Javan Eruption

According to ENN, the Environmental News Network, hundreds of thousands of people on Indonesia´s main island of Java have been told to prepare for possible evacuation as officials Thursday predicted that a major volcano might erupt.
For the past few days, Mount Merapi has been spewing hot rock and ash as far as 1 1/2 miles from the crater rim, said Djumarma Wirakusumah, the director of Indonesia´s volcanological agency.

Volcanic Soil

Although volcanoes are often associated with destruction, there are positive effects. For example, volcanic eruptions produce a great deal of material which becomes very fertile soil.

Hot Spot or Not

A major puzzle in Earth science is how to explain the groups of volcanoes that don´t line up with subduction zones. These volcanic regions, called hotspots, occur in random-looking locations and don´t seem to move with any connection to the crustal plates. The prevailing theory about them is that magma bubbles straight up from deep in the mantle in hot columns called plumes. But a school of vigorous dissenters has been arguing for a top-down model of hotspots based on cooling from above, not heating from below.

Lahars

Some volcanoes have unstable slopes, and thus cause landslides when they erupt. Unfortunately the heat from the volcano can cause the landslides to be hot rivers of mud, especially if snow-covered slopes are melting from volcanic activity. In some eruptions, the near-boiling mudslides (lahars) have rolled through several unfortunate towns in their path.

Tsunamis

When earthquakes occur in the ocean, they can dislodge large volumes of water. This displacement travels across the ocean and, in shallow waters of bays and harbors, can result in tsunamis (sometimes erroneously called ´tidal waves´).

Tsunamis are extremely dangerous and unpredictable. People have been killed after earthquakes when they went to a nearby beach to watch for them. If you are in a coastal area and an earthquake occurs offshore, head for higher ground!!

What is a Plate, Exactly?

A plate is a segment of the lithosphere (the solid part of the earth, as opposed to the atmosphere or the hydrosphere). It includes the crust, which is the part we walk on, but also the upper part of the mantle, which is the layer of the planet that lies just below the crust.

Ring of Fire

Looking for the Ring of Fire? Check out the roughly circular zone of earthquake- and volcano-prone regions that run from western South America up through the west coast of North America, out through the Aleutians and down the east coast of Asia.

While volcanoes certainly occur other places, the Ring of Fire marks the most significant concentration of them, as well as some of the largest earthquakes.

Earthquake Prediction

A great deal of research has been devoted to the topic of earthquake prediction. It´s not easy, though, and the best we can do is use statistics to determine which areas are probably due for a quake soon. Earthquake hazard maps delineate areas with the greatest probability of experiencing significant shaking within the next 50 years.

Nuee Ardente

Many of us are familiar with Pompeii, the Italian village that was buried in ash when Vesuvius blew. The villagers were caught offguard and probably died when the volcano produced a nuee ardente, a hot cloud of poison gas. The cloud rolled down the mountainside and spilled into the village, killing the residents.

Measuring Earthquakes

Earthquakes can be measured several ways - by the magnitude of the earthquake wave as measured on a seismograph (that´s the Richter Scale, the one they talk about on TV) or by damage (the Mercalli Scale, which could vary from place to place).

The Richter Scale is logarithmic, which means that a quake of magnitude 5.0 causes a wave on a seismograph that is 10 times a magnitude 4.0 quake, and a 6.0 quake is 100 times the magnitude of a 4.0 quake. But it´s 30 times as much power. That means a 5.0 quake releases 30 times the energy of a 4.0 quake, and a 6.0 quake releases 900 times the energy of a 4.0 quake!

What causes earthquakes?

Earthquakes occur when rock layers move along a break, or fault, in the subsurface. Why is there movement? Turns out the Earth´s crust is broken up into large, country- or continent-sized plates which slowly move. Friction at plate boundaries builds up stress, like bending a ruler. If you bend a rule far enough, it will break - if the rocks drag against each other and build up enough stress, at some point they will break, too.

River Flow During Earthquakes

It´s believed that the flow of the Mississippi River was temporarily altered during the New Madrid earthquakes of 1811-1812. This happens when earthquake uplifts or depresses an abandoned channel. Even the direction of the flow of small streams can be permanently altered.

Scientists at the Univ. of Arkansas have studied this
phenomenon and a press release of their research
explaining the cause for this event can be found at http://www.pigtrail.uark.edu/news/2000/nov00/madrid.html

Measuring Earthquakes

Earthquakes are measured by several different scales. Two of the most popular are the Richter scale and the Mercalli Scale. The Richter Scale measures the amplitude of the wave printed out on a seismograph - the larger the wave, the greater the magnitude of the earthquake. It´s a logarithmic scale, by the way - that is, a 5.0 on the Richter Scale is 10 times as great a magnitude as a 4.0, and a 6.0 is 100 times the magnitude of a 4.0.

The Mercalli Scale, on the other hand, measures damage, and will vary from place to place - although usually the closer you are to the epicenter, the greater the damage (other things being equal).

Dangerous Volcanoes

Ever noticed that some volcanoes, like Mauna Loa in Hawaii, are reasonably well-behaved, while others, like Mt. St. Helens are dangerously explosive?

The difference lies in the type of lava involved. Oceanic volcanoes produce lava that flows more easily and doesn´t build up as much pressure inside the volcano. Continental volcanoes, on the other hand, produce a thicker, more viscous magma that flows poorly, and tends to build up pressure inside the volcano and could blow its top.

New Madrid Earthquake

In the winter of 1811-1812 three of the most powerful earthquakes in US history occurred - and they weren´t even in California! Although the Richter Scale (which measures earthquake magnitude) wasn´t around then, the Dec. 16th New Madrid quakes in central Mississippi was felt in Boston, Detroit, and New Orleans - it was the sparse population in the area that avoided many deaths.

Oceanic and Continental Crust

Oceanic crust is heavier, denser. It´s largely basalt, a heavy, black, fine-grained rock.

Continental crust is lighter than oceanic crust, and "floats" on it. It is largely granitic, mostly a lighter, coarse-grained material.