Category: Astronomy

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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

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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

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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

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Mount Vesuvius is a stratovolcano located on the western side of Italy, near Naples. It rises to an altitude of 1,281 meters above sea level; although the height of the volcano changes after each eruption. Vesuvius is best known for its devastating eruption in AD 79, which destroyed the towns of Pompeii and Herculaneum, burying the region under meters of ash, and killing an estimated 10,000 – 25,000 people.

It’s believed that the caldera of Mount Vesuvius started forming around 17,000 years ago and this was enlarged by further eruptions. It started forming because this is a point where the African Plate is being subducted beneath the Eurasian Plate. In the past, the larger cone on Vesuvius was Monte Somma, but it’s now lower than the main cone. The volcano Vesuvius continues to erupt regularly. The last eruption was in 1944, and then 1926, and in 1906. With this history, it’s just a matter of time before it has another eruption.

Although Italians remember the volcano’s history of eruptions, they continue to live on its slopes. There are productive vineyards part way down the mountain, growing in the rich volcanic soil. And an estimated 3 million people live in a region that could be affected if Vesuvius erupts again. Emergency planners in the region have developed a strategy to evacuate 600,000 people from the region if a severe eruption is expected.

We have written many articles about volcanoes for Universe Today. Here’s an article about stratovolcanoes, and here’s an article about Mount Etna; another dangerous volcano in Italy.

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.

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Did you know that volcanoes can make glass? Well, it’s not exactly the kind of glass you’d want to put in your house. It’s called obsidian, and it’s a naturally occurring volcanic glass formed when felsic lava flows from a volcano and then cools without crystal growth.

In a regular eruption, lava pours out of a volcano out onto the surface travels a distance downhill, and then hardens. Although a lava flow might have a thin solid crust, it might take months or even years to fully cool. As it cools, crystals form in the rock. These crystals are larger in the core of the rock, which has taken longer to cool.

In order to get obsidian, the lava erupting from a volcano needs to cool so fast that crystals in the rock don’t have a chance to form. You’ll often get obsidian when lava from a volcano is pouring into a lake or ocean and cools quickly. And glass, unlike crystals, has no regular structure and can therefore fracture in long curved shapes. Obsidian consists mostly of silicon dioxide (70% or more) – that’s the same as window glass. The black color comes from minerals dispersed in the glass, like magnetite or hematite.

If you could hold a piece of obsidian in your hand, it’s usually black or dark grey and very shiny and glasslike. It’s often cracked and broken with sharp edges. You can see than ancient people had many uses for obsidian, since it can hold a very sharp edge. In fact, surgeons to this day have found that obsidian can hold a sharper edge than even the hardest surgical steel.

We have written many articles about lava for Universe Today. Here’s an article about different types of lava, and here’s an article about the temperature of lava.

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.

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Lakes are formed by many different geologic processes, but one of the most dramatic is a maar. A maar is a low-relief crater caused by a phreatomagmatic eruption. This is a situation where ground water comes in contact with lava or magma and the resulting steam causes an explosion. This digs out a hole in the ground, creating the maar crater. And then, it usually fills back in to create a lake. The word “maar” comes from the German word, which is derived from the Latin word “mare” (sea).

Maars can occur anywhere in the world where magma comes in contact with ground water, and can range in size from 10 meters to 8 km across. They’re surrounded by a low rim composed of loose fragments of volcanic rocks and rocks torn from the ground when the explosive eruption happened. They can be 10 to 200 meters deep.

The largest known maar is found on the Seward Peninsula in northwest Alaska, and range in size from 4-8 km across. These maars are so large because the magma encountered large regions of permafrost, creating huge explosions.

A maar is related to a tuff ring. In the case of a tuff ring, the crater edge is raised above ground level. An even more dramatic tuff cone can rise up 300 meters above the surroundings.

Meteor crater in Arizona was once thought to be a maar, but geologists now know that it was created by a meteor impact about 50,000 years ago.

We have written many articles about volcanoes for Universe Today. Here’s an article about the parts of a volcano, and here’s an article about dormant volcanoes.

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.

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A volcano hotspot is a region on the Earth’s surface that has experienced volcanism for a long time. A good example of this is the Hawaiian Islands. Each of the islands in the long chain were created by the same volcano hot spot. The volcano built up an island that extended above the surface of the ocean, and then plate tectonics carried the island away, creating an extinct volcano. But there’s always a new volcano being created by the same hot spot.

There are dozens of volcano hot spots around the world, with the Hawaiian Island chain just being the most well known. Others include the Azores hotspot, the Canary hotspot and the East Australia.

About 30 km below the surface of the Earth is the mantle, a region where temperatures can reach thousands of degrees Celsius. But that’s under the continents. Underneath the oceans, the mantle is only 10 km down or less. Molten rock can seep out of the mantle and form vast magma chambers beneath the Earth’s crust. This magma finds its way to the surface, creating volcanoes.

Geologists believe that volcano hotspots are created when a narrow stream of hot mantle convects up from the Earth’s core-mantle boundary. This stream is known as a mantle plume.

Another theory is that hotspots are created when asteroids impact the Earth. The shockwave of the impact causes seismic waves to ripple through the Earth and create a hotspot on the exact opposite point on the Earth from the impact. This is known as the antipodal pair impact theory.

One of the most dramatic volcano hotspots wasn’t here on Earth but on Mars; the hotspot that created the largest volcano in the Solar System – Olympus Mons. Scientists believe that plate tectonics ceased on Mars billions of years ago, but the same volcanic hotspot kept pushing up magma. This allowed Olympus Mons to continue growing for billions of years, and reach its current height of 27 km.

We have written many articles about volcanoes for Universe Today. Here’s an article about dormant volcanoes, and here’s an article about extinct volcanoes.

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.