YEAR IN REVIEW 1997: EARTH-AND-SPACE-SCIENCES

GEOPHYSICS Seismic activity was high during recent months. One of the largest earthquakes occurred on Oct. 9, 1995, near the coast of Jalisco, Mex., and left 19 persons dead, more than 100 injured, and at least 1,000 homeless, mostly in Colima. The quake was felt in Mexico City and by persons in high-rise buildings as far away as Houston and Dallas, Texas, and in Oklahoma City, Okla. A tsunami estimated to have reached a maximum height of 5 m (17 ft) was generated. It was registered throughout the Pacific Basin, in the Marquesas Islands, the Hawaiian Islands, French Polynesia, Western Samoa, and even Southport, Australia, where its peak-to-trough amplitude was four centimetres. Five shocks occurred with magnitudes of 7.9: on Dec. 3, 1995, in the Kuril Islands; on Feb. 17, 1996, in Indonesia; on June 10 in the Andreanof Islands off the coast of Alaska; on June 11 near the Philippine island of Samar; and on June 17 in the Flores Sea near Indonesia. Although the quake in the Andreanofs caused a tsunami that was registered in Hawaii, Crescent City, Calif., and Port Angeles, Wash., only the earthquake of February 17 caused fatalities and appreciable damage. It left 108 dead, 423 injured, and 58 missing and destroyed or seriously damaged more than 5,000 homes, some owing to a tsunami. It is not always the most powerful earthquakes that are the most destructive. The most devastating earthquake of 1996 occurred on February 3, in Yunnan province, China, where at least 251 people were killed and more than 4,000 were injured. It was estimated that 329,000 homes were destroyed throughout northwestern Yunnan and that one million people were left homeless. The magnitude of the shock was 6.6. Another shock on Oct. 6, 1995, in southern Sumatra, magnitude 6.7, killed 84, injured more than 1,800, damaged more than 17,000 homes, and left 65,000 homeless. Two smaller earthquakes, of magnitude 5.9 each, caused fatalities. The first, on March 28 in Ecuador, killed at least 19 and injured 58; the second occurred on May 3 in western Nei mongol, China, and left 18 dead and 300 injured. A total of 15 earthquakes of magnitude 7.0 or greater occurred. February was exceptionally active, experiencing eight shocks with magnitudes between 6.0 and 6.9 and four of magnitude 7.0 or higher. The most notable volcanic activity was the continuing series of eruptions of the Soufrire Hills volcano on Montserrat in the West Indies, which began on July 18, 1995. It was the first volcanic activity that was recorded on the island since it was visited by Columbus in 1493. The volcano began by producing clouds of ash that slowly increased in duration. New vents opened on July 18 and July 30. Low-level activity continued until an ash explosion formed a third vent on August 20, when some 5,000 people were evacuated. On August 27 there was a magma eruption, producing a lava flow and an ash cloud that coated the nearby city of Plymouth and blotted out the light for 25 minutes. On the next day ejecta were hurled as far as three kilometres (two miles) from the summit. This time 6,000 residents took refuge at the northern end of this the island, which is only 13 km (8 mi) in length. Twice afterward the situation became ominous to the degree that three other evacuations took place, in November 1995, April 1996, and September 1996. While seismic activity and other indicators have been effective in predicting eruptions in many instances, additional methods are needed. During the year a geochemist, Tobias Fischer, at Arizona State University found one that appeared to have great promise. Volcanologists had determined that the mechanics of volcanism result in a predictable chain of events. The molten magma gives off a volatile mix of gases, containing carbon, hydrochloric acid, and sulfur dioxide. These escape under great pressure, forcing out rainwater in the form of steam. When the tubes or fissures become clogged owing to the accretion of minerals or by cooling of the surface rock, pressure builds within them until it is released with explosive force. In June 1992 Fischer began monitoring the content of the gases escaping from the active Galeras volcano in Colombia. He found definite changes in gas temperature and the percentages of the various chemicals before an eruption. In the week prior to the latest large event, the temperature of the surface rock dropped from 750 to just over 400 C, and the amount of the very soluble hydrogen chloride dropped to one-thirtieth of the mixture, while that of the insoluble carbon dioxide remained unchanged. Fischer reasoned that water was not expelled because the channels were blocked and the water consequently seeped into the rocks, dissolving the salt. This increase in salt indicated blocked tubes, which in turn indicated a pressure buildup and an imminent eruption. According to the long-accepted theory of isostasy, mountains float on the denser mantle, similar to icebergs in the ocean. The mass of the mountain below the surface of the ground, extending downward as much as 60 km (37 mi), is greater than that of the visible portion. This is apparently not so for the Sierra Nevada mountains, however, according to Stephen Parks and his team, who began working on the Southern Sierra Continental Dynamics project in 1992. Using extensive seismic refraction surveys, they determined the thickness to the mantle beneath the mountains to be only about five kilometres (three miles). Furthermore, electrical resistivity surveys showed that there were areas of partially molten rock beneath the crust. This indicated to the investigators that the mountain roots were being melted and were less than half the size they had been 15 million-20 million years ago. Thus, in theory, the Sierra Nevada chain, which contains Mt. Whitney, the highest peak in the contiguous U.S., should be sinking rather than rising. Further research efforts would be designed to map the magma, date deep cores, and attempt to determine whether the Sierras were higher in the past. Another study of geodynamics produced rather startling results. The most widely accepted theory of plate tectonics supposes that the plates float on the mantle or at least move independently of it. Recently, however, researchers from the Carnegie Institution of Washington, D.C., and the University of So Paulo, Brazil, found a fossil plume buried deep in the mantle beneath Paran flood basalt that has remained stationary with respect to the South American plate, which thus demonstrates that a portion of the mantle is moving with the plate and that the mantle and the continent have been coupled since the opening of the South Atlantic Ocean about 130 million years ago. (RUTLAGE J. BRAZEE) METEOROLOGY AND CLIMATE Aided by advanced numerical models, the scientific understanding of the atmosphere--and of the interactions between the ocean and atmosphere--and the ability to forecast large- and small-scale meteorologic and hydrologic phenomena on a variety of time scales have increased dramatically during the past two decades. Rapid technological advances have also increased the capability to collect and process vast amounts of atmospheric data. This knowledge and technology provide meteorologists and hydrologists with many research opportunities that are expected to lead to improved forecasts. Long-term outlooks for periods of as much as a year into the future are now possible. While such long-range predictions do not have the precision of tomorrow's forecast, they can provide useful planning information for such industries as utilities, agriculture, and water-supply management. One basis of seasonal prediction is the ocean-atmospheric interaction in the South Pacific Ocean. The research on this interaction has enabled the prediction of tropical sea-surface temperature variations for as long as a year. With this knowledge forecasters have been able to predict seasonal temperature and rainfall variations over North America. Increasingly sophisticated regional models of the atmosphere are being developed to bring these forecasts down to the regional scale. Global-scale climate changes based upon the possible consequences of increases in "greenhouse" gases in the atmosphere are being studied. These gases, which include carbon dioxide, can affect climate and weather by modifying the radiative characteristics of the atmosphere. As the accuracy of models of large-scale changes in the atmosphere increases and as computers become faster, research efforts will continue to improve medium-range (three-to-five-day) forecasts. That these efforts have paid dividends was demonstrated when the forecast models developed by the National Weather Service accurately predicted the superstorm of March 1993 five days in advance. Five-day forecasts in 1996 were as good as three-day forecasts were 15 years ago. Considerable research was also taking place in regard to short-term forecasts. Improved models of the atmosphere have resulted from the incorporation of sophisticated representations of physical processes, such as the effects of ocean temperature and topographic variation at the Earth's surface. Such research has led to rapid progress in "mesoscale" meteorology--the meteorology of severe local storms. Because short-term and long-term meteorology is global in scope, it has historically fostered international cooperation. Efforts were expected to continue in such areas as the exchange of real-time data, scientific collaboration, and technology transfer. One example was in the area of river forecasting and water management. The performance of recently implemented forecast systems (using U.S. river-forecasting techniques) during the extensive flooding in the summer of 1996 in China was widely praised. In spite of these improvements in forecasting, some of the most deadly meteorological menaces, such as tornadoes, lightning, and flash floods, still could not be forecast with total precision. In an effort to improve such forecasts, the U.S. deployed advanced observing instruments, such as Doppler radar, satellites, and telemetering observation systems, to provide real-time data in order to mitigate the loss of life from rapidly evolving small-scale meteorological events. Doppler radars can detect the speed and direction of wind as well as precipitation within developing storms. This allowed early detection of severe thunderstorms and tornadoes and also provided precipitation estimates important to forecasting of flooding. Geostationary satellites provided images of storm systems as frequently as every six minutes during severe weather situations. Automated surface-observing systems provided a significant increase in the number of observing sites, including many airports. New forecast capabilities could also benefit the economy. A new field of meteorological application was unfolding as industry learned to apply the improved weather products and services to the benefit of their companies. The future of meteorology thus seemed certain to be an expanding collaborative endeavour between federal and state governments, academia, and the private sector. (ELBERT W. FRIDAY, JR.) OCEANOGRAPHY Two distinctive features of research in oceanography during 1996 were the importance of new technology in carrying out observations and the evident necessity of observational programs extending over many years, not only for long-term monitoring but also for developing a conceptual background that would help researchers formulate new scientific questions. The Ocean Drilling Program (ODP) had its inception in an attempt, in 1961, to drill through the ocean floor to the Mohorovicic discontinuity separating the Earth's crust from the mantle beneath. This effort became the Deep Sea Drilling Program in 1968 and was transformed into the present ODP in 1984, when the drilling ship JOIDES Resolution was commissioned. When drilling was begun, the ideas of plate tectonics were in their infancy, and scientists' view of the events that shape the seafloor emphasized processes that occur over geologic time scales. But during the lifetime of the drilling programs, even more evidence has been found supporting the importance of sudden events. Several of these were observed in 1996. The ability to detect them and to put observers above them at sea while they were occurring was possible only because of advances in ocean technology during the past decade. In late February the U.S. Navy's Sound Surveillance System (SOSUS) detected seismic events near the northern Gorda Ridge about 350 km west of the coast of northern California (1 km = 0.62 mi). By early March scientists were at sea in the region sampling the water column--a plume of heated water 10 km across that rose 1,500 m off the seafloor (1 m = 3.28 ft). Further studies in April and June found microorganisms that demonstrated the ability to grow at temperatures as high as 90 C (194 F) but could not grow at normal ocean temperatures. Loihi Seamount is an underwater volcano about 30 km southeast of the island of Hawaii. A hydrothermal vent system at a depth of about 1,000 m previously capped the summit. Seismicity was intense there for a month beginning in mid-July. Again, scientists were able to take field observations during the event. The newly changed seafloor was mapped acoustically; volcanic glass fragments were recovered, using submersible vehicles; and plumes of hydrothermally altered water were observed. At the conclusion the summit vent system had collapsed into a broadened summit crater whose floor was 1,350 m deep. Continued volcanism at Loihi over thousands of years would ultimately build the summit upward to the ocean surface. In September, while the JOIDES Resolution was drilling into metal-rich deposits formed by an old and inactive hydrothermal vent system about 240 km west of Vancouver Island (British Columbia) and just a few kilometres from an active vent, two new vents were created. Repeated visits to this site were expected to provide a unique opportunity for scientists to learn how the particular collection of organisms that flourish only in the extreme conditions near the vent colonize a new site. The World Ocean Circulation Experiment (WOCE) began a global survey of the circulation of the world ocean in 1990. In the Atlantic, WOCE data based on analyses of the distribution of tritium in the water were beginning to give a consistent picture of the "age" of subsurface waters (the time elapsed since those waters participated in exchanges across the air-sea interface), a picture that would be important in refining estimates of such quantities as oxygen consumption by living organisms at different depths. Tritium is primarily a product of atmospheric nuclear weapons testing, and its distribution thus provides information about water motions since the 1960s. Chlorofluorocarbons have entered the oceans as by-products of industrial activity, primarily refrigeration and air-conditioning. The WOCE measurements of the chlorofluorocarbon distribution in the Pacific were completed in 1996; levels of those compounds were below detectability in the deep waters of the northern Pacific but were well above detectability in the deep waters of the southern Pacific and in deep northward-flowing Pacific currents. Most of the WOCE fieldwork was scheduled to be finished by the end of 1997. The project largely attained its goal of providing a basic global picture of the circulation of the ocean over a period of several years. An important part of that picture is the global pattern of heat transport and of water exchange between the air and the sea. One of the most important practical applications for this knowledge is climate prediction. Planning began for a global study of the coupled atmosphere-ocean climate system and its predictability on time scales of seasons to years. This Climate Variability and Predictability Program was scheduled to begin in 1998 and was to last for 15 years so that year-to-year variability could be understood adequately. The complexity and variability of seafloor and fluid environments greatly complicates efforts to understand the abundance and variability of marine populations. Even so, during 1996 technological developments originating in physical oceanography made possible an open ocean test of the hypothesis that in regions of the ocean where nutrients and light are available in abundance yet phytoplankton populations are lower than expected, it is a lack of iron that is the limiting factor. In work carried out in 1995 and reported in 1996, an area about 30 km on a side in the equatorial eastern Pacific was initially surveyed to check that temperature and salinity, as well as biological and chemical conditions, were uniform, so that the sinking of cold or salty water relative to adjacent cold or relatively fresh water would be minimal. A small part of this region, about eight kilometres on a side, was then seeded with iron (as acidic iron sulfate) mixed with the inert tracer sulfur hexafluoride previously used to study vertical diffusion rates in California coastal waters and in the central Atlantic. A freely drifting buoy that constantly radioed its satellite-derived geographic position to the ship was used to mark the centre of the seeded patch. The ship carried out continuous surveys through the seeded patch around the buoy, measuring dissolved iron, sulfur hexafluoride, nitrate, and chlorophyll over a 19-day period. Chlorophyll levels increased by as much as 27 times several days after the last addition of iron, which indicated phytoplankton growth, and nitrate levels were correspondingly depleted. (MYRL C. HENDERSHOTT) See also Business and Industry Review: Energy; Mining; Chronicle: Disasters; The Environment; Life Sciences. This article updates atmosphere; climate; dinosaur; Earth; Earth sciences; earthquake; geochronology; hydrosphere; ocean; plate tectonics; river; volcano.