to the tip). This discrepancy could arise from small os-
formation either on the distance from the receiver to the
avalanches nor on the types of antenna used. While all
cillations of the crack surfaces if there is a constant
the mechanisms of EME from ice considered above are
potential difference between them.
Similar EME from cracks were observed by Thiel
applicable for numerous cracks in a snow cover during
(1992). He recorded EME in the vicinity of ice cracks
an avalanche, there may be some additional phenome-
created by breaking rods of ice, scouring the ice sur-
na, such as frictional electrification, responsible for the
face, applying uniaxial pressure to a cylindrical ice
EME from snow avalanches.
core and using a bore-hole jack in an ice sheet. The
The same authors reported detection of magnetic sig-
observations were made in the frequency band from
nals captured from a mountain glacier (Malyy Azau gla-
50 Hz to 15 kHz, using a two-channel audio cassette
cier in the Caucasus Mountains) during various natural
recorder and wire probes inside or outside the ice.
and artificially induced dynamic processes. The EME
and seismic signals were recorded in the 0.1- to 30-Hz
emissions events that arise during crack formation.
frequency range. The magnetic component was cap-
tured with a single-turn loop with a diameter of 100 m
Field experiments
and with an induction coil with a Permalloy core. Figure
At present we have several reports on observations
27, taken from the paper by Kachurin et al. (1979),
of EME from lake ice, glaciers and sea ice sheets. Ka-
shows the correlation between EME and seismic signals
churin et al. (1979) reported the detection of electrical
captured from the glacier. Later, Kachurin et al. (1984)
and magnetic signals from ice and snow under field
reported EME from freshwater lake ice and sea ice
conditions. Radio waves emitted by the motion of
sheets. To measure the horizontal component of the
snow avalanches were recorded by a set of radio-fre-
magnetic field, they used an induction coil with a reso-
quency receivers working in the frequency ranges of
0.1 to 30 Hz, 900 Hz to 2 kHz, 2.5 MHz, 40 MHz and
detected during air cooling at night and during ice hum-
760 MHz. The electrical component of EME was re-
mocking. In the same study Kachurin and his co-authors
corded at 760 MHz, and the magnetic component at
measured quasi-static (102 to 1 Hz) electrical fields
the other frequencies. The sensitivity of the detectors
generated in first-year sea ice during its loading. When
over all frequencies was 1 to 2 V/m. Broadband EME
the load was applied they detected an electrical potential
with a maximum near 1 kHz were recorded for ava-
difference of a few millivolts between two electrodes
lanches of freshly fallen snow and near 2.5 MHz for
mounted into the ice at a distance of 50 m from each
packed snow. The amplitudes of the electromagnetic
other. The corresponding bend of the ice sheet was
signals investigated were one to two orders of magni-
about 104 radian.
tude higher than that of background noise in the same
They also made a very interesting attempt to detect
corresponding range. The authors did not provide in-
sea ice EME from an airplane flying at an altitude of 100
30
20
10
0
*
*
*
*
5
0
-5
0
20
40
60
20
40
60
80
100
120
140
0
Figure 27. Synchronous records of the electromagnetic (top) and seis-
mic (bottom) signals captured from natural and artificially induced gla-
cier tremors on 17 August 1977 (after Kachurin et al. 1979). The pass
band of the electromagnetic and seismic signals is 0.1 to 30 Hz.
20
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