PRELIMINARY-STUDY OF ELECTROMAGNETIC EMISSIONS FROM CRACKS IN ICE

In a first attempt to understand the nature of observed electromagnetic emissions from large ice sheets and glaciers during fracture, it was hypothesized that internal microcracking played a role in causing this phenomenon. Laboratory-based experiments were conducted in search of evidence to support this view. It was determined that signals could be correlated with individual cracks within the bulk of a test sample. Three types of signal were observed: exponentially decaying signals with amplitudes under 10 mV and durations between 0.15 and 1.0 ms were produced by grain-boundary type cracks (i.e. small stable through-thickness or partial-through-thickness cracks of the order of grain diameter in length); axial splits (i.e. larger planar cracks usually running the length of the sample) caused similarly shaped signals with larger amplitudes (tens to hundreds of millivolts) and longer durations (1-10 ms); the third signal type exhibited a sinusoidally decaying form and is attributed to the complex interaction of multiple cracks within the ice. While experimental evidence strongly suggests a correlation between cracking and signal emission, more work must be done to characterize the effects of crack orientation. location and size on the polarity and magnitude of observed signals.