A model for the 1975–1976 Tolbachik eruption, Kamchatka, as deduced from geodetic data

Tectonophysics,

153

91 (1983) 153

Elsevier Science Publishers

B.V., Amsterdam

2. Crustal Deformations

- Printed

associated with Volcanism

A MODEL FOR THE 19751976 DEDUCED

in The Netherlands

FROM GEODETIC

TOLBACHIK

ERUPTION, KAMCHATKA,

AS

DATA

V.B. ENMAN Institute

of Physics of the Earth, Academy of Sciences of the U.S.S.R.,

(Received

March

Moscow (U.S.S.R.)

10, 1983)

ABSTRACT

Geodetic Tolbachik

measurements

made between

fissure eruption

of crustal deformations:

of 1975-1976

1971 and 1978 in the region of the large in Kamchatka

(1) uplift and extension

eruption;

and (2) subsidence

volcanoes

occurring

and compression

after the eruption.

revealed

two general

of a large area occurring

types

during

the

of the zone near the newly-formed

Furthermore,

rapid

horizontal

and vertical

displacements of the area adjacent to the eruption region occurred during the eruption. Displacements both preceding and occurring after the magma issue to the surface have been measured. Their duration was found to be from a few minutes to several days. Crustal deformations associated with volcanic activity may be caused by pressure sources located at certain depths below volcanoes. The configuration and the origin of pressure column

sources may be different

or dyke), but the deformation

Based on these simulations, source

were calculated.

earth’s

surface

calculated

(feeding channel,

source mechanism

the depth

and radius

This source creates

best coinciding

peripheral

with geodetic

chamber,

intruding

in all cases is the same.

of a simple spherical

pressure

a field of elastic displacements data.

The magma

from data on the width and length of a fissure during

the surface. It proved to be not more than 300 kg/cm*. sources was deduced from data on vertical displacements.

overpressure

of the was

the magma issue to

the location of pressure Based on these data, the

existence and depths of two shallow magma chambers which fed the North vents eruption have been calculated. They are located at depths of about 6 and 1.5 km, one over another. Verification of the calculated deformation sources was supported by deep seismic sounding data. TWO seismic shadows apparently caused by the melt occurrence in the magma chambers have been detected at just these same depths.

0040-1951/83/$03.00

0 1983 Elsevier Science Publishers

B.V.