EARTH SCIENCES - Notable Research and Discoveries Part 5

earth ScienceS Molokini, a volcanic crater that forms a crescent-shaped island near Maui, Hawaii (Ron Chapple/Getty Images) steady, entrenched in the mantle, and the plate will move past it. Plates move slowly—in a range of one to six inches (2.5–15 cm) a year—but over millions of years, this movement is significant. Wilson’s theory suggested that the chain of Hawaiian islands were formed from this volcanic activity in a manner that reflects the movement of the plate. As the plate lingers over the hot spot, the volcanic activity builds a sea-mount, which gradually rises above the surface to create an island. After some period of time, as the plate moves on, another island in the chain forms, slightly behind the earlier island. Wilson published his theory in a report, “A Possible Origin of the Hawaiian Islands,” in a 1963 issue of the Canadian Journal of Physics. Kilauea is a highly active volcano located on the island of Hawaii (the Big Island). According to Wilson’s theory, the islands farthest from the current hot spot should be the oldest, since they were formed much earlier. Kauai, the most northwestern of the major islands in the chain, has rocks as old as 5 million years. This age contrasts with the Big Is-land—the most southeastern island—in which the oldest known rocks Volcanoes and hot Spots are less than 1 million years. The ages of the other islands also agree with the theory. Hawaiian volcanoes have been extremely important not only for volcanologists interested in hot spot theory, but also for legions of tour-ists and interested onlookers. Native islanders have been observing these volcanoes for many generations, and the British explorer Captain James Cook (1728–79) sighted the Hawaiian Islands in 1778. Written records of Kilauea began in 1790, showing that the volcano has been active for most of the past two centuries. In periods of high activity, such as during eruptions or when lava rises to a visible level, Kilauea draws a crowd. People such as Mark Twain (1835–1910), who visited the volcano in 1866, began writing about their experiences, and the rest of the world became aware of the fascinating spectacle. In 1916 the U.S. government established Hawaii Volcanoes National Park, which includes Kilauea on the Big Island. Hawaiian volcanoes continue to be As the plate moves over the hot spot, a series of volcanoes form. earth ScienceS the site of important observations and studies, as described in the fol-lowing sidebar. The Hawaiian Islands are the youngest in an extended chain of volcanic islands and undersea mountains (which do not quite reach the surface) stretching about 3,700 miles (5,920 km) across the Pacific Ocean. This chain is known as the Hawaiian-Emperor Seamounts. Ages of the rocks indicate a progressive increase from northwest to south-east—the oldest rocks in the northwestern islands and seamounts are millions of years older than those of the southeast, and the age increases the farther one moves to the northwest. This “trail” probably marks the track of the Pacific plate’s motion, but as shown in the following figure, Hawaiian Volcano observatory Scientists who are seeking active volcanoes have found Kilauea extremely attractive. Perret, the pioneering volca-nologist, visited Kilauea in 1911, and a year later the Massa-chusetts Institute of Technology professor Thomas A. Jaggar (1871–1953) began excavating along the rim of the Kilauea caldera. Jaggar and his team built a structure with a cel-lar that housed a seismometer, which he used to monitor the activity of the region. Money for this kind of geologi-cal research became easier to obtain after the disaster in Martinique in 1902 and the devastating earthquake in San Francisco in 1906, as people started to realize the value of volcanic and seismic research for society as well as science. The facility at Kilauea was the beginning of the Hawaiian Vol-cano Observatory. Today the Hawaiian Volcano Observatory is a component of the Volcano Hazards Program of the United States Geo-logical Survey (USGS). (The history and functions of USGS are outlined in a sidebar on page 10.) Researchers at the observatory study Kilauea and Mauna Loa, another volcano Volcanoes and hot Spots there is a sharp bend at about the middle of the chain that is not yet fully understood, corresponding to about 42 to 48 million years ago. The plate may have changed direction at this point, or the hot spot may not be stationary, as discussed below. Chemical analysis of the lava from the Hawaiian volcanoes yields clues about their origin. The lithosphere is about 50 miles (80 km) thick underneath the Hawaiian Islands, so if the magma is coming from underneath, it might be of a different chemical nature than the lava erupting from shallow mid-ocean ridges. In particular, geolo-gists have examined the ratio of isotopes of certain elements such as helium. on the Big Island. Mauna Loa is an active volcano, erupting more than 30 times since 1843, although it has not erupted since 1984. This massive shield volcano is the largest vol-cano on Earth—the mountain covers about half of the island and rises 2.4 miles (4 km) above sea level; its flanks extend another three miles (five km) beneath the surface of the ocean. It was the robust activity of these volcanoes that drew geologists to the site, and researchers at Hawaiian Volcano Observatory continue to monitor and track the volcanoes’ behavior, study the history of their eruptions by analyzing volcanic rocks in the area, and inform the public of the na-ture and potential hazards of these geological phenomena. In addition, because the Hawaiian volcanoes are not on a plate boundary, these volcanoes are important testing grounds for hot spot theories, although researchers did not know of this benefit when they initially set up the observatory. Sci-entific advances come about because of the persistence, intelligence, and, occasionally, good fortune of scientists. Researchers who explore the frontiers of knowledge never know in advance exactly where a project will take them or how rewarding it will be. 0 earth ScienceS Atoms of the same element may have a different number of neu-trons in their nucleus, resulting in different isotopes such as helium-3 (which has three particles in the nucleus, two protons and one neu-tron) and helium-4 (which has two protons and two neutrons in the ... - tailieumienphi.vn