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

2003 ◽  
Vol 40 (7) ◽  
pp. 925-936 ◽  
Author(s):  
Margaret T Mangan ◽  
Christopher F Waythomas ◽  
Thomas P Miller ◽  
Frank A Trusdell
Keyword(s):  
Compositional Data ◽  
Late Quaternary ◽  
Yukon Territory ◽  
Volcanic Center ◽  
Pyroclastic Deposits ◽  
Alaska Peninsula ◽  
Aleutian Arc ◽  
Pumice Flow ◽  
North And South ◽  
The Bering Sea

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.

Identification of Dacitic Tephra by Activation Analysis of their Primary Mineral Phenocrysts

1973 ◽  
Vol 3 (2) ◽  
pp. 307-315 ◽  
Author(s):  
M.J. Dudas ◽  
M.E. Harward ◽  
R.A. Schmitt
Keyword(s):  
Rare Earth ◽  
Activation Analysis ◽  
Pacific Northwest ◽  
Late Quaternary ◽  
Minor Element ◽  
Transition Elements ◽  
Pyroclastic Deposits ◽  
Element Abundances ◽  
The Pacific ◽  
Primary Mineral

AbstractPrimary mineral phenocrysts from eight different late Quaternary pyroclastic deposits were fractionated for neutron-activation analysis with the purpose of characterizing each of the deposits on the basis of trace and minor element compositions. In hornblende separates, contents of several rare earth and transition elements were found to be distinctive for the Mazama, Glacier Peak, and several St. Helens deposits. In magnetites, abundances of transition elements are characteristic and serve as good discriminants for the pyroclastic deposits examined in this investigation. Contents of transition and rare earth elements in hyperthenes also appear useful in distinguishing volcanic ash deposits. Trace and minor element abundances in plagioclase phenocrysts did not appear adequate for identification of pyroclastics due to elemental depletion and similarity of contents for feldspar separates. It was found that contents of Sm and Yb in hornblende phenocrysts would serve to distinguish between several pyroclastic deposits from the Pacific Northwest.

Arctic archaeologies: recent work on Beringia

Antiquity ◽  
2015 ◽  
Vol 89 (345) ◽  
pp. 740-742 ◽  
Author(s):  
Herbert Maschner
Keyword(s):  
Bering Sea ◽  
North Pacific ◽  
Yukon Territory ◽  
The Arctic ◽  
Land Bridge ◽  
Far North ◽  
North East ◽  
Bering Land Bridge ◽  
Last Glaciation ◽  
The Bering Sea

This review considers three books on the archaeology of territories situated around the Bering Sea—a region often referred to as Beringia, adopting the term created for the Late Pleistocene landscape that extended from north-east Asia, across the Bering Land Bridge, to approximately the Yukon Territory of Canada. This region is critical to the archaeology of the Arctic for two fundamental reasons. First, it is the gateway to the Americas, and was certainly the route by which the territory was colonised at the end of the last glaciation. Second, it is the place where the entire Aleut-Eskimo (Unangan, Yupik, Alutiiq, Inupiat and Inuit) phenomenon began, and every coastal culture from the far north Pacific, to Chukotka, to north Alaska, and to arctic Canada and Greenland, has its foundation in the cultural developments that occurred around the Bering Sea.

Seismic imaging evidence that forearc underplating built the accretionary rock record of coastal North and South America

2019 ◽  
Vol 158 (1) ◽  
pp. 104-117 ◽  
Author(s):  
David W. Scholl
Keyword(s):  
South America ◽  
Subduction Zones ◽  
Seismic Imaging ◽  
Southern Chile ◽  
Late Palaeozoic ◽  
Aleutian Arc ◽  
Seaward Edge ◽  
Metamorphic Facies ◽  
North And South America ◽  
North And South

AbstractThe submerged forearcs of Pacific subduction zones of North and South America are underlain by a coastally exposed basement of late Palaeozoic to early Tertiary age. Basement is either an igneous massif of an accreted intra-oceanic arc or oceanic plateau (e.g. Cascadia(?), Colombia), an in situ formed arc massif (e.g. Aleutian Arc) or an exhumed accretionary complex of low and high P/T metamorphic facies of late Palaeozoic (e.g. southern Chile, Patagonia) and Mesozoic age (e.g. Alaska). Seismic studies at Pacific forearcs image frontal prisms of trench sediment accreted to the seaward edge of forearc basement. Frontal prisms tend to be narrow (10–40 km), weakly consolidated and volumetrically small (∼35–40 km3/km of trench). In contrast, deep seismic imaging of submerged forearcs commonly reveals large volumes (∼2000 km3/km of trench) of underplated material accreted at subsurface depths of ∼10–30 km to the base of forearc basement. Underplates have been imaged below the southern Chile, Ecuador–Colombia, north Cascade, Alaska, and possibly the eastern Aleutian forearcs. Deep underplates have also been observed below the Japan and New Zealand forearcs. Seismic imaging of northern and eastern Pacific forearcs supports the conclusion drawn from field and laboratory studies that exposed low and high P/T accretionary complexes accumulated in the subsurface at depths of 10–30 km. It seems significant that imaged underplated bodies are characteristic of modern well-sedimented subduction zones. It also seems likely that large Pacific-rim underplates store a significant fraction of sediment subducted in Cenozoic time.

Late Quaternary caldera-forming eruptions in the eastern Aleutian arc, Alaska

Geology ◽  
1987 ◽  
Vol 15 (5) ◽  
pp. 434 ◽  
Author(s):  
Thomas P. Miller ◽  
Robert L. Smith
Keyword(s):  
Late Quaternary ◽  
Aleutian Arc

Late quaternary explosive silicic volcanism on St Lucia, West Indies

1984 ◽  
Vol 121 (1) ◽  
pp. 1-15 ◽  
Author(s):  
J. V. Wright ◽  
M. J. Roobol ◽  
A. L. Smith ◽  
R. S. J. Sparks ◽  
S. A. Brazier ◽  
...  
Keyword(s):  
Late Quaternary ◽  
Large Area ◽  
Lava Domes ◽  
Flow Deposit ◽  
Pumice Flow ◽  
Valley Fills ◽  
High Silica ◽  
Chemical Character ◽  
Central Highlands ◽  
High Level

AbstractMany 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.

scholarly journals ВИХРЕВАЯ СТРУКТУРА ВОСТОЧНО-КАМЧАТСКОГО ТЕЧЕНИЯ ПО СПУТНИКОВЫМ НАБЛЮДЕНИЯМ

2019 ◽  
Author(s):  
N.M. Vakulskaya ◽  
V.A. Dubina ◽  
V.V. Plotnikov
Keyword(s):  
Bering Sea ◽  
Life Time ◽  
Winter Monsoon ◽  
Synoptic Scale ◽  
The North ◽  
Kamchatka Current ◽  
North And South ◽  
Multisensor Data ◽  
Mesoscale Cyclones ◽  
The Bering Sea

На основе анализа архива спутниковых мультисенсорных данных исследована динамика ледяного покрова в области ВосточноКамчатского течения. При развитом зимнем муссоне плавучий лёд смещается вдоль побережья Камчатки на юг, трассируя разномасштабные вихри, которые возникают при взаимодействии потока ВосточноКамчатского течения с неоднородностями береговой черты и континентального склона. Средняя скорость дрейфа, рассчитанная по изображениям, полученным в марте 2016 г. в один день с разницей в 110 мин, составила 0,25 м/с, что в два с половиной раза превысило суточное значение. На севере и на юге района значения скорости дрейфа превышали скорости в центральной части. При ослаблении зимнего муссона в поле дрейфующего льда в западной части Берингова моря образуются хорошо выраженные грибовидные структуры, горизонтальные размеры которых могут превышать 200 км. Наряду с известными ранее синоптическими вихревыми образованиями синоптического масштаба спутниковые данные высокого (10 15 м) и среднего (250 м) пространственного разрешения позволили зарегистрировать многочисленные мезомасштабные циклоны диаметром 10 25 км и временем жизни от 1 до 14 суток.On the basis of the analysis of the satellite multisensor data archive, the dynamics of the ice cover in the region of the East Kamchatka Current is investigated. With the developed winter monsoon, floating ice shifts along the Kamchatka coast to the south, tracing the multiscale eddies that appear when the East Kamchatka stream interacts with the inhomogeneities of the coastline and the continental slope. The average drift speed calculated from images taken in March 2016 on the same day with a difference of 110 min was 0.25 m / s, which was two and a half times higher than the daily value. On the north and south of the region, the drift velocity values exceeded the velocities in the central part. With the attenuation of the winter monsoon in the field of drifting ice in the western part of the Bering Sea, welldefined mushroomlike structures are formed, the horizontal dimensions of which can exceed 200 km. Together previously known synoptic eddy formations of a synoptic scale, satellite data of high (10 15 m) and moderate (250 m) spatial resolution made it possible to register numerous mesoscale cyclones with a diameter of 10 25 km and a life time of 1 to 14 days.

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