Reading Practice Test Demo

One of the earth’s most spectacular activities is a volcanic eruption. Volcanos erupt when magma, hot liquid rock originating below the surface of the earth, is forced up through a fissure to the earth’s surface. Volcanos have been known to destroy entire islands and send out shock waves in the form of seismic sea waves or tsunami for thousands of miles. The devastation is often widespread as molten lava, rocks, and gas are thrown out, forming cones. After the volcano has erupted, a crater forms where the magma once flowed to the surface. A crater is a hollow depression in the earth’s surface and may be the site of another volcano months or years later. If the crater and top section of the volcano are missing, a caldera, much wider than the crater, forms. Calderas fill in the section where the cone once was. Some small islands in the middle of former islands destroyed by volcanic activity are really calderas. Anyone can see that the earth’s surface is greatly changed by volcanic eruptions.

One such eruption occurred on August 27, 1883, when Krakatoa, an Indonesian island, experienced the greatest volcanic explosion people have ever recorded. More than 36,000 people died when their villages were destroyed. The volcanic rock was so fragmented when it exploded that it reached the stratosphere and was carried by wind currents all around the world. The dust of these fragments caused beautiful red sunsets for several years. Another result was the tsunami which sped across the ocean, sinking many ships and damaging other islands. The force of this volcano was heard throughout an eighth of the world!