scholarly journals The remarkable volcanism of Shastina, a stratocone segment of Mount Shasta, California

Geosphere ◽  
2020 ◽  
Vol 16 (5) ◽  
pp. 1153-1178
Author(s):  
Robert L. Christiansen ◽  
Andrew T. Calvert ◽  
Duane E. Champion ◽  
Cynthia A. Gardner ◽  
Judith E. Fierstein ◽  
...  
Keyword(s):  
Debris Flows ◽  
Crustal Contamination ◽  
Liquid Composition ◽  
Pyroclastic Flows ◽  
The West ◽  
Pyroclastic Deposits ◽  
North Side ◽  
Eruptive Episode ◽  
Central Crater ◽  
Nearly Continuous

Abstract Mount Shasta, a 400 km3 volcano in northern California (United States), is the most voluminous stratocone of the Cascade arc. Most Mount Shasta lavas vented at or near the present summit; relatively smaller volumes erupted from scattered vents on the volcano’s flanks. An apron of pyroclastic and debris flows surrounds it. Shastina, a large and distinct cone on the west side of Mount Shasta, represents a brief but exceptionally vigorous period of eruptive activity. Its volume of ∼13.5 km3 would make Shastina itself one of the larger Holocene Cascade stratovolcanoes. Its andesite-dacite lavas average 63 wt% SiO2 and have little compositional or petrographic variation; they erupted almost entirely from one central vent, although a single vent below Shastina’s north side erupted a flow of the same composition. Eruptions ended with explosive enlargement and breaching of the central crater and successive emplacement of four, more-silicic dacite domes within the crater and pyroclastic flows down its flank. Black Butte, a large volcanic dome and pyroclastic complex below the west flank of Shastina, is petrographically and chemically distinct but only slightly younger than Shastina itself, part of a nearly continuous Shastina–Black Butte eruptive episode. Shastina overlies the widespread pumice of Red Banks, erupted from the Mount Shasta summit area and 14C dated at ca. 10,900 yr B.P. (calibrated). Shastina and Black Butte pyroclastic deposits have calibrated 14C ages indistinguishable from one another at ca. 10,700 cal. yr B.P. A cognate granitic-textured inclusion in a late Shastina lava flow yields a 238U-230Th date on zircons within error of those ages. Our conclusion that the entire, voluminous Shastina–Black Butte episode lasted no more than a few hundred years is confirmed by almost identical remanent magnetic directions of all of the lavas and pyroclastic deposits. Although extremely similar, the remanent magnetic directions do reveal a short path of secular variation through the eruptive sequence. We conclude that the entire Shastina–Black Butte eruptive episode lasted no more than ∼200 yr. The magmas that produced the Shastina and Black Butte eruptions were separate individual bodies at different crustal levels. Each of these eruptive sequences probably represents magma approximating a liquid composition that experienced only minimal differentiation or crustal contamination and remained separated from the main central conduit for most eruptions of Mount Shasta. The probability of another rapidly developing, brief but voluminous eruptive episode at Mount Shasta is low but should not be ignored in evaluating future possible eruptive hazards.

scholarly journals Carbonate debris flows in the Cambrian of south-west Peary Land, eastern North Greenland

1980 ◽  
Vol 99 ◽  
pp. 43-49
Author(s):  
J.R Ineson
Keyword(s):  
Debris Flows ◽  
Early Cambrian ◽  
The South ◽  
The West ◽  
Middle Ordovician ◽  
The North ◽  
Late Cambrian ◽  
North Side ◽  
South West ◽  
North Greenland

In south-western Peary Land a thick carbonate dominated sequence of Early to Late Cambrian Age conformably overlies the Early Cambrian Buen Formation, and is overlain, unconformably, by the Wandel Valley Formation of Early-Middle Ordovician age (Peel, 1979; Palmer & Peel, 1979). This sequence is subdivided into the Brønlund Fjord Group and the overlying Tavsens Iskappe Group (Peel, 1979; Ineson & Peel, this report). The Brønlund Fjord Group characteristically forms resistant bluffs along the north side of Wansel Dal from J. P. Koch Fjord in the west to Independence Fjord (fig. 20) in the east. The Tavsens Iskappe Group is confined to western areas by the south-easterly overstep of the Wandel Valley Formation.

scholarly journals Evidence of Unknown Paleo-Tsunami Events along the Alas Strait, West Sumbawa, Indonesia

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 46
Author(s):  
Bachtiar W. Mutaqin ◽  
Franck Lavigne ◽  
Patrick Wassmer ◽  
Martine Trautmann ◽  
Puncak Joyontono ◽  
...  
Keyword(s):  
Radiocarbon Dating ◽  
Pyroclastic Flows ◽  
Western Coast ◽  
Eastern Shore ◽  
Tsunami Deposits ◽  
The West ◽  
Marine Deposits ◽  
Sedimentary Records ◽  
The North ◽  
Large Earthquakes

Indonesia is exposed to earthquakes, volcanic activities, and associated tsunamis. This is particularly the case for Lombok and Sumbawa Islands in West Nusa Tenggara, where evidence of tsunamis is frequently observed in its coastal sedimentary record. If the 1815 CE Tambora eruption on Sumbawa Island generated a tsunami with well-identified traces on the surrounding islands, little is known about the consequences of the 1257 CE tremendous eruption of Samalas on the neighboring islands, and especially about the possible tsunamis generated in reason of a paucity of research on coastal sedimentary records in this area. However, on Lombok Island, the eruption of the Samalas volcano produced significant volumes of pyroclastic flows that entered the sea in the North and East of the island. These phenomena must have produced a tsunami that left their traces, especially on Sumbawa Island, whose western coastline is only 14 km away from Lombok’s eastern shore. Therefore, the main goal of this study is to investigate, find evidence, and determine the age of marine-origin sediments along the shore of the Alas Strait, Indonesia. We collected and analyzed samples of coral and seashells from marine deposits identified along the west coast of Sumbawa, i.e., in Belang Island and abandoned fishponds in Kiantar Village, in order to identify the sources and the occurrence period of these deposits events. Based on the radiocarbon dating of coral and seashell samples, we concluded that none of the identified marine deposits along the western coast of Sumbawa could be related chronologically to the 1257 CE eruption of Samalas. However, possible tsunami deposits located in Belang Island and abandoned fishponds in Kiantar Village yielded 4th century CE, 9th century CE, and 17th century CE. We also conclude that past large earthquakes triggered these tsunamis since no known volcanic eruption occurred near the Alas Strait at that time that may have triggered a tsunami.

Outflow ignimbrite sheets from Late Carboniferous calderas, Currabubula Formation, New South Wales, Australia

1983 ◽  
Vol 120 (5) ◽  
pp. 487-503 ◽  
Author(s):  
J. McPhie
Keyword(s):  
New South ◽  
Sedimentary Facies ◽  
Late Carboniferous ◽  
The West ◽  
Pyroclastic Deposits ◽  
Flow Units ◽  
South Wales ◽  
Accretionary Lapilli ◽  
North Eastern ◽  
Thickness Variations

SummaryRegionally mappable, silicic, outflow ignimbrite sheets are interbedded with fluvial volcanogenic conglomerates and sandstones of the Late Carboniferous Currabubula Formation of north-eastern N.S.W. Four of the most widespread of these ignimbrites are described and defined as members. The oldest member is comprised of many thin, originally non-welded flow units. Interbedded accretionary lapilli horizons may indicate phreatomagmatic activity at vent during the eruption in addition to local rain-flushing of co-ignimbrite ash clouds. Of the three other members, two are multiple flow-unit sheets, 160–180 m in aggregate thickness. Substantial portions of these sheets were originally welded. The remaining member is a simple welded ignimbrite characterized by abundant spherulites and lithophysae. Irregular pre-eruption topography and contemporaneous erosion were responsible for thickness variations of the ignimbrite sheets. Some palaeovalleys, now delineated by the ignimbrites, persisted in spite of repeated pyroclastic influxes. Relic pumice, shards and crystal fragments are ubiquitous components of the sedimentary facies of the Currabubula Formation, and were probably derived from originally poorly consolidated pyroclastic deposits such as airfall ash layers and non-welded ignimbrites. No surface trace of the sources of these ignimbrites exists. However, internal facies, thickness variations and volumes of the ignimbrites indicate that they periodically emanated from a multiple-caldera terrain which was continuously active during the Late Carboniferous, and located several kilometres to the west of present exposures.

The Early Expansion of the Kingdom of Mithridates VI

2020 ◽  
pp. 111-124
Author(s):  
Duane W. Roller
Keyword(s):  
Black Sea ◽  
Economic Benefits ◽  
The Black Sea ◽  
The West ◽  
West Side ◽  
The North ◽  
North Side

Mithridates VI the Great began his solidified rule by expanding his kingdom, seemingly with the goal of encircling the Black Sea. He gained possession of the ancient territory of Colchis and then strengthened his predecessors’ control of the Bosporos, on the north side of the sea. He also established a presence on the west side of the sea. The locals on the north side of the sea welcomed the king because they were constantly subject to barbarian pressures. There were also economic benefits to the Pontic kingdom in acquisition of the new territories. Mithridates also established a Pontic presence south and west of his kingdom, in Paphlagonia and Galatia. Yet such aggressive actions by the king were noticed by the Romans, even though the northern Black Sea was not in any region of their direct interest.

scholarly journals Epistemic uncertainties and natural hazard risk assessment – Part 2: Different natural hazard areas

2016 ◽  
Author(s):  
K. J. Beven ◽  
S. Almeida ◽  
W. P. Aspinall ◽  
P. D. Bates ◽  
S. Blazkova ◽  
...  
Keyword(s):  
Debris Flows ◽  
Volcanic Ash ◽  
Natural Hazard ◽  
Epistemic Uncertainty ◽  
Probability Distributions ◽  
Good Practice ◽  
Pyroclastic Flows ◽  
Dam Safety ◽  
Landslides And Debris Flows ◽  
Hazard Risk Assessment

Abstract. This paper discusses how epistemic uncertainties are considered in a number of different natural hazard areas including floods, landslides and debris flows, dam safety, droughts, earthquakes, tsunamis, volcanic ash clouds and pyroclastic flows, and wind storms. In each case it is common practice to treat most uncertainties in the form of aleatory probability distributions but this may lead to an underestimation of the resulting uncertainties in assessing the hazard, consequences and risk. It is suggested that such analyses might be usefully extended by looking at different scenarios of assumptions about sources of epistemic uncertainty, with a view to reducing the element of surprise in future hazard occurrences. Since every analysis is necessarily conditional on the assumptions made about the nature of sources of epistemic uncertainty it is also important to follow the guidelines for good practice suggested in the companion Part 1 by setting out those assumptions in a condition tree.

IV.—Stratigraphical Note

1907 ◽  
Vol 4 (12) ◽  
pp. 537-538
Author(s):  
T. C. Cantrill
Keyword(s):  
Geological Survey ◽  
The West ◽  
The Road ◽  
The North ◽  
North Side ◽  
The Town

The fossils which Mr. V. M. Turnbull has collected from supposed Slade Beds on the “roadside near St. Martin's Cemetery, Haverfordwest,” were obtained along the north side of a road leading westward from St. Martin'ls Cemetery to Portfield House, on the west aide of the town. About half-way between the Cemetery and Port-field House the road is crossed by a by-road known as Jury Lane; one of the fossiliferous localities lies 110 yards east of Jury Lane crossing, another is 100 to 150 yards west of it. The area in question is contained in the Old Series one-inch Geological Survey map, Sheet 40, the New Series one-inch map, Sheet 228, and in the six-inch map, Pembrokeshire, Sheet 27 N.E.

Characterizing the last explosive gasps of the Piton des Neiges (La Réunion Island) over the last 200 ka

2020 ◽  
Author(s):  
Maria Paula Castellanos Melendez ◽  
Ben Ellis ◽  
Oscar Laurent ◽  
Jan Wijbrans ◽  
Klaudia Kuiper ◽  
...  
Keyword(s):  
Single Crystal ◽  
Current View ◽  
Density Currents ◽  
Large Area ◽  
Pyroclastic Deposits ◽  
The Past ◽  
Wide Range ◽  
Eruptive Episode ◽  
Alkali Feldspars

<p>The most recent activity of Piton des Neiges (La Réunion) is characterized by explosive behavior and relatively evolved magma compositions. These eruptions occurred roughly over the past 200 thousand years producing thick pyroclastic deposits, lava domes and block and ash flow deposits. We here present a detailed petrologic and geochronologic characterization of these deposits providing insights into the timing of explosive eruptions and pre-eruption magma storage conditions.</p><p>The early phase of explosive activity is characterized by up to 15 m-thick pyroclastic deposits found on the southeastern and western flanks of Piton des Neiges. These deposits have been regarded as individual discrete eruptions that occurred between 220 and 110 ka. Our detailed petrographical and geochemical study on juvenile fragments and the main mineral phases indicate that all deposits share similar geochemical fingerprints. High-precision single crystal <sup>40</sup>Ar/<sup>39</sup>Ar dates on 70 alkali feldspars from 6 samples reveal significant dispersion but the youngest population of dated crystals from each sample yield overlapping weighted mean dates around 200 ka, supporting their geochemical correlation. The wide spread in <sup>40</sup>Ar/<sup>39</sup>Ar dates of up to 88 kyrs prior to eruption, uncommon for alkali feldspar in volcanic rocks, argues for the presence of excess and/or inherited argon in those crystals. Together, our findings suggest that the early pyroclastic deposits are the product of a Plinian-type eruption that covered a large area of the island around 200 ka. The eruption was fed by a long-lived magma reservoir that produced differentiated magmas in response to lower recharge fluxes after the main active center migrated to the currently active Piton de la Fournaise. A wide range of mineral compositions and the strong disequilibrium between crystals and the trachytic groundmass is an indication of the pronounced heterogeneity of the magmatic reservoir following a deep recharge event that triggered the eruption.</p><p>The younger eruptive episode of Piton des Neiges occurred between 70 and 30 ka with dome-forming lavas of trachytic to rhyolitic composition that collapsed into pyroclastic density currents resulting in block and ash flow deposits found closer to the current summit. This eruptive style, infrequent in this geotectonic setting, has not yet been well recognized for Piton des Neiges. Pristine zircon crystals, found in a sample from a block and ash deposit, were dated with a total of 192 LA-ICP-MS spot analyses using the U-Th disequilibrium method, and constitute the first zircon geochronology study for this volcano. The results yield a well-defined isochron with a date of 44.80 ± 1.32 ka (2 S.E., MSWD = 1.2). Single crystal <sup>40</sup>Ar/<sup>39</sup>Ar dates on alkali feldspars show a similar dispersion as for the older eruptive phase, but the youngest dates overlap with the zircon U-Th date, providing robust estimates of the eruption age.</p><p>This detailed characterization of the youngest eruptive episode of Piton des Neiges documents its explosive potential during the past 200 thousand years and has significant implications regarding the current view of Piton des Neiges as an extinct volcano.</p>

Sediment Induced Disasters in the World and 1999-Debris Flow Disasters in Venezuela

2010 ◽  
Vol 5 (3) ◽  
pp. 229-235 ◽  
Author(s):  
Takahisa Mizuyama ◽  
◽  
Shinji Egashira ◽  
Keyword(s):  
Debris Flows ◽  
Pyroclastic Flows ◽  
Hazard Maps ◽  
Strong Earthquakes ◽  
Control Structures ◽  
The World ◽  
Hazard Education ◽  
And Control ◽  
Landslides And Debris Flows ◽  
Sediment Disaster

Many sediment related disasters have occurred in many areas of the world. The table of sediment related disasters from 1997 to 2006 is shown. It shows strong earthquakes and super hurricanes/typhoons cause large landslides and debris flows. Climate change may trigger larger disasters more frequently in the future. Stratovolcanoes are geologically weak and cause huge landslides and debris avalanches. Active volcanoes release lava flows and pyroclastic flows, which cause serious damages. As an example of a typical sediment disaster, a disaster which occurred in Venezuela, in 1999 is briefly reported. The disaster was caused by unusual heavy rainfall. Many people were killed by many debris flows and shallow landslides. The disaster shows information on hazards such as hazard maps and rainfall is necessary and control structures may reduce damages if they had existed. Proper land-use and hazard education are needed.

Galaesus

1947 ◽  
Vol 41 (3-4) ◽  
pp. 93-94
Author(s):  
T. J. Dunbabin
Keyword(s):  
George Gissing ◽  
Ionian Sea ◽  
The West ◽  
West Side ◽  
Small Stream ◽  
The North ◽  
North Side

In his masterly work on Tarentum, P. Wuilleumier (Tarente, 5) identifies the Galaesus with the Citrezze or Giadrezze, a small stream running into the north side of the Mare Piccolo, about two miles from the channel on the west side of the citadel of Tarentum which connects the Mare Piccolo with the sea. This identification, which has been often repeated since Lenormant's time (La Grande-Grèce, i. 19) and spread beyond the narrow bounds of pure scholarship by the writings of George Gissing (By the Ionian Sea, 60 ff.), Norman Douglas (Old Calabria, 80), and David Randall-Madver (Greek Cities in Italy and Sicily, 76), is likely to hold the field by virtue, of Wuilleumier's support. But it is irreconcilable with the only ancient evidence on the position of this river, given in the account of Hannibal's movements in 212 B.C.

Note on the Occurrence of Dayia navicula (J. de C. Sowerby) in the Lower Ludlow Rocks of Shropshire

1939 ◽  
Vol 76 (8) ◽  
pp. 360-361 ◽  
Author(s):  
J. Shirley
Keyword(s):  
Thin Layer ◽  
The West ◽  
West Side ◽  
Great Thickness ◽  
Railway Line ◽  
North East ◽  
The North ◽  
North Side ◽  
Large Numbers ◽  
Type Area

In the type area the Ludlow Rocks generally have been divided into Lower Ludlow Shales, Aymestry Limestone, Dayia Shales and Whitcliffe Flags in upward sequence. The Dayia Shales are characterized by the presence of enormous numbers of Dayia navicula (J. de C. Sowerby). This preponderance of D. navicula in the shales immediately above the Aymestry Limestone has caused a tendency to regard beds in other localities containing this fossil as being on the same stratigraphical horizon in spite of the character of the accompanying fauna. In two recent papers on the Ludlow Rocks of the Welsh Borderland (Straw, 1937, and Earp, 1938) it has been shown that D. navicula ranges through at least 3,000 feet of strata, occurring commonly throughout this great thickness and outlasting more than one change of fauna. Although, in this area, the brachiopod ranges from the zone of Monograptus nilssoni into the Upper Ludlow it has not hitherto been recorded below the Aymestry Limestone in Shropshire. This gap in our knowledge is now filled by the discovery of specimens in Lower Ludlow Shales exposed in a small quarry 40 yards north-east of Stokewood Cottage, which is on the west side of the railway line a little over a mile south of Craven Arms. The quarry shows about 15 feet of nodular shales with thin limestone seams. The commonest fossils are Chonetes laevigata (J. de C. Sowerby), C. minima (J. de C. Sowerby), and Stropheodonta filosa (J. de C. Sowerby) which occur in large numbers on some of the bedding surfaces. Other fossils are Stropheodonta euglypha (Dalman), Delthyris sp., Orthoceras sp., Dalmanites sp., and a plectambonitid. Dayia navicula seems to be confined to a thin layer on the north side of the quarry. Graptolites referable to Monograptus cf. chimaera occur fairly commonly. About 400 yards in a south-easterly direction another small quarry exposes Conchidium Limestone which is about 170 feet stratigraphically above the beds in the first quarry.

Sign in / Sign up

Export Citation Format

Share Document