Tephra fallout in the eruption of Soufrière Hills Volcano, Montserrat

Abstract

Four mechanisms caused tephra fallout at Soufrière Hills Volcano, Montserrat, during the 1995-1999 period: explosive activity (mainly of Vulcanian type), dome collapses, ash-venting and phreatic explosions. The first two mechanisms contributed most of the tephra-fallout deposits (minimum total dense-rock equivalent volume of 23 x 106 m3), which vary from massive to layered and represent the amalgamation of the deposits from a large numbers of events. The volume of co-pyroclastic-flow fallout tephra is in the range 4-16° of the associated pyroclastic flow deposits. Dome-collapse fallout tephra is characterized by ash particles generated by fragmentation in the pyroclastic flows and by elutriation of fines. Vulcanian fallout tephra is coarser grained, as it is formed by magma fragmentation in the conduit and by elutriation from the fountain-collapse flows and initial surges. Vulcanian fallout tephra is typically polymodal, whereas dome-collapse fallout tephra is predominantly unimodal. Polymodality is attributed to: overlapping of fallout tephra of different types, premature fallout of fine particles, multiple tephra-fallout sources, and differences in density and grain-size distribution of different components. During both dome collapses and explosions, ash fell as aggregates of various sizes and types. Accretionary lapilli grain size is independent of their diameter and is characterized by multiple subpopulations with a main mode at 5ø. Satellite data indicate that very fine ash can stay in a volcanic cloud for several hours and show that exponential thinning rates observed in proximal areas cannot apply in distal areas.

Statistical analysis of dispersal and deposition patterns of volcanic emissions from Mt. Sakurajima, Japan

“…referred to as proximal and intermediate distances here) an increase in the accumulation period led to an increase in fidelity, with the opposite being true for distal stations. The inability of a single set of inverse power law parameters to cover the whole range between proximal and distal data is well known, both for single eruptions (Pyle, 1989;Fierstein and Nathenson, 1992), as well as accumulated ashfall from multiple eruptions (Bonadonna et al, 2002). Results here show that over long accumulation periods processes that lead to inhomogeneous distribution of ash near the volcano tend to be averaged out, while processes at a distance tend to be emphasised.…”

“…The intercept coefficient, w M , describes the theoretical ashfall load at a distance of 1 km from the vent, while the slope parameter shows how drastic the decrease is away from the volcano. Both parameters depend on the number of eruptions, eruptive conditions and atmospheric conditions (such as the wind fields and rainfall) during the accumulation period, such as the wind speed and rainfall (Bonadonna et al, 2002).…”

Real-time prediction of rain-triggered lahars: incorporating seasonality and catchment recovery

“…The andesitic dome-forming eruption of SHV began in July 1995 and has featured several phases of activity consisting of dome growth, dome collapse and Vulcanian explosions as well as pauses in magma extrusion (Bonadonna et al, 2002;Komorowski et al, 2010;Stinton et al, 2014). Pyroclastic density currents (PDCs) have deposited fine-grained, ash-and pumice-rich, and coarser-grained blocky deposits around the volcano (Cole et al, 2002;Stinton et al, 2014), supplemented by tephra deposits from short-lived Vulcanian explosions and associated fountain-collapse flows and surges (Komorowski et al, 2010).…”

“…Pyroclastic density currents (PDCs) have deposited fine-grained, ash-and pumice-rich, and coarser-grained blocky deposits around the volcano (Cole et al, 2002;Stinton et al, 2014), supplemented by tephra deposits from short-lived Vulcanian explosions and associated fountain-collapse flows and surges (Komorowski et al, 2010). Prevailing winds often distribute ash from weak plumes to the west, but larger plumes can also deposit to the north, east and south (Bonadonna et al, 2002). This intermittent eruptive activity has triggered a complex sedimentological response in drainages surrounding the volcano since 1995 (Barclay et al, 2006(Barclay et al, , 2007Alexander et al, 2010;Froude, 2015).…”

Conceptual Design for the Dispersal and Deposition Modelling of Fallout Ash from Mt. Baekdu Volcano

“…또한 화산재 는 지역주민과 가옥에도 영향을 미칠 수 있으며, 침 적된 강하화산재의 하중에 따라 지붕이 붕괴되거나 혹은 건물이 완전히 붕괴되는 피해를 일으킬 수 있다 (Spence et al, 2008). Bonadonna et al(2002)에 의하면, 강하화산재는 4 가지 원인으로 발생할 수 있다. 마그마성 폭발에 의 Table 1.…”