Showing papers by "Colin J. N. Wilson published in 1997"
TL;DR: The 0.76 Ma Bishop Tuff, from Long Valley caldera in eastern California, consists of a widespread fall deposit and voluminous partly welded ignimbrite as discussed by the authors.
Abstract: The 0.76 Ma Bishop Tuff, from Long Valley caldera in eastern California, consists of a widespread fall deposit and voluminous partly welded ignimbrite. The fall deposit (F), exposed over an easterly sector below and adjacent to the ignimbrite, is divided into nine units (F1‐F9), with no significant time breaks, except possibly between F8 and F9. Maximum clast sizes are compared with other deposits where accumulation rates are known or inferred to estimate an accumulation time for F1‐F8 as ca. 90 hrs. The ignimbrite (Ig) is divided into chronologically and/or geographically distinct packages of material. Earlier packages (Ig1) were emplaced mostly eastward, are wholly intraplinian (coeval with fall units F2‐F8), Lack phenocrystic pyroxenes, and contain few or no Glass Mountain‐derived rhyolite lithic fragments. Earlier packages (Ig2) were erupted mostly to the north and east, are at least partly intraplinian (interbedded with fall unit F9 to the east), contain pyroxenes, and have lithic fractions rich in G...
278 citations
TL;DR: An extremely proximal ejecta ring, with exposures to within 100 m of vent, was deposited during later-stage plinian fall activity during the 1912 Novarupta eruption in Alaska.
49 citations
TL;DR: In this article, the authors attributed the lack of early response to the high permeability of the tephra deposit and gentle relief in the areas of substantial accumulation to the area of substantial fall deposits.
Abstract: Sedimentary response to tephra deposition from substantial volcanic eruptions is generally immediate and dramatic. An important exception is the A.D. 1886 eruption of Mount Tarawera, New Zealand, which blanketed >200 km 2 with ≥50 cm of basaltic scoria and ash fall erupted from a fissure through the Tarawera dome complex. This fall deposit has suffered very little rilling or other surface erosion, and there was no immediate downstream redistribution of tephra by lahars or dilute floods. We attribute this lack of early response to the high permeability of the tephra deposit and gentle relief in the areas of substantial accumulation. Numerous small lakes occur among the dome complexes of Okataina caldera, and one direct result of the eruption was constriction of Lake Tarawera9s outflow, which caused the lake to rise substantially. Eighteen years after the eruption, collapse of a tephra bank that had controlled lake level triggered a breakout flood from this raised intracaldera lake, triggering a decades-long period of intense tributary erosion in the upper catchment and damaging stream-bed aggradation outside the caldera. This abrupt increase in sediment yield from an initially stable posteruptive landscape has no documented precedents, yet may be a common posteruptive sedimentary response in caldera complexes of temperate to humid regions.
41 citations