Seasonal Enhancement and Seismic Triggering by Impacts
C. Vita-Finzi (1999), JBIS, 52, 111-114
Permanent ice covers ~ 18 % of the Earth; permafrost underlies a further ~ 20 %. Response to shallow impacts will vary according to season from brittle fracture to flow accompanied by vaporisation. Seasonal climatic contrasts will thus be enhanced by sub-critical high latitude cratering, as particulate ejecta from icy targets will contribute in the winter months to the `impact winter’ effect associated with large events, and water vapour derived from thawed permafrost or melted sea- ice to the atmospheric greenhouse effect in the summer months. In seismically active areas, an impact may trigger imminent events by changing the static stress field or by ground shaking. Assessment of the environmental consequences of a sub- critical impact thus needs to consider its timing within the local seasonal or earthquake cycle as well as location, size and trajectory.