Age Determination of the Kawagodaira Volcanic Eruption in Japan by 14C Wiggle-Matching

The Kawagodaira Volcano is located on the northwest slope of Amagi Volcano on the Izu Peninsula of central Japan. The fine pumice that erupted from Kawagodaira Volcano is widely distributed in the central and western parts of the Japanese mainland. Here, we report an accurate eruption age determined by radiocarbon wiggle-matching of a Japanese cedar timber excavated from the pyroclastic deposit at the pumice flow terminal of Kawagodaira Volcano. The 14C wiggle-match estimate for the Kawagodaira Volcano eruption is 1210–1187 cal BC (95.4% confidence level).

Emmons Lake Volcanic Center, Alaska Peninsula: source of the Late Wisconsin Dawson tephra, Yukon Territory, Canada

The Emmons Lake Volcanic Center on the Alaska Peninsula of southwestern Alaska is the site of at least two rhyolitic caldera-forming eruptions (C1 and C2) of late Quaternary age that are possibly the largest of the numerous caldera-forming eruptions known in the Aleutian arc. The deposits produced by these eruptions are widespread (eruptive volumes of >50 km3 each), and their association with Quaternary glacial and eolian deposits on the Alaska Peninsula and elsewhere in Alaska and northwestern Canada enhances the likelihood of establishing geochronological control on Quaternary stratigraphic records in this region. The pyroclastic deposits associated with the second caldera-forming eruption (C2) consist of loose, granular, airfall and pumice-flow deposits that extend for tens of kilometres beyond Emmons Lake caldera, reaching both the Bering Sea and Pacific Ocean coastlines north and south of the caldera. Geochronological and compositional data on C2 deposits indicate a correlation with the Dawson tephra, a 24 000 14C BP (27 000 calibrated years BP), widespread bed of silicic ash found in loess deposits in west-central Yukon Territory, Canada. The correlation clearly establishes the Dawson tephra as the time-stratigraphic marker of the last glacial maximum.

Late quaternary explosive silicic volcanism on St Lucia, West Indies

Many explosive eruptions of dacitic magmas have occurred on St Lucia during the late Quaternary. These have produced widespread aprons and fans of pumice flow and ash flow deposits radiating around the central highlands, with co-eruptive air-fall and surge layers interbedded with palaeosols and epiclastic deposits. Vents in the highlands have not been located because of the dense tropical jungle but we suspect they are now plugged by lava domes surrounded by aprons of block and ash flow deposits. Young magmatically related dacitic lava domes have been extruded in the Qualibou depression. The pumice succession can be divided into older quartz-poor deposits forming the Choiseul Pumice and younger crystal-rich deposits with abundant large quartz which are called the Belfond Pumice. The Choiseul Pumice groups together scattered remnants of the products of many eruptions of different low-silica dacitic magma types. The Belfond Pumice is the product of several eruptions of a high-silica magma type and 14C ages have dated these between 20900 to 34200 years B.P.The pumice flow deposits occur as small-volume valley fills. A granulometric study of Belfond pumice flow deposits shows them to be strongly depleted in finer ash and vitric components. It is suggested that the narrow, winding and vegetated valleys on the island locally induced turbulence and the flows moved with large, highly fluidized and inflated heads, resulting in substantial loss of fine vitric ash. One ash flow deposit which is extremely rich in crystals and carbonized vegetation is highly depleted in fines and shows enhanced vitric losses. This flow may have been a much more violent ash hurricane or blast which surmounted topography ingesting large amounts of lush vegetation. Ignition of this released the large quantities of gas needed to elutriate most of the fines.A model is suggested for the recent volcanic activity on St Lucia in which separate batches of silicic magma, each having a distinctive petrological and chemical character, rose into high level chambers over a large area. Eruptions of volatile-rich magma led to highly explosive pumice-forming activity from vents in the central highlands. Degassed and more crystal-rich magma was extruded later from the same vents or in the attenuated flank of the Qualibou depression to from lava dome complexes.