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67°00" 66°00' 65°00 Track of the eye (15.5 miles in diameter) of
| | I T Hurricane Hugo as it passed over the Island
of Puerto Rico.

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material is unrecoverable. At other sites, material lost from the beach margins was deposited in the nearshore zone. Preliminary reconnaissance surveys show that about 10 percent of the stands of the shallow-water elkhorn coral in Vieques Passage were degraded considerably by Hugo. However, many deeper water coral colonies showed no visible impact. Hurricane Hugo left many Puerto Rican beaches, their valuable resources of sand, and their economic value as recreation sites more vulnerable to damage from future tropical storms.

Hurricane Hugo and the South Carolina Coast

By John W. Haines

S ullivans Island and Isle of Palms, two of the most heavily developed islands in the South Carolina coastal area, were positioned to receive the major impact of Hurricane Hugo. The storm made landfall in South Carolina early on the morning of September 22, 1989. Historically, Sullivans Island and Isle of Palms have been remarkably stable coastal areas. By comparing the positions of past shorelines, coastal researchers can show that Sullivans Island and the southern twothirds of Isle of Palms have grown slowly seaward during the last 50 years. The effort of USGS Coastal studies in the wake of Hurricane Hugo is focused on how the coastal effects of the storm relate to these long-term trends.

One of the special challenges of coastal research is that estimates of coastal erosion typically bracket periods of tens of years. Present shoreline positions are compared with past positions to determine the rate of coastal retreat or growth. These erosion estimates may or may not include the effects of a number of major storms, depending on how frequently an area has been affected by hurricanes or other coastal storms. Thus, best estimates of coastal land loss may mask the importance of these extreme, yet short-lived events. Coastal erosion in a particular area, therefore, may be due primarily to a few major storms, or it may reflect less extreme but more persistent processes. In addition, coastal response to hurricanes may depend on the presence of dunes and the width of the beach.

To gain a visual perspective on the coastal effects of Hurricane Hugo, the USGS and the National Ocean Survey made overflights of the South Carolina coast during the week of October 2, 1989. While aerial photography provides a means of rapidly accumulating data covering a wide area, the information

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effort resurveyed profiles previously obtained during a shoreline monitoring program initiated by the South Carolina Coastal Council. While such nearshore profiling provides only a local picture of coastal effects and is a slow data-collection process, it does show what has happened to the shore beneath the waterline and is critical in evaluating the redistribution of sediment. Study of the profile data for Sullivans Island confirmed that sediment was removed from dunes and the subaerial beach and that there was an associated accumulation of material in the nearshore area. The profiles, which show only minor changes in the position of the shoreline, are consistent with the shorelines derived from the aerial photography. Because of this relatively small change in the shoreline position, USGS researchers suggest that shoreline position alone may not be a representative measure of the impact of a major storm. While aerial photography shows only shoreline position and indicates a negligible response to the storm, the profile data clearly show substantial movement of sediment and modification of the beach-dune system. The coastal effects of Hurricane Hugo pose some interesting questions. Clearly large amounts of sand have been shifted offshore, but only when the ultimate fate of this sand is known will the long-term impact of Hugo be understood. If this sand is returned to the beach, the coastal system will have undergone little permanent change. Should the sand be transported further offshore, then, retrospectively, Hugo will be considered a major erosive event. The role of dunes in the coastal response to storms also remains unclear. While protecting inland structures, dunes may concentrate wave energy and enhance the offshore movement of sand. Here again, the ultimate fate of this sand is critical to understand long-term effects. Also, because many of the dune fields were removed during Hurricane Hugo, the response of the beach to subsequent storms may be greatly modified. Continued research is needed to determine the impact of hurricanes and other major storms on various coastal systems and the long-term impacts on coastal erosion and wetland environments. The infrequent and unpredictable nature of hurricanes pose special problems for the coastal geologist. A critical component in coastal studies will continue to be the availability of reliable prestorm data that provide a critical baseline for further research. The results from the studies of Hurricane Hugo will further efforts to understand and define the response of coastal systems to such devastating and unpredictable events of nature.

Redoubt Volcano, Alaska By Thomas P. Miller

ount Redoubt, an ice-mantled, 10, 197-foot-high stratovolcano located on the west side of Cook Inlet in Alaska, began its third major eruption this century with an explosive summit event at 10:14 a.m. AST, December 14, 1989, and recorded its last major explosive event on April 21, 1990. Although the volcano is located in remote Lake Clark National Park, 115 miles southwest of Anchorage, the eruption caused $50 to $100 million in damages— the second most costly eruption in North American history. The Alaska Volcano Observatory (AVO) monitored the eruption throughout its duration. The AVO is a cooperative effort that includes scientists from the USGS, the Geophysical Institute of the University of Alaska, and the Alaska Division of Geological and Geophysical Surveys. The AVO was established in 1988 to study and monitor Alaskan volcanoes and to provide volcanic hazard information to the public and private sectors. The principal AVO offices consist of a crisis center at the USGS office in Anchorage and a seismic interpretation center at the Geophysical Institute in Fairbanks. Personnel at both centers continuously monitored the volcano during the eruption and reported eruption information through a series of daily, and sometimes hourly, eruption updates. Tape-recorded messages available to the media and airlines were updated on a daily and situation basis. More than 30 scientists from other USGS centers, principally the Cascades Volcano Observatory, aided the Alaska-based personnel. A calldown procedure, part of a preexisting crisis response plan, was used extensively to alert airports, civil authorities, and the public through the news media. The existing seismic network around the volcano allowed AVO scientists to predict several major eruptive events, to inform appropriate agencies, the public, and the media when all major eruptions occurred, and to give estimates of relative eruption intensity. Overflights and helicopter-supported field studies provided critical information on the status and effects of the eruption. In spite of the bad weather and remoteness of the volcano, scientists successfully observed the volcano on more than 50 percent of the short winter days. Experimental seismic instruments recorded the occurrence and advance of mudflows and floods. A lightning detection

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system, emplaced around the volcano, con-
firmed the existence of ash versus steam in
the eruption plumes—a matter of great signif-
icance to the airline industry. Data on hypo-
thetical ash plume trajectories, plotted on the
basis of wind data supplied by the National
Weather Service, were released on a daily
basis. Gas from the eruption plume was sam-
pled to detect increases of sulfur dioxide that
could be a precursor of an impending erup-
tion. Sampling was conducted by using fixed-
wing aircraft beginning in March.

The AVO developed a color coded classification system to more concisely describe the level of concern about possible eruptive activity at Redoubt volcano. The readiness and activity associated with each of the four color codes are

Green: Volcano is in its normal dormant

State.

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