 20th century (after Novarupta), and the largest eruption in living memory. At least 800 people lost their lives in the eruption, but this was lower than it could have been because of an organized evacuation effort.

Pinatubo is located in the Cabusilan Mountain range, located on the west coast of the Island of Luzon. It’s a stratovolcano made up of successive layers of andesite and dacite. Its richly forested slopes were home to several thousand indigenous people. Before the eruption, it rose to an elevation of 1745 meters, but now it’s only 1485 meters tall.

Scientists had many warnings that Pinatubo was about to erupt, and this allowed such a thorough evacuation. On July 16, 1990, a magnitude 7.8 earthquake struck about 100 km north of Pinatubo. And then in March/April 1991, molten rock was detected rising to the surface from more than 32 kilometers beneath Pinatubo. This triggered more small earthquakes through April, May and early June.

On June 12, 1991, millions of cubic meters of magma reached the surface, beginning several days of eruptions. Even more magma reached the surface on June 15th, ejecting more than 5 cubic kilometers of material. An ash cloud rose 35 kilometers into the air, covering the surrounding region in meters of ash. Dangerous pyroclastic flows of hot ash, rock and water surged down the sides of the volcano, destroying everything in their path. The huge eruption gouged out a caldera 2.5 km across.

The eruption was so significant that the ash darkened the atmosphere, and caused worldwide temperatures to drop by 0.5 degrees C.

We have written many articles about volcanoes for Universe Today. Here’s an article about Mount St. Helens, and here’s an article about Krakatoa.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

[/caption]
The most powerful and devastating volcanic eruption in the history of the United States was the explosion of Mount St. Helens. This active stratovolcano, located in Skamania County, Washington detonated on May 18, 1980, killing 57 people, destroying hundreds of homes, and flattening hundreds of square kilometers of forest. The eruption tore off the top of the mountain, reducing its height from 2,950 meters to 2,550 meters.

Mount St. Helens is just one volcano in the Cascade Range of mountains that stretch down the west coast of North America. There are many other famous volcanoes in this region, like Mount Ranier, Mount Hood, and Mount Shasta. Helens is a large eruptive cone made up of several layers of lava rock interlaced with ash, pumice and other deposits. There are layers of basalt and andesite, and several domes of dacite lava have broken through.

Scientists believe that Mount St. Helens started forming about 40,000 years ago, and it’s considered the most active volcano in the Cascade Range. Before its eruption, St. Helens was the 5th-highest peak in Washington state; it was nicknamed the Mount Fuji of America. It measures about 10 km across the base and rose about 1,500 meters above the surrounding landscape.

And so, on May 18, 1980, Mount St. Helens erupted catastrophically, after nearly 2 months of local earthquakes and steam eruptions – scientists measured more than 10,000 minor earthquakes leading up to the eruption. But it was a magnitude 5.1 earthquake on May 18th that caused the volcano’s bulging north flank to slide away in the largest landslide in recorded history. This released a huge blast of hot gas, steam and rock debris that swept downhill from the summit. This pyroclastic flow melted snow and ice on the mountain, which added to the torrent of material streaming down the river valleys leading from the volcano. A plume of ash rose 19 kilometers into the air, covering 57,000 square kilometers of the Western United States.

Mount St. Helens is still active, and scientists have discovered dozens of extrusions of thick, pasty lava. A new dome is taking shape. It’s now about 1,100 meters in diameter and 250 meters tall.

We have written many articles about volcanoes for Universe Today. Here’s an article about Kilauea in Hawaii, and here’s an article about Krakatoa.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

References:
http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/summary_may18_eruption.html
http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/Bulletin1859/eruption_may18_1980.html

[/caption]
The Hawaiian Island chain is a long string of islands that actually stretches for thousands of km. All of these islands were formed by the movement of the Pacific plate above a volcanic hotspot. As the plate is constantly slowly moving, it allowed volcanic islands to form and then carried them away so they would become extinct. There are 5 shield volcanoes on the Big Island of Hawaii, with Kilauea being the newest and most active.

Kilauea is located on the Eastern edge of the Big Island of Hawaii. It rises only 1,247 km above sea level; a fraction of its neighbor Mauna Loa, which rises to 4,169 km. It’s classified as part of a family of low, broad volcanoes known as shield volcanoes. The basaltic lava that erupts out of shield volcanoes has a low viscosity which can flow for dozens of kilometers. While the other volcanoes on the island are extinct or dormant, Kilauea is in an almost constant state of eruption.

Scientists used to think that Kilauea was a satellite volcano of the larger Mauna Loa, but better research has shown that Kilauea has its own magma plumbing system, starting more than 60 km below the surface of the Earth. Kilauea has almost continuous activity during the 19th century, and there were 34 eruptions since 1952. In January 1983, eruptions began along the east rift zone and haven’t stopped since.

Kilauea is one of the most accessible volcanoes in the world. You can drive right up to it, park, and walk down a short trail to peer into the volcano crater. There’s even a lodge on the ridge that gives an amazing view of the volcano. One of the best ways to view Kilauea is by boat. Tours will take visitors just offshore, where hot lava is pouring out of Kilauea and into the Pacific Ocean. This creates huge plumes of steam.

The inhabitants of the Hawaiian Islands believed that the goddess of volcanoes, Pele, lived in Kilauea. They thought that eruptions happened when their goddess was angry, and they developed many tribal chants to try and calm her down. Several unique lava formations are named after her, like Pele’s tears (small drops of lava that cooled in mid air during an eruption), and Pele’s hair (strands of volcanic glass).

We have written many articles about volcanoes for Universe Today. Here’s an article about Mount Vesuvius, and here’s an article about Mount Etna.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Reference:
USGS Volcano Information Page: Kilauea

[/caption]
Perhaps the most famous volcanic eruption in recent history is the explosion of the volcano Krakatoa in 1883. On August 27 a series of four explosions almost entirely destroyed the island. People as far away as Perth in Western Australia could hear the detonation, and it’s estimated that 120,000 people died from the eruption. In fact, the entire climate of Earth was affected for several years after the eruption, as global temperatures dipped for 5 years.

What’s left of Krakatoa is a small group of islands located in the Sunda Strait, which divides Sumatra from the Island of Java. It’s located directly above the subduction zone of the Eurasian Plate and the Indo-Australian Plate, where the plates make a change in direction. It’s believed that the volcano’s caldera collapsed in 416 AD, forming a 7-km wide caldera. The remnants of this eruption formed Verlaten and Lang Islands. Three volcanoes (Rakata, Danan and Perbuwatan) came together to form the pre-1883 Krakatau island.

Krakatau was made up of one or more stratovolcanoes that went through 5 major periods. The first was an early growth phase, followed by the formation of the caldera. Then the caldera collapsed, and was destroyed during the 1883 eruption. A new growth phase began in December 27, and even now Krakatoa is growing by more than 12 cm/year.

The destruction of Krakatoa began on May 20, 1883 when a mild ash and steam eruptions started up. There were similar eruptions for about 3 months, and at times several vents were erupting at the same time. On August 11, large ash columns rose from the main crater of Perbuwatan. These small eruptions intensified over time, leading to the August 27th explosion that caused the collapse of the caldera.

Although the eruption of Krakatau was devastating, scientists think that many people lost their lives from the giant tsunami generated by the eruption. The largest wave reached 40 meters and killed around 34,000 people. In one case, a ship was carried 2.5 kilometers inland and dumped into the forest.

Scientists measuring the strength of volcanic eruptions using a scale called the Volcanic Explosivity Index (VEI). The eruption at Krakatau measured VEI 6 on the scale, and ejected 16 cubic kilometers of material. Anything within 16 km was covered with 16 meters of ash. Even towns located more than 450 km away were coated with a few cm of ash.

We have written many articles about volcanoes for Universe Today. Here’s an article on Mount Etna, and here’s an article on Mount Vesuvius.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

References:
http://vulcan.wr.usgs.gov/Volcanoes/Indonesia/description_krakatau_1883_eruption.html
http://hvo.wr.usgs.gov/volcanowatch/2003/03_05_22.html

[/caption]

An international team of astronomers has mapped the density and temperature of X-ray-emitting gas in the outskirts of a distant galaxy cluster.   The results, obtained with the orbiting Japanese X-ray telescope Suzaku, give the first complete X-ray view of a galaxy cluster, and provide insight into how such clusters come together.

“These Suzaku observations are exciting because we can finally see how these structures, the largest bound objects in the universe, grow even more massive,” said Matt George, the study’s lead author at the University of California, Berkeley.

The team trained Suzaku’s X-ray telescopes on the massive galaxy cluster PKS 0745-191, which lies 1.3 billion light-years away in the southern constellation Puppis.  Between May 11 and 14, 2007, Suzaku acquired five images of the million-degree gas that permeates the cluster.

The X-ray images of the cluster helped astronomers measure the temperature and density of the gas.  These provide clues about the gas pressure and cluster’s total mass.  The hottest, densest gas lies near the cluster’s center, while gas temperature and density steadily decline away from the center.

Astronomers believe the gas in the inner part of a galaxy cluster has settled into an ordered “relaxed” state in equilibrium with the cluster’s gravity.  But in the outer regions, where galaxies first begin a billion-year plunge towards the cluster’s center, the gas remains in a disordered state because it’s still falling inward.

“Clusters are the most massive, relaxed objects in the universe, and they are continuing to form now,” said team member Andy Fabian at the Cambridge Institute of Astronomy in the UK.

For the first time, this study shows X-ray emission and gas density and temperature out to the region where the gas is disordered, and where the cluster continues to assemble.

“It gives us the first complete X-ray view of a cluster of galaxies”, said Fabian.

In PKS 0745-191, the gas temperature peaks at 164 million degrees Fahrenheit (91 million C) about 1.1 million light-years from the cluster’s center. The temperature declines smoothly with distance, dropping to 45 million F (25 million C) more than 5.6 million light-years from the center.

To accurately measure X-ray emission at the cluster’s edge requires detectors with exceptionally low background noise.  Suzaku has advanced X-ray detectors, and it lies in a low-altitude orbit near the Earth’s magnetic field, which protects the observatory from energetic particles from the sun and beyond.

“With more Suzaku observations in the outskirts of other galaxy clusters, we’ll get a better picture of how these massive structures evolve,” added George.

Suzaku (Japanese for “red bird of the south”) was launched on July 10, 2005. The observatory was developed at the Japanese Institute of Space and Astronautical Science (ISAS), which is part of the Japan Aerospace Exploration Agency (JAXA), in collaboration with NASA and other Japanese and U.S. institutions.

The results were published in the May 11 edition of the Monthly Notices of the Royal Astronomical Society.

Source: NASA