Introduction
The collection of nine papers that follows continue the series of U.S. Geological
Survey (USGS) investigative reports in Alaska under the broad umbrella of the geologic
sciences. The series presents new and sometimes preliminary findings that are of
interest to earth scientists in academia, government, and industry; to land and resource
managers; and to the general public. Reports presented in Geologic Studies in Alaska
cover a broad spectrum of topics from various parts of the State (fig. 1), serving to
emphasize the diversity of USGS efforts to meet the Nation's needs for earth-science
information in Alaska.
The papers in this volume are organized under the topics: Hazards, Geologic
Framework, Environment and Climate, and Resources. This organization is intended to
reflect the scope and objectives of USGS geologic programs currently active in Alaska.
The two Hazards studies discuss volcano-related topics in the seismically active southcentral
Alaska region. The first paper revisits the eruptive events of Redoubt Volcano
that occurred more than a decade ago and the subsequent development of the Alaska
Volcano Observatory (AVO). This treatise documents the historic impact of this eruption
and briefly summarizes the state of our knowledge of the other Cook Inlet, Alaska
Peninsula, and Aleutian Island volcanoes. Finally, it discusses the recent role that AVO
has had in seismic station installation and hazard assessment at volcanically active
sites throughout the world. The second paper discusses the eruptive history of Snowy
Mountain in the upper Alaska Peninsula. Because subsets of its 25-30 lava flows
erupted as packages in short episodes, calculation of the volcano's lifetime average
volumetric eruption rate is problematic. A portion of the cone was hydrothermally
weakened and collapsed in the late Holocene producing a 22-km2 debris avalanche.
Geologic Framework studies provide background information that is the scientific
basis for present and future earth science investigations. The first paper compares and
contrasts the Insular-Intermontane suture zone (IISZ) of southeast Alaska with the
Adria-Europe suture zone (AESZ) of Switzerland and Hungary. The study develops
the hypothesis that the zones have distinct differences as well as similarities and
neither is a simple lithotectonic terrane boundary. The second paper discusses the
relation among volcanic, glacial, and tectonic activity in the Cold Bay and False
Pass 1 :250,000-scale quadrangles on the Alaska Peninsula. During Pleistocene time,
continental-shelf glaciations and two massive volcanic centers were the dominant controls
over landscape development. The third paper gives detailed geologic information
for Paleozoic rocks within the Taylor Mountains D-1 quadrangle portion of the Holitna Lowland of southwestern Alaska. Because of the excellent preservation of megafossils,
these Silurian and Ordovician strata lend themselves to detailed statigraphic investigations.
Further, low thermal alteration indices of this area have made them a potential
target of petroleum exploration. The final report in this section discusses the development
of a new spectral enhancement approach for interpreting Multispectral Scanner
(MSS) and Thematic Mapper (TM) satellite images. This technique enhances the use
of remote sensing data in identifying geologic units in areas that have been poorly
investigated. This study used this technique to better define the distribution of a JMtu
(mafic, ultramafic, and sedimentary) unit and a PzZrqs (pelitic and quartzitic schist)
unit.
Environment and climate studies are the emphasis of two papers. One presents the
first radiocarbon-dated postglacial vegetation history of the Kenai Mountains of southcentral
Alaska. This reconstruction is the result of the analysis of pollen assemblages
and peat from sediments collected in Tern Lake and presents a minimum age for
deglaciation of these interior valleys at 9,31 0±200 yr B .P. Current vegetation, however,
developed within the past ca. 2,500 years. A second study discusses the cycling of
arsenic and cadmium in sub-arctic boreal forest ecosystems typical of interior Alaska
and defines the importance of various natural (geogenic) sources. The transport and
uptake into vegetation of these elements from soils developed from loess as well
as soils developed from the major rock units is presented. The bioaccumulation of
cadmium in willow (Salix sp.) and its potential consequence to the health of browsing
animals is discussed.
Papers related to resource issues comprise the topic of the final report. This paper
presents a brief statistical summary of the geochemistry of rock samples collected
in the east-central portion of the Eagle 1 :250,000-scale quadrangle. This study helps
define the rock unit source of both resource- and environmental-based chemical elements
of interest in the Fortymile mining district.
Two bibliographies at the end of the volume list reports covering Alaska earth
science topics in USGS publications during 1999 and reports about Alaska by USGS
authors in non-USGS publications during the same period.