Eruptive Process, Effects and Deposits of the 1996 and the Ancient Basaltic Phreatomagmatic Eruptions in Karymskoye Lake, Kamchatka, Russia

Abstract

On 2-3 January 1996 an explosive eruption discharging = l0 6 kgs -1 of basaltic magma occurred in Karymskoye lake at an initial water depth of ~ 50 m. Characteristics of the deposits together with analyses of a videotape of several explosions have allowed us to model the eruptive events. Initial vent-clearing phreatic explosions ejected blocks of country rocks (up to 3 m diameter) to distances of up to 1.3 km. Then followed 10-20 h of phreatomagmatic Surtseyan activity (100-200 outbursts of water-gas-pyroclastic mixtures to heights of up to 1 km, with initial velocities of 110 m s -1 |. The eruption slugs collapsed back into the lake and produced base surges (runout up to 1.3 km; average velocity 12.5 m s -1 ). The convective eruption plume rose to a height of 3 km and deposited a thin distal fall deposit. The eruption ended with the ejection of scoria-crust bombs (specific basaltic bombs with dense core and scoriaceous crust).Pyroclasts of the eruption are mostly poorly to moderately vesicular juvenile basaltic particles shaped by a combination of magmatic vesiculation and magma-water interaction. Ninety-five percent of the products (0.047 km 3 ) formed an underwater tuff ring composed of parallel layers of moderately to poorly sorted lapilli ash and ash lapilli (Md -3.9 to 0.6 phi; sorting 1.5-3.2 phi), each 10-60 cm thick. They were deposited by water-rich base surges that originated from Surtseyan type eruption bursts. The most widespread hazards of the eruption were tsunamis and lahars. At distances < 1.3 km from the crater, base surges and ballistic clasts were very destructive.Eruptive activity in the lake before 1996 included two eruptions at c. 4800 14 C yr BP. The first left deposits similar to those of the 1996 eruption and thus is interpreted as a Surtseyan eruption that occurred at the same water depth as in 1996. The second of the 4800 l4 C yr BP eruptions deposited extensive cross-laminated base-surge deposits and is interpreted to have occurred in very shallow water.

Deposits, character and timing of recent eruptions and gravitational collapses in Tatun Volcanic Group, Northern Taiwan: Hazard-related issues

“…Very poor sorting, coarse grain size, blocky morphology of particles and low vesicularity of juvenile clasts in these deposits are similar to explosive breccias of wet phreatomagmatic eruptions (Wohletz and Sheridan, 1983;Belousov and Belousova, 2001).…”

A combined field and numerical approach to understanding dilute pyroclastic density current dynamics and hazard potential: Auckland Volcanic Field, New Zealand

“…A definitive version was subsequently published in Journal of Volcanology and Geothermal Research, (2014 (Moore 1967). The model also reasonably predicts the deposit distribution for the 1965 eruption of Taal and the 1996 eruption at Karymskoye Lake, using well-constrained grain-size characteristics and observations (Moore 1967;Belousov and Belousova 2001) and assuming that sedimentation rate is a reasonable proxy for deposit distribution.…”

“…We also assume dilute, incompressible flow at atmospheric pressure, and radial propagation away from source. Radial propagation in the case of base surges is a result of the collapse of discrete "cock's tail jets", "eruption slugs" and/or eruption columns as noted by several sets of observations, including those in Mastin and Witter (2000), Belousov andBelousova (2001), andNemeth et al (2006).…”

“…Note that the velocity does not go to zero; rather the current stops moving laterally when the bulk density is equivalent to the atmospheric density. We can interpret this location to be the point of lift-off, where ground-parallel velocity transitions to vertical velocity by means of a buoyant plume, as is common in PDCs and base surges (i.e., Woods and Bursik, 1994;Belousov and Belousova, 2001). With these conditions, P dyn up to 80 kPa can be expected closer to the vent (within 0.5 km).…”

Generation of pyroclastic flows by explosive interaction of lava flows with ice/water-saturated substrate

“…Wohletz, 1983;Heiken and Wohletz, 1985;Büttner et al, 1999;Morrissey et al, 2000;White and Houghton, 2000;Belousov and Belousova, 2001;Büttner et al, 2002). Voluminous lahars, simultaneously outpoured from the locations of explosions, indicate that water was available in large amount in the moment of the PF generation.…”