Abstract

Particulate separation and analysis of the fine fractions in nine dated deep-sea sedimentary cores, extending from high latitudes of the southwest to south-central Pacific, reveal very similar time patterns in the accumulation of atmospherically transported rhyolitic volcanic dust during the past 2.5 m.y. The probable source region for the volcanic dust is the Balleny Islands. Simple comparisons of the accumulation-rate curves show that the same series of volcanic eruptions are undoubtedly recorded in the cores examined for the period of 2.4 to 0.3 m.y. ago. Seven separate periods of intensive volcanic activity, each containing as many as eight possibly distinct eruptive episodes, have been detected. The most intense eruptions occurred between 1.8 and 1.6 m.y. ago. The associated volcanic ash will be found in high-latitude marine sediments of the entire South Pacific. We name this widespread deposit the “Eltanin Ash.” The average volcanic-dust production rate for the 88- to 11-µm size fraction was of the order of 1.7 × 105tons/yr over an area of 4 × 106 km2, for a period of up to 2 × 105 yr.

Beyond 500 km from the source, the glass accumulation rates decrease exponentially with increasing distance in most cases. Deviations from this generalization are suspected to be caused by processes including differential dispersal by oceanic currents, bioturbation, bottom or turbidity currents, and minor fluctuations of sedimentation rates, but we can demonstrate minimal distortion for selected eruptions.

We have estimated the paleoexplosivity of the series of major eruptions using methods described in an earlier paper. An energy equivalent to 40 megatons of TNT is suggested for the maximum explosivity of the eruptions. This is about 40 times the energy of the suggested violence of the 1968 Arenal Volcano eruption, but only 20 to 40 percent of the 1883 Krakatoa eruption.

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