Answers to Exploration Questions: Volcanoes

1. Identify the type of volcano shown here. Then explain the relationship between the composition of its magma, the way it erupts, and its shape.

ANSWER: This is a shield volcano. The magma in these volcanoes is low in silica and low in gas, so it does not erupt explosively. Instead, it oozes thin, runny lava that spreads over a wide area. The layers and layers of lava build up to form the volcano’s wide, gentle slopes.

ANSWER: Hot spots cause mantle to melt. The magma rises up and breaks through the overlying plate. The hotspot stays in one place, but the tectonic plate above it moves. As the plate moves, so does the volcano.  The volcano that moved away from the hot spot becomes extinct, and another one forms right above the hot spot. This process continues, forming a line of extinct volcanoes.

ANSWER: This image was produced with an infrared camera. These cameras produce thermal imaging of volcanoes, which reveals the temperature distribution of the volcano — where it’s warmer and where it’s cooler. Thermal imaging can reveal where magma is rising beneath a volcano—a sign that it could erupt. It can also reveal the presence of hidden fractures where magma may be moving towards the surface.

4. Explain what’s happening in this picture. How does this lead to volcanic eruptions?

ANSWER: This picture shows a volcano forming at a subduction zone. When an oceanic plate collides with a continental plate, it sinks into the mantle below. As the oceanic plate sinks, fluid (shown in purple) is squeezed out of it. The fluid flows up into the mantle rock above and changes its chemistry, causing it to melt. This forms magma (molten rock – shown in orange). The magma rises and collects in chambers within the crust. As magma fills the chamber, pressure grows. If the pressure gets high enough, the magma can break through the crust and spew out in a volcanic eruption.

ANSWER: Yellowstone has geysers, mud pots, pools of hot water that smell like hydrogen sulfide—all evidence that a magma chamber below heats the area. There are also remnants of calderas that formed after parts of the magma chamber collapsed. Finally, scientists are tracking changes such as ground level rises and seismic activity.

Photo credits: volcano, Nula666 via Wiki Commons; tools and illustrations, © AMNH.