Trivia Junction

A Compendium of trivia I find interesting
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The earth is like a balloon

When the pressure inside a balloon is slowly diminished, the surface of the balloon begins to shrivel. As our civilization extracts oil, gas and other minerals from the interior of the Earth and volcanoes emit lava and gases, could there be some deformation of the surface of the Earth causing earthquakes and warming of the ocean?

Even though the deepest mines extend less than two miles into the ground and the deepest drill holes only reach about eight miles, the exploitation of our planet's resources considerably alters its surface. The most significant change is subsidence – the decrease in elevation of the land surface resulting from the removal of water, oil and gas and the collapse of underground mines.

Subsidence is a worldwide problem. It damages roads, buildings, canals, levees and other structures. It has also led to flooding in coastal areas that were originally above high-tide levels. Not all of the land movement is vertical. Horizontal shifts lead to cracks in the surface, which can erode to form large fissures.

More than 80 percent of the subsidence in the U.S. results from the removal of ground water, according to a report by the U.S. Geological Survey. For example, some areas of California's San Joaquin Valley have dropped 30 feet in 75 years. In aquifers containing layers of silt and clay, reduced water pressure can cause permanent compaction of soils and loss of water storage capacity.

Geologists have shown that natural or artificial changes in groundwater, tides, snow load or other alterations of stress on a fault can cause earthquakes. Large earthquakes can sometimes trigger eruptions in volcanoes up to about 500 miles away. However, overall the number of earthquakes and volcanic eruptions do not appear to be increasing. A link between land subsidence and ocean temperatures is also unlikely.

Volcanic activity alters the landscape locally, but it does not shrink the Earth's surface. The belching of volcanoes is quite different from the release of air from a balloon. As magma works its way toward the surface, the pressure on it drops. Consequently, the rapid expansion of water in magma to form a gas can propel molten rock into the air.

The center of Earth is not suffering a net loss of material, because rock and water return to the depths at subduction zones, places where regions of the Earth's crust plunge beneath one another. The heat that brings magma to the surface is also continually being generated by the decay of radioactive elements deep within Earth.

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