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Kilauea Volcano, Hawaii : chronology and morphology of the surficial lava flow
|Title:||Kilauea Volcano, Hawaii : chronology and morphology of the surficial lava flow|
|Authors:||Holcomb, Robin Terry|
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|LC Subject Headings:||Lava--Hawaii--Kilauea Volcano|
|Citation:||Holcomb RT. 1981. Kilauea Volcano, Hawaii: chronology and morphology of the surficial lava flow.|
|Series:||(Open-file report ; 81-354)|
|Abstract:||Long-term variations in eruptive behavior occurred as Kilauea's present surface formed. These variations are revealed by geologic mapping, dating, and morphologic analysis of lava flows. The chronology is based on the secular variation of the geomagnetic field, reconstructed from paleomagnetic measurements of lava flows dated by 14 C. Key flows of unknown age are dated by comparison with the history of variation, and relative ages of other flows are determined from super position and vegetation development. Paleomagnetic dating precision varies with time and depends uponthe rate of secular variation and dispersion in the data. Typically, variation rates are about 4 degrees/century, and dispersions are about 4.5 deg. Principal sources of dispersion are imprecision in the 14 Cages (3.0 deg), local anomalies in the geomagnetic field (2.2 deg), and primary deformations of lava flows (1.7 deg). Dating precisions are about 100 years during the past 500 years and about 250 years during the preceding millenium. Precision should be increased to a few decades by reducing the dispersion, refining the history of variation, and adding paleomagnetic intensity to the record of variation. About 70 percent of Kilauea's surface is younger than 500 years, about 90 percent younger than 1000 years. A major hiatus in summit overflows occurred between about 1500 and 1000 years B.P. Much of Kilauea's present caldera dates from the 18th century, but an earlier caldera developed about 1500 years B.P. and later filled. |
Behavior of prehistoric eruptions is revealed by the morphology of their products. Eruptions are classified on the basis of duration, which is expressed in the degree of channelization achieved by lava flows. Lava flows are classified as aa, surface-fed pahoehoe, and tube-fed pahoehoe. Flow types and vent features are used to classify eruption assemblages corresponding to various eruption types. Type A eruptions last hours to days and leave open eruptive fissures and commonly a single lava flow consisting of surface-fed pahoehoe and aa.Type B eruptions last for days to weeks and produce pyroclastic central vents and multiple flows of surface-fed pahoehoe and aa. Type C eruptions last for months to years and produce small lava shields and many flows consisting of all three types. Type D eruptions persist for decades to centuries and produce large lava shields and flow assemblages dominated by tube-fed pahoehoe. Type E eruptions last for days to weeks, and their phreatomagmatic explosions may produce craters and sheets of pyroclastic material. This classification scheme was refined during detailed mapping (1:24,000) of the Mauna Ulu region and was then applied in mapping the entire volcano (1:50,000). Kilauea's past behavior has varied in space and time. The chief spatial variation is a decrease in typical eruption duration at increasing distances away from the summit magma reservoir. Other variations appear to be peculiar to particular localities. Changes have occurred over intervals of decades and centuries; some have been repeated and some may have occurred in evolutionary sequences. Two Type E eruptions large enough to produce extensive pyroclastic sheets have been followed by long intervals when most activity was confined to a summit caldera. Rift activity waxed as summit activity waned, and in one example the waxing sequence resembles an evolutionary progression: Rift eruptions were at first brief and widely separated in time and space but gradually became frequent along a restricted segment of the rift zone and culminated in sustained activity at one locality. The causes of long-term eruptive variation remain undetermined. Alternative phenomenological models are characterized as evolutionary, cyclical, and steady-state; these alternatives differ greatly in their implications on long-range forecasting.(Date: 1981).
|Description:||Thesis (Ph. D.)--Stanford University, 1981. Bibliography: leaves 311-321. With illustrations and maps.|
|Appears in Collections:||
The Geothermal Collection|
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