Volcano Land Formations

In 1816, Chauncey Jerome, a resident of Connecticut, wrote that the clothes his wife had laid out to dry the day before had frozen during the night. This event would not have been unusual except that the date was June 10!

At the time, residents of New England did not know that the explosion of a volcanic island on the other side of the world had severely changed the global climate and was causing “The Year Without a Summer.”

The explosion of Mount Tambora in 1815 blanketed most of Indonesia in darkness for three days. It is estimated that 12,000 people died directly from the explosion and 80,000 people died from the resulting hunger and disease. The global effects of the eruption were not felt until the next year, however. During large-scale eruptions, enormous amounts of volcanic ash and gases are ejected into the upper atmosphere.

As volcanic ash and gases spread throughout the atmosphere, they can block enough sunlight to cause global temperatures to drop. The Tambora eruption affected the global climate enough to cause food shortages in North America and Europe. More recently, the eruption of Mount Pinatubo, from the video “Killer Volcano,” caused average global temperature to drop by as much as 0.5*C. Although this may seem insignificant, such a shift can disrupt climates all over the world.

Volcanic eruptions create many landforms from lava and gas and from magma.

Landforms from Lava and Ash Shield Volcano – lava flows out gradually in a nonexplosive eruption, building a wide, gently sloping mountain. Although the sides are not steep, the volcano can be enormous.

Cinder Cone Volcano – when lava has high viscosity it produces ash, cinders and bombs which all build up around the vent in a steep, cone-shaped hill or small mountain. They are small and usually erupt for only a short time. They usually form on the sides of other volcanoes.

Composite Volcano – tall, cone-shaped mountains formed from explosive eruptions followed by quieter flows in which layers of lava alternate with layers of ash; sometimes called stratovolcanoes.

Lava Plateaus – high, level area that has been built up over time (millions of years) from lava seeping out of several cracks, or rifts, then traveling a distance before cooling and solidifying.

Crater – a funnel-shaped pit near the top of the central vent of a volcano

Caldera – huge hole, many times larger than a crater, left when the magma chamber below a volcano partially empties and causes the ground above to sink

Landforms from Magma Volcanic necks – forms when magma hardens in a volcano’s pipe; softer rock around the pipe wears away exposing hard rock

Dikes – formed when magma forces itself across rock layers and hardens Sill – formed when magma squeezes between horizontal layers of rock

Batholiths – mass of rock formed when a large body of magma cools inside the crust Dome mountain – forms when an uplift pushes a batholith or smaller body of hardened magma toward the surface