By Sara Thompson
Special to the Enterprise
Image credit is Lyn Topinka, from Wikimedia Commons.
The word ‘volcano’ comes from ‘Vulcan’ the fire god of Roman mythology. Around 75% of the world’s volcanoes are located in the Ring of Fire, an area ringing the Pacific Ocean and is also where many tectonic plate boundaries converge. There are a number of ways to classify volcanoes depending on size, shape, the ways it erupts, how the lava flows, chemical makeup of the resulting rocks, etc. The three most well-known varieties are called composite, cinder, and shield volcanoes.
Composite volcanoes are likely what most people think of when they think volcano. They are tall, steep, and often part of mountain ranges. They have a concave, conical shape, and will usually become steeper nearer the summit. They obtain their tall stature from countless eruptions and lava flows over time. The layering of the lavas continues to build up the mountainous volcano until it towers above all else. This type of volcano can be active over tens to hundreds of thousands of years. Even though they are formed by layered flows, they can have large, explosive eruptions. The famous eruption of Mount St. Helens in 1980 was from a composite volcano. The top may no longer exist, but now the volcano can continue to build itself back up again into the picturesque volcanoes in many of our minds.
Cinder volcanoes are the most common type of volcano in the world. They also have a cone-like shape but have a distinctive crater on the top. These volcanoes have an average height of 100-150 meters but can get as tall as 300 meters. They often have the igneous rock, scoria, surrounding them. Scoria are irregular-shaped stones with lots of cavities from gas bubbles inside. When cinder volcanos erupt, small blobs of lava are shot into the air and are cooled forming rock by the time they land. Cinder volcanoes have milder eruptions than other volcano types and have fewer “explosive” episodes.
Shield volcanoes are the largest volcano variety. They have gentle slopes and flatter summits, looking like shields laying on the ground, which gives them their name. They are built by intermittent eruptions over millions of years. The largest active volcano on the planet is a shield volcano. Mauna Loa is over 10,000 meters tall from its base on the sea floor. All the volcanoes that created the Hawaiian Islands are shield volcanoes, and even though they are close together, they have separate magma chambers making them all separate volcanos.
Volcanic eruptions can be devastating to witness, but areas with volcanic activity have some of the most fertile soil from the minerals present in volcanic ash and rocks. It can be strange to think of the same thing that brings destruction can also help life thrive. Learn more about volcanoes and igneous rocks at our exhibit “Explorit Rocks!”. Open to the public on Fridays from 1-4pm, Saturdays and Sundays from 10am-2pm. Admission is $5 per person. Explorit Members, ASTC, and those age 2 and under free.
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