Page 20 - Curriculum Visions Dynamic Book. To close the book, close the tab.

Gabbro
G
Gabbro
An alkaline igneous rock, typically showing dark-colored crystals; it is made of the
same minerals as basalt, but has large crystals because it solidified slowly deep underground (see: Augite and Hornblende).
Although gabbro makes up a thick layer below the basalt that covers the ocean floor, it is
rare to find gabbro on land. Outcrops of gabbro mainly occur where parts of ancient ocean plates have buckled upward and become mountains.
Gas
One of the three states of matter; the other two are liquid and solid. In the case of volcanic activity gases are connected to places where magma is close to the surface. In these places liquids find their way to the surface,
often as volcanic eruptions. These liquids have substances in them that are only liquid under great pressure. When these substances reach the surface and are not under so much pressure, they change into gases. Sulfur dioxide and hydrogen sulfide are two of the gases found in eruptions and also in fumaroles. Hydrogen sulfide smells of rotten eggs, while sulfur dioxide is a brown gas. Many other gases are also released, but they are colorless and have no smell. Carbon dioxide and oxygen are two such gases. (See also: Glowing avalanche.)
 Geyser—Old Faithful Geyser, Yellowstone National Park.
20
Geyser
Hot springs that send powerful jets of steam and water into the air from time to time. They are found in places where hot volcanic rocks are quite close to the surface. Many geysers are found in the same areas as volcanoes, or where volcanoes were once active below the surface and where magma chambers still contain hot rocks.
Geysers are not the only signs that there are hot rocks near the surface. Hot springs and mud pools are in fact much more common than geysers. Sometimes, when there is little water available, puffs of steam, or gases with breathtaking sulfurous smells, are the only signs. They are called fumaroles.
Magma chambers are also places where great chemical changes occur. As steam, gases, and water move through the rock, they dissolve many of the minerals from the rock, so the geysers are far from being pure water. Rather, they contain a wealth of dissolved minerals.
As the hot, mineral-laden water comes to the surface, it cools.
Because cool water can hold less dissolved material than hot water, the minerals are deposited on the land around the geyser. The minerals build up into geyser cones.
Yellowstone National Park in Wyoming is one of the most famous areas of hot springs and geysers in the world. The magma that heats the water lies below the park. The volcano that was fed by the magma last had a major eruption 600,000 years ago, but minor eruptions have occurred since.
The rocks below the surface remain hot; and when cool water from the surface seeps down to them, they heat it up and cause geysers.
The geysers at Yellowstone lie inside a caldera 45km by 75km in size. The geysers now rise from the floor of the caldera. Old Faithful, the most famous of the geysers, gushes upward, around 35m to 50m high, every 40 to 80 minutes, although most geysers are not as regular as this.