Chapter 3 Volcanoes

How is volcanic activity on the moons of Jupiter and Neptune different from volcanic activity on Earth?

Io and Triton have volcanic features very different from those on Earth, Mars, and Venus. On Io, sulfur volcanoes erupt like fountains or spread out like umbrellas above the colorful surface. The eruptions on Triton involve nitrogen. It is possible that heat from the sun melts some of the frozen nitrogen underneath Triton's surface. The liquid nitrogen then expands and erupts through the planet's icy crust.

What process forms island arcs?

Island arcs are formed from subduction. Magma forming from the subducting plate seeps upward through cracks in the crust and breaks through the ocean floor, creating volcanoes.

What causes hot spot volcanoes to form?

Magma from deep within the mantle melts through the crust above it.

Where do most volcanoes occur on Earth's surface?

Most volcanoes occur along diverging plate boundaries, such as the mid-ocean ridge, or in subduction zones around the edges of oceans.

Describe how a dome mountain can eventually form out of magma that hardened beneath Earth's surface.

A dome mountain forms when rising magma is blocked by horizontal layers of rock. The magma forces the layers of rock to bend upward into a dome shape. Eventually, the rock above the dome mountain wears away.

Compare and contrast quiet and explosive volcanoes.

A volcano erupts quietly if its magma flows easily. Quiet eruptions produce two different types of lava: pahoehoe and aa. Lava flows pour from vents, setting fire to and then burying everything in their path. If its magma is thick and sticky, a volcano erupts explosively. During an explosive eruption, a volcano can belch out hot, burning clouds of volcanic gases as well as cinders and bombs. Although quiet eruptions and explosive eruptions involve different volcano hazards, both types of eruption can cause damage far from the crater's rim.

What are the stages that lead up to a volcanic eruption?

Because liquid magma is less dense than the surrounding solid material, magma flows upward into any cracks in the rock above. As magma rises toward the surface, the pressure decreases. The dissolved gases begin to separate out, forming bubbles. A volcano erupts when an opening develops in weak rock on the surface. During a volcanic eruption, the gases dissolved in magma rushes out, carrying the magma with them.

Explain the formation of a volcanic landform that can result when a volcano uses up the magma in its magma chamber.

Enormous eruptions may empty the main vent and the magma chamber beneath a volcano. The mountain becomes a hollow shell. With nothing to support it, the top of the mountain collapses inward. The huge hole left by the collapse of a volcanic mountain is called a caldera.

What will eventually happen to the active volcano on the island of Hawaii, which is now over the hot spot?

Eventually, the plate's movement will carry the island of Hawaii away from the hot spot.

What features form as a result of magma hardening beneath Earth's surface?

Features formed by magma include volcanic necks, dikes, and sills, as well as batholiths and dome mountains.

Describe the process that creates a lava plateau.

First, lava flows out of several long cracks in an area. The thin, runny lava travels far before cooling and hardening. Again and again, floods of lava flows on top of earlier floods. After millions of years, these layers of lava can form high plateaus.

Describe five landforms formed from lava and ash.

Rock and other materials formed from lava and ash create a variety of landforms including shield volcanoes, composite volcanoes, cinder cone volcanoes, calderas, and lava plateaus. Repeated lava flows during quiet eruptions gradually build up a broad, gently sloping volcanic mountain known as a shield volcano. Layers of lava alternate with layers of ash, cinders, and bombs in a composite volcano, which has both quiet and explosive eruptions. When cinders erupt explosively from a volcanic vent, they pile up around the vent, forming a cone-shaped hill called a cinder cone. A caldera is the large hole at the top of a volcano formed when the roof of a volcano's magma chamber collapses. The hole is filled with pieces of the volcano that have fallen inward, as well as lava and ash. Some eruptions of lava form high, level areas called lava plateaus.

What is the largest volcano in the solar system? What type of volcano is it?

The biggest volcano on Mars is the largest mountain in the solar system. This volcano, Olympus Mons, is a shield volcano similar to Mauna Loa on the island of Hawaii, but much, much bigger.

How do the volcanoes on Venus compare with the volcanoes on Mars?

There are far fewer volcanoes on Mars than on Venus. Olympus Mons on Mars is over eight times taller than Theia Mons on Venus. The volcanoes on Mars and Venus don't seem to be active, but have a long history of volcanic activity.

A geologist times a passing lava flow at 15 kilometers per hour. The geologist also sees that lava near the edge of the flow if forming smooth-looking ripples as it hardens. What type of lava is this? What type of magma produced it? Explain your conclusions.

This type of lava is pahoehoe. It is fast-moving, hot lava that hardens into a rippled surface. The type of magma that produce it must be basalt. Basalt, a dark-colored volcanic rock, forms from low-silica lava that flows readily.

Describe the volcanic features found on Venus and Mars. Do volcanic features on these planets resemble volcanic features on Earth? Explain.

Venus has about 150 large volcanoes measuring between 100 and 600 kilometers across and about half a kilometer high. Like Earth, Venus has volcanic mountains and other features that are probably made of thin, runny lava. On Mars, there are large shield volcanoes similar to those on Venus and Earth, as well as cone-shaped volcanoes and lava flows. Mars also has lava plains that resemble the lava flows on the moon.

Describe some of the hazards posed by volcanoes.

Volcanic ash can bury entire towns, damage crops, and clog car engines. If it becomes wet, the heavy ash can cause roofs to collapse. If a jet sucks ash into its engine, the engine may stop. Eruptions can also cause landslides and avalanches of mud, melted snow, and rock.