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a data base for resource management decisions on Federal mineral lands. The l:100,000-scale digital cartographic data base combines the heretofore elusive qualities of sufficient detail, adequate content, and nationwide coverage that will allow, and perhaps foster, the widespread use of spatial analysis methods. Digital dashboard road maps and automated yellow pages based on the information in this data base are two futuristic concepts that could become a reality.

A synergistic effect will be realized through the combination of the l:100,000-scale data base with digital remote sensing data. The new generation of higher resolution, multispectral remote sensing satellites (Landsat 4 Thematic Mapper, SPOT, and others) are providing detailed data about the Earth's surface. The cartographic data could provide accurate geometric control for the remote sensing data. Networks of linear features (for example, major highways) extant in both sets could allow for better fit of remote sensing data to a cartographic base than is now possible through the use of isolated control tie points. The digital merging of these two types of data could allow new methods of imagery analysis

to be developed. Conversely, if the resolution of the remote sensing data is adequate, direct digital update of features in the cartographic data base may be possible.

SUMMARY

The Geological Survey is beginning a program to create a digital cartographic data base containing transportation and hydrographic features from its l:100,000-scale maps by the end of the decade. The Bureau of the Census is cooperating in the development of this data base and will enhance it through the addition of street names and census geocodes. The existence of this data base will enable the widespread use of geographic information systems for a host of resource-management, areaanalysis, and planning activities. Combined with remotely sensed digital data, our ability to study and monitor the Earth's surface will be improved. This data base will not only meet the immediate (1990) needs of the Federal community, but it may well serve as the catalyst for the widespread use of geographic information systems technology in the United States.

Disintegration of the Lower Reach of Columbia Glacier, Alaska, Now Under Way

By Mark F. Meier

The terminus of Columbia Glacier as viewed from Heather Island on August 14, 1984. Note the immense grounded icebergs in the foreground. Mount Columbia (left) and Mount Witherspoon (right) are visible in the background. (Photograph by Mark F. Meier, Water Resources Division, U.S. Geological Survey.)

The Trans-Alaska Pipeline carries oil from the North Slope of Alaska, where ice problems abound, to Valdez, described as "our northernmost ice-free port." Here the oil is loaded on tankships for delivery to the lower 48 States. At the time the pipeline terminal was built, ice in the shipping lanes of Valdez Arm was encountered rarely and was not considered to be a problem. Now, however, icebergs are seen frequently in Valdez Arm, and, occasionally, tankships have to be diverted or delayed because of ice. These delays can be expensive; oil storage capacity at the terminal is limited, and stoppage of the flow in the pipeline or pumping of the wells can have serious economic consequences. And the iceberg problem is likely to get worse before it gets better.

Why is this happening? It is because the nearby Columbia Glacier is beginning to disintegrate, causing a large increase in the breaking off (calving) of icebergs. This disintegration was, in fact, predicted by U.S. Geological Survey glaciologists in 1980. The prediction followed the development,

also by Geological Survey glaciologists,

of an understanding of why glaciers that end in the sea behave the way they do.

Most glaciers that end on land advance or retreat slowly in response to fluctuations in climate. Glaciers that end in the sea also may advance or retreat slowly, but sometimes they make extremely rapid and long-continued retreats; for instance, Muir Glacier in Glacier Bay has retreated 25 miles since being mapped by a Geological Survey glaciologist in 1892, while neighboring glaciers have remained stable or even advanced. Even more remarkable, the composite Guyot-Yahtse-Tyndall Glacier, which terminated on the continental shelf of the Gulf of Alaska at the turn of the century, has now retreated 29 miles, creating the present-day Icy Bay, yet the glaciers on either side have remained virtually unchanged.

The cause of these unusual rapid retreats is now known: It is because the speed at which the glacier releases (calves) icebergs depends on the water depth at the terminus (end) of the glacier. The speed of calving is high when a glacier terminates in deep water

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and is low when a glacier terminates in shallow water. When a glacier ends in shallow water, the rate of ice flow to the terminus can match the rate of ice discharge from the terminus; the glacier is stable. On the other hand, when a glacier ends in deep water, the rate of discharge of icebergs is very high and cannot be matched by ice flow; the glacier is unstable and retreats very rapidly and irreversibly until it again ends in shallow water.

Columbia Glacier, which terminates in the waters of Prince William Sound near Valdez, Alaska, had been stable since first studied in 1899. Survey glaciologists, however, realized in the mid-1970's that it could make a drastic retreat and that the ensuing increase in iceberg discharge might pose a problem to the shipping of oil from the Valdez terminus of the Trans-Alaska Pipeline. By 1980, iceberg calving relations had been quantified, computer models of the glacier's dynamics had been developed, and a prediction had been issued (fig. 1). This prediction stated that disintegration of the lower reach would, in fact, begin in the next few years and that the iceberg discharge would increase to more than six times the 1977 to 1980 level.

Disintegration of Columbia Glacier is now underway. Since 1980, recession, thinning, and iceberg discharge have been accelerating. Never before have scientists been able to observe the beginning of instability and drastic retreat, and observations of this glacier are adding much new information, some of which is surprising and unanticipated; for instance,

• Ice velocity, which had averaged 15

to 23 feet per day at the terminus
between 1977 and 1978, rose in
1983 and averaged more than 50
feet per day during winter
1983-84.

• Iceberg calving, which had averaged

about 3 million tons per day from 1977 to 1981 and was almost zero in winter, rose to 10 million tons per day during winter 1983-84 and continues at a high rate.

• The rate of retreat has accelerated,

from an average of 130 feet per
year from 1976 to 1981 to 600 feet
per year from 1981 to 1983 to
1,560 feet from 1983 to 1984,
referenced to the July 1 position
each year (fig. 2). From July to mid-
August 1984, retreat measured 16
feet per day averaged over the
width; in the center, it was 50 feet

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per day in spite of a forward ice flow of 39 feet per day, so the calving in midglacier was averaging 89 lineal feet of glacier ice removed each day. As the glacier is more than 1,000 feet thick at the terminus, this is a huge volume of ice discharged each day. The thickness of the lower reach of the glacier decreased 85 feet on the average between 1974 and 1981. During the next 2 years, September 1, 1981, to September 1, 1983, it decreased an additional 100 feet, and the rate of thinning continues to increase. The ice reserves of this glacier are being depleted in an unsuccessful attempt

to make up for the ever-increasing

loss by iceberg calving. Perhaps most unusual was the fact

that during February and March 1984, a portion of the glacier "surged" out in front of the rest of the terminus as a floating tongue, and other parts of the terminus appeared to be in a near-floating condition. This situation had not been anticipated, but this is the first time that the beginning of calving disintegration had been subject to close scrutiny by scientists. With the disintegration of the Columbia Glacier now underway, Geological Survey scientists are monitoring the rate of iceberg discharge with great care. This monitoring is essential because serious economic consequences could result from appreciable delays in the delivery of oil from the Trans-Alaska Pipeline.

Figure 2. Longitudinal section of the terminus of Columbia Glacier, as of August 1984; the 1974 and the 198 1 profiles also are shown. Although the terminus of the glacier has retreated into water more than 900 feet deep, the ice is not floating. Also, large icebergs are grounded against the moraine shoal, trapping other floating ice blocks and delaying their release to navigable waters.

Mineral-Resource Research at the U.S. Geological Survey— Linking Past Data to Current and Future Needs

By John H. DeYoung, Jr.

Introduction

Minerals are an essential component of our modern industrial society. The important role that minerals play in our daily lives usually is taken for granted—from the moment we turn on the water faucet in the morning until we turn off the light at night. We use automobiles, refrigerators, telephones, and other necessities of our modern lifestyle without thinking of the complex processes by which raw materials are acquired and these items are made.

These mineral raw materials have been provided in bountiful fashion from the apparent cornucopia of the Earth's resources. In the early days of our Nation's history, deposits of metals and other mineral materials were found in close proximity to the population that used those materials and settlements often were established in areas undertaking mineral development operations. The westward movement of the population brought new mineral discoveries, and, in some cases, the mineral discoveries spurred more movement to the West. As domestic deposits of some minerals were depleted, the United States turned to international trade to satisfy its needs for minerals.

Today, we are dependent, to a significant extent, on foreign sources for at least 20 important mineral commodities—from manganese, an essential ingredient in steelmaking, to cobalt, an indispensable component of hightemperature alloys such as those used in jet engines. Proposals to lessen U.S. mineral-import dependence rely upon solutions that include alternative sources of domestic production, finding new deposits abroad to increase competition in foreign markets, research on substitute materials, and investing in stockpiles to lessen the effect of our import dependence in crisis situations.

Whether or not our mineral raw material needs are satisfied from domestic or foreign sources, the process that moves minerals from the concep

tually dimensionless point of undiscovered resources at the tip of the cornucopia to the reality of production that we see issuing forth from the world's mines, quarries, pits, and wells involves scientific research. This scientific inquiry reaches into the physical properties that characterize the Earth's resources, the geologic processes that are responsible for concentrating the rare occurrences of mineral wealth that we call ore deposits, and the ways to explore successfully for these deposits. Continued discovery of mineral deposits has warded off the exhaustion of mineral supplies predicted by some popular writers, who reasoned that the depletion of nonrenewable resources from a fixed number of deposits permited the calculation of a day of reckoning for mineral resources. In the past, however, carefully reasoned estimates of remaining resources of coal, oil, copper, or other commodities later proved to be conservative because of new discoveries.

The discovery stage in the mineral supply process is the result of inquiry driven by the immediate goal of providing information to use in solving today's problems. This research usually draws upon knowledge accumulated from past scientific investigations. In addition, a plan for research can recognize that solutions to future mineral supply problems will be made with today's basic research results and thus can anticipate potential problems. With such a research plan, we shall be ready to solve these problems or to avoid them entirely.

Highlights of fiscal year 1984 mineralresource research at the U.S. Geological Survey include examples of studies directed towards immediate problems, accumulation and organization of data from past investigations, and studies of basic research questions that will build the analytical tools for tomorrow's

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