About 7,000 years ago two major tephra-falls blanketed the
Pacific Northwest in volcanic ash. These two tephra-falls, identified
as the Llao and climatic tephra-falls, were a part of the eruptive
events that led up to the collapse of Mount Mazama to form Crater Lake
in the southern Oregon Cascades.
The tephra-falls occurred about 200
years apart at around 7,000 years B.P. and 6,800 years B.P. for the
Llao and climatic eruptions respectively.
The effects of the tephra-falls on the flora, fauna, and people of the period have been
characterized by different researchers as ranging from minimal to
catastrophic.
In an attempt to better understand the affects of these two
events on the flora, fauna, and people, a model is presented to help
organize the various lines of research into a coherent whole and to
suggest profitable areas of research which have not yet been completed.
The model is based on ecological and anthropological theory with a
strong reliance on analogy with modern ecosystems and volcanic hazards
research.
The model makes use of the ecosystem concept as the framework
for the interaction of the abiotic, or nonliving habitat, with the
biotic, or living system. The biotic organisms are adapted to the
characteristics of the abiotic habitat and in many respects the
composition, frequencies, and distributions of biotic organisms are
determined by their tolorance levels to these characteristics. Tephra-falls act as environmental disturbances which change the abiotic
habitat of the ecosystem. Therefore, any changes caused by such
a disturbance in the abiotic characteristics that are not optimal or
are outside of the tolorance limits of the biotic (flora and fauna)
components should cause changes in the composition, distribution, and
frequency of organisms within the ecosystem. The changes brought
about by the tephra-falls may be described by successional and
evolutionary processes through analysis of pollen and faunal remains,
population demography as described by mortality profiles, and research
into the reaction of specific flora and fauna within adaptational
types to the properties of tephra-falls and the tephra as a soil
body.
The state factors used to describe the abiotic component of the
ecosystem are: time, distribution, material properties, climate, and
geomorphology. The state factor of time involves the determination
of the occurrence in time of the event(s), the duration of the event(s),
the season of occurrence of the event(s), and the residence time of
tephra in the ecosystem. This state factor is used to define the
specific point in time and duration of the effects of the tephra-fall(s) for individual ecosystems. The state factor of distribution
describes the aerial extent and thickness of the air-fall deposits.
This state factor determines the extent of the initial disturbance.
The state factor of climate describes the specific components of
rainfall, wind, and temperature which control ecosystem composition
and development, and the changes to the climate which may have occurred
due to volcanic aerosols associated with the eruption. The state
factor of geomorphology describes the location of tephra and nontephra
bodies across the landscape and through time as the tephra is reworked
by wind, water, and gravity from the initial air-fall positions. The
determination of the long term distribution of the tephra is important
in determining post-event influences on ecosystems as described by
the material properties of the tephra.
It is argued that most people were not greatly harmed by the
Mazama tephra-fall events themselves, but instead may have been
greatly affected by a loss of food resources during and after the
events. Changes in food resource availability and exploitation
locations due to the tephra-falls may have resulted in changes in
both settlement and subsistence activities. Changes in settlement and
subsistence activities may be seen in a corresponding change in
differential frequencies of functional tool types across space and
time. The kind and amount of expected changes in settlement and
subsistence systems are linked to distance from the source of the
tephra, the stability and compostion of pre-disturbance ecosystems,
the types and intensity of resource exploitation, and the amount of
variability in subsistence and settlement traits which were available
to the sociocultural system. / Graduation date: 1988
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33997 |
| Date | 28 May 1987 |
| Creators | Matz, Stephan E. |
| Contributors | Brauner, David R. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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