Geothermal energy

Another alternate energy resource is the heat from the Earth’s interior. The surface expression of this energy is manifested in volcanoes, fumaroles, steam geysers, hot springs, and boiling mud pools. Global heat-flow maps constructed from geophysical data show that the zones of highest heat flow occur along the active plate boundaries. There is, in effect, a close association between geothermal energy sources and volcanically active regions.

A variety of applications have been developed for geothermal energy. For example, public buildings, residential dwellings, and greenhouses in such areas as Reykjavík, Iceland, are heated with water pumped from hot springs and geothermal wells. Hot water from such sources also is used for heating soil to increase crop production (e.g., in Oregon) and for seasoning lumber (e.g., in parts of New Zealand). The most significant application of geothermal energy, however, is the generation of electricity. The first geothermal power station began operation in Larderello, Italy, in the early 1900s. Since then similar facilities have been built in various countries, including Iceland, Japan, Mexico, New Zealand, Turkey, the Tibet Autonomous Region of China, and the United States. In most cases turbines are driven with steam separated from superheated water tapped from underground geothermal reservoirs and geysers.

Mineral deposits

As mentioned above, the distribution of commercially significant mineral deposits, the economic factors associated with their recovery, and the estimates of available reserves constitute the basic concerns of economic geologists. Because continued industrial development is heavily dependent on mineral resources, their work is crucial to modern society.

It has long been known that certain periods of Earth history were especially favourable for the concentration of specific types of minerals. Copper, zinc, nickel, and gold are important in Archean rocks; magnetite and hematite are concentrated in early Proterozoic banded-iron formations; and there are economic Proterozoic uranium reserves in conglomerates. These mineral deposits and a variety of others that developed throughout the Phanerozoic Eon can be related to specific types of plate-tectonic environments. Among the latter are copper, lead, and zinc in intracontinental rifts. An interesting discovery has been the remarkable concentrations of gold, iron, zinc, and copper in brine pools and sulfide-rich muds in the Red Sea and in the Salton Sea in southern California. In many countries copper, nickel, and chromium deposits occur in ophiolite complexes obducted onto the continents from the ocean floor; porphyry copper and molybdenum deposits are found in association with granodioritic intrusions; and tungsten and tin deposits occur in many granites. The correlation of these associations and distributions with periods of Earth history, on the one hand, and plate-tectonic settings, on the other, have enabled regional metallogenetic provinces to be defined, which have proved helpful in the search for ore deposits.

During the 20th century the exploitation of mineral deposits was so intense that serious depletion of many resources was predicted. Mercury reserves, for example, are particularly low. To deal with this problem, it has become necessary to mine deposits having smaller and smaller workable grades, a trend well illustrated by the copper mining industry, which now extracts copper from rocks with grades as low as 0.2 percent.

Investigators have discovered a major potential metallic source on the deep ocean floor, where there are large concentrations of manganese-rich nodules along with minor amounts of copper, nickel, and cobalt. Such concentrations are especially abundant in three sections of the Pacific Ocean—the area near Hawaii, that northeast of New Zealand, and that west of Central America.