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ALASKA
Figure 65.--Sketch map of Cook Inlet region, showing
major Qua ternary volcanoes (stars) and approximate
locations of lakes where bottom-sediment cores were
taken: I, Bear Lake; 2, Big River Lakes; 3, Upper
Satematof Lake; 4, Hidden Lake; and 5, Hideeway
Lake.
All the lakes cored thus far from the region con-
tain two or more tephra layers. The shallower lakes
generally preserve only the thicker tephra layers;
many thin tephra layers are destroyed or obscured by
sediment mixing due to wave action, bottom currents,
and burrowing organisms. The deeper lakes in the
region contain the most complete tephra records. A
core from Hidden Lake (fig. 65, no. 4) id the central
Kenai Peninsula (llymer and Sims, 19821, for example,
contains at least 10 tephre layers; an additional 7 thin
light-colored Iaminae that may aIso be tephra have not
yet been examined microscopically. Pow radiocarbon
ages from the Hidden Lakc core permit preliminary
dating of individual tephra layers by extrapolation of
sedimentation rates between dated core segments.
This procedure suggests that ash falls occurred on the
central Kenai Peninsula about 300, 2,880, 3,900, 6,560,
8,210, 8,370, 11,360, 13,700, 14,500, and 14,700 years
B.P. The last two dates are pwticularly speculative
because no radiocarbon data are available from the
lowermost part of the core owing to low organic con-
tent, although the sedimentary structures and compo-
sition in that part of the aore suggest a rapid sedi-
mentation rate.
No single Iake, however, can provide a complete
record of the ash falh for the entire region because
ash plumes commonly pass over only parts of south-
cenbal Alaska. Meny ash clouds from volcanic erup-
tions on the southern Alaska Peninsula and the
AIeutinn Islands me swept southeastward Into the Gulf
of Alaska and entirely bypass the Cook Wet region.
Ash falls from volcanoes dong the west side of Cook
Inlet (such as Mount St. Augusthe, Mount Iliamna,
Mount Redoubt, and Mount Spurr) are most likely to be
represented in the region's lakes (fig. 65), although
volcanic ash from more distant sources may aIso occaslonally
fall on the Cook Wet region.
Pollen analysis of the sediment core from Hidden
Me permits the reconstruction of a regional vegetation
histary spanning more than 14,000 years (Ager and
Sims, 1981b; Ager, 1983), the oldest continuous late
Quaternary pallen record yet obtained from anywhere
in south-central or southeastern Alaska. The earliest
recorded vegetation to appear was an herbshrub tundra
that developed soon after glacial ice retreated
from the western Hidden Lake area more than 14,000
years B.P. By about 13,700 years B.P., mesic shm$
tundra developed that included dwarf birch (Betula
- naaa), ericales (Ericaceae, Em etrum ni urnwinow
(m spp.). Poplar P--+
Populus spp. began to
spread into the area by about 10,400 years B.P. The
regional vegetation soon developed into a mosaic of
shrub tundra communities Lnterspersed with thickets of
willow and scattered stands of poplar. Alder shrubs
(m spp.) spread rapidly in the region between about
10,000 and 9,500 years 8.P. The first conifers to
Invade the region were spruce (Picea), which appeared
abruptly at Hidden Lake aboutm-8,000 years B.P.
These first invading spruce were probably white spruce
(Plcea glauca), which apparently spread very rapidly
( E x 0.3-0.4 kmlyr) southward from the Tanane
Valley in interior Alaska (Ager, 1975) through the
mountain passes of the Alaska Range (Ager and Sims,
1981a) and the Talkeetna and Chugach Mountains.
Previous investigations of pollen profiles from
peat cores collected along the south and east coast of
the Kensi Peninsula and in Prince William Sound
(Heusser, 1960) suggest that coastal forests consisting
primariLy of Sitka spruce (picea sitchensis), smaller
amounts of mountain hernla~~su~a mertonsiana),
and some western hemieck (z. heterophyUa) reached
those areas from the east during mlddle Holocene
time. Pollen of Picea glauca and & sitchensis cannot
yet be differentiated, and so It is unclear when
elements of the coastal forest reached the east edge
of Hidden take on the west flank of the Kenai Mountains.
The first appearance of traces of pollen of
mountain hemlock in the Ridden Lake core at bout
5,000-4,000 yews B.P. may indicate that at least some
elements of the coastal Sitka spruce-hemlock forest
reached the Bidden Lake area about that time.
Other cores of lacustrine sediment were obtained
neat Kenai on the Kenai Peninsula, near Anchorage in
upper Cook Inlet, and in the vicinity of Mount Redoubt
on the west side of Cmk Inlet (fig. 65) in March 1981
by T. A. Ager, James Reihle, and Susan Battsch-
Winkler. Preliminary anasis of these cores reve&
thmt polIen of a occurs in the lowest pllenbearing
sediment of the cow. This observation
suggests that the maximum age of the cores is probably
less than 10,000 yews, on the bask of the pollen
zonation and chronology established for the Hidden
Lake core.