Discussion of ‘Structure and eruptive mechanisms at Surtsey Volcano, Iceland’ by J. G. Moore
No abstract available.
Geological Magazine↗
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Structure and eruptive mechanisms at Surtsey Volcano, Iceland
Glassy basalt tuff was the primary material cored in 1979 from a 181 m deep drill hole on the east tuff ring of Surtsey volcano. Despite the fact that the hole extends 122 m below sea level all the core is similar to the exposed tephra composing the two tuff rings of the island. The tuff includes abundant accretionary lapilli and tuff vesicles, indicating that it was all deposited subaerially. During the growth of the tuff rings, repeated hydromagmatic explosion cycles began with a series of intermittent tephra-finger explosions leading up to continuous uprush explosions which lasted for several minutes to several hours. This nozzle-like continuous activity produced eruption columns 100–250 m in diameter and 500–2000 m in height which probably quarried several hundred metres below the ground surface. The continuous-uprush explosion type provides a reasonable mechanism to excavate a diatreme from the top down. During construction of the tuff rings, concentric faults repeatedly downdropped a funnel-like structure (400–800 m in diameter) several hundred metres, thus accounting for the presence of subaerially deposited tephra in the drill core far beneath sea level. Ring dykes later intruded upward along these faults and fed small lava flows. Heat in the surface tephra probably originated primarily from these shallow intrusions.
Geological Magazine↗
Significance of lineation and minor folds near major thrust faults in the southern Appalachians and the British and Norwegian Caledonides
The Blue Ridge thrust sheet is one of the principal thrust masses of metamorphic rocks in the southern Appalachians. A broad zone of sheared and retrogressively metamorphosed rocks near the sole of the thrust sheet around the Grandfather Mountain window displays numerous small tight or isoclinal folds having axes subparallel to an intense penetrative cataclastic a lineation and axial planes parallel to foliation in the thrust sheet. These folds seem to have formed by tightening, flattening, and passive rotation of earlier more open folds originally formed perpendicular to the direction of transport. The style and orientation of these folds closely resemble those of analogous structures in thrust masses of crystalline rocks in the Caledonian orogenic belt in Scotland and Norway, suggesting that the structures of both regions may have similar origins.
Alabama, Georgia, Kentucky, Maryland, North Caroli↗
II.-Note on Some Appendages of the Trilobites
The results of Mr. W. S. Valiant's long search for the appendages of Trilobites have recently been made known by Mr. W. B. Matthew, who described the material sold to the Columbia College of New York by Mr. Valiant. Mr. Valiant informs me that he discovered traces of what he considered to be antennæ, and that for several years he continued collecting until he found a locality where the specimens were well preserved and showed, not only the antennæ, but legs and what he supposed to be the swimming appendages.
Geological Magazine↗
I.-Subaerial Deposits of the Arid Region of North America
The subaërial deposits now accumulating in the arid portion of the United States may be divided into four classes: 1, Eolian Sands; 2, Talus Slopes; 3, Alluvial Cones; and 4, Calcareous Clays to which no specific name has been applied, but which, for reasons stated below, will be called “adobe” in this paper.
Geological Magazine↗
II.-Subaerial Deposits of the Arid Region of North America
A Comparison of adobe with the loess of China forms the concluding part of this paper; but as no analyses of the Chinese deposit are known to me, a few analyses of the loess of the Mississippi Valley are inserted, not with the assumption, however, that the deposits bearing the same name in these two regions are identical. A comparison of this table with the one showing the composition of adobe is instructive, as it indicates that these two yellow earths have a very similar composition. There are other respects in which they bear a close resemblance to each other; but as my acquaintance with the loess of the Mississippi Valley is limited, this comparison will not be carried further.
Geological Magazine↗
I.-The Jordan-Arabah Depression and the Dead Sea
The following account of the geology of the Dead Sea basin A. has been compiled from the observations of others, and I am especially indebted in this connection to H. J. Johnson, Geologist of the United States Expedition to the Dead Sea, to Professor Louis Lartet, Geologist of the Due de Luynes' Expedition to the same region, and to Prof. Edward Hull, F.R.S., Director of the Geological Survey of Ireland, who visited Arabia Petraaa and Palestine in 1883–84, under the auspices of the Committee of the Palestine Exploration Fund. Besides these observers, who devoted their attention specially to the geology of the regions traversed during their several expeditions, the writer is under obligations to the Ordnance Survey of Palestine, and to many observant travellers, including Condor, Fraas, Tristram, Wilson, and others, for many interesting details and attractive descriptions concerning the regions to which it is desired to direct the reader's attention.
Geological Magazine↗
VII.—On Hindeastraea, a New Generic Form of Cretaceous Astraeidae
The little Coral here described was discovered in Kaufman County, Texas, in strata of the Kipley Group, by Dr. R. H. Loughridge, and presented by him to me, together with a few characteristic molluscan species of that group which he found associated with it. The Ripley Group is the uppermost division of the Cretaceous series in the States which border upon the Gulf of Mexico; and probably represents approximately the Upper Chalk of England. Regarding it as a new generic form I herewith give a diagnosis and figures of it; and being the only species known to me, the diagnosis is necessarily based upon this alone.
Texas↗
II.-The Jordan-Arabah Depression and the Dead Sea
The occurrence of numerous terraces on the mountain slopes over-looking the Dead Sea has been reported by several observers, but no accurate measurements of their elevations or definite correlation of the terraces on the opposite slopes of the depression, seem to have been attempted. In the central part of the Wady Arabah on the west flank of the promontory known as Samrat el Fedan, a terrace, or perhaps more properly a gravel bar, has been observed by Hull at an elevation of about 1300 feet above the Dead Sea. This is apparently a definite record of the surface level of the Dead Sea during a former period. On the sides of the Jordan valley the terraces range in height from a few feet to 750 feet above the river. The measurements reported show great variation due principally to an inclination of the surfaces of the terraces, towards the centre of the valley, but indicating also that they are not horizontal in the direction of drainage.
Geological Magazine↗
IV.-Some Definitions in Dynamical Geology
In view of the active discussion of the problems of earth-movement and mountain-growth now current, certain fundamental definitions, growing out of the discrimination of processes commonly confounded but really distinct, seem to be timely. The various processes with which the geologist has to deal fall naturally into two principal and antagonistic categories and five subordinate and supplemental categories; and each category, great and small, comprises two antagonistic classes of movements or agencies.
Geological Magazine↗
III.-The Work of Prof. Henry Carvill Lewis in Glacial Geology
The recent notice of the life and work of Prof. Henry Carvill Lewis, whose lamented death occurred in Manchester, July 21st, 1888, in his thirty-fifth year, well indicates the wide range of his scientific labours. He published valuable results of investigations in astronomy, mineralogy and petrology, and especially in glacial geology, the last being based on his exploration of the drift and its terminal moraines in the United States, and later in Ireland, Wales and England. The present article reviews his contributions to our knowledge of these drift formations and of the history of the Ice Age, bringing into comparison and correlation the glacial records of America and Europe. Comprehensive as were Professor Lewis' observations and studies in this field, he was planning yet more thorough and extensive exploration of the drift in Britain, Germany and Scandinavia, when he was taken from us.
Geological Magazine↗
Mesozoic non-marine petroleum source rocks determined by palynomorphs in the Tarim Basin, Xinjiang, northwestern China
The Tarim Basin in Northwest China hosts petroleum reservoirs of Cambrian, Ordovician, Carboniferous, Triassic, Jurassic, Cretaceous and Tertiary ages. The sedimentary thickness in the basin reaches about 15 km and with an area of 560000 km2, the basin is expected to contain giant oil and gas fields. It is therefore important to determine the ages and depositional environments of the petroleum source rocks. For prospective evaluation and exploration of petroleum, palynological investigations were carried out on 38 crude oil samples collected from 22 petroleum reservoirs in the Tarim Basin and on additionally 56 potential source rock samples from the same basin. In total, 173 species of spores and pollen referred to 80 genera, and 27 species of algae and fungi referred to 16 genera were identified from the non-marine Mesozoic sources. By correlating the palynormorph assemblages in the crude oil samples with those in the potential source rocks, the Triassic and Jurassic petroleum source rocks were identified. Furthermore, the palynofloras in the petroleum provide evidence for interpretation of the depositional environments of the petroleum source rocks. The affinity of the miospores indicates that the petroleum source rocks were formed in swamps in brackish to lacustrine depositional environments under warm and humid climatic conditions. The palynomorphs in the crude oils provide further information about passage and route of petroleum migration, which is significant for interpreting petroleum migration mechanisms. Additionally, the thermal alternation index (TAI) based on miospores indicates that the Triassic and Jurassic deposits in the Tarim Basin are mature petroleum source rocks. ?? Cambridge University Press 2008.
Geological Magazine↗
The Pacific Northwest; linkage between earthquake and volcano hazards
AS the title of the magazine Earthquake and Volcanoes suggests, these two geological phenomena are often closely associated. Earthquakes frequently precede volcanic eruptions, and volcanoes are often sources of small to intermediate size earthquakes resulting from the movement of magma within the volcano's plumbing system. In the Pacific Northwest, the association between earthquakes and volcanoes is much more fundamental- they both arise from the same large-scale interaction between two plates of the Earth's crust. The oceanic Juan de Fuca plate is being shoved beneath the edge of the continental North American plate in the process known as subduction. The result is the Cascade chain of volcanoes, the potential for very large earthquakes along the coastal margin, and the generation of stresses that produce other regional earthquakes. The Pacific Northwest (Oregon, Washington, and northern California) is experiencing rapid industrial and population growth. The same conditions that make the region attractive- close proximity to both mountains and oceans, volcanoes and spectacular inland waters- also present significant geologic hazards that are easily overlooked in the normal timetable of human activities. The catastrophic eruption of Mount St. Helens 10 years ago serves as a dramatic reminder of the forces of nature that can be unleashed through volcanism. other volcanoes such as mount Rainier, a majestic symbol of Washington, or Mount hood in Oregon, lie closer to population centers and could present far greater hazards should they become active. Earthquakes may affect even larger regions, prodcuging more cumulative damage.
Pacific Northwest↗
Dwornikite, (Ni,Fe)SO 4 .H 2 O, a member of the kieserite group from Minasragra, Peru
A new nickel sulphate monohydrate is described from V-sulphide ore from Minasragra; it occurs associated with patronite (VS 2 ) with various sulphates, sulphur and bitumen. Dwornikite forms fine-grained white aggregates mixed with other oxidation products. Indexed X-ray powder data are tabulated; strongest lines 3.342(100) , 4.732(70), 3.024(70), 4.754(50), 3.293(35), 2.491(35) A; a 6.839, b 7.582, c 7.474 A, beta 117.85o; space group C2/c. XRF gave NiO 39.0, FeO 9.3, SO 3 42.4, = 90.7; D calc. 3.34 g/cm 3 ; mean refr. ind. approx 1.63. Unit-cell data for the synthetic end-member compounds NiSO 4 .H 2 O and FeSO 4 .H 2 O and new X-ray powder data for retgersite (NiSO 4 .6H 2 O) are given. The name is for E. J. Dwornik, mineralogist with the U.S. Geological Survey.-R.A.H.
Mineralogical Magazine↗
Effects of Cenozoic subduction along the outboard margin of the Northern Cordillera: Derived from e-book on the Northern Cordillera (Alaska and Western Canada) and adjacent marine areas
This article describes the regional effects of Cenozoic subduction along the outboard margin of the Northern Cordillera (Alaska, USA, and Western Canada), and thereby acquaints the reader with several chapters of the e-book Dynamic Geology of the Northern Cordillera (Alaska, Western Canada, and Adjacent Marine Areas) . This article and the e-book are written for earth-science students and teachers. The level of writing for the article and the source e-book is that of popular science magazines, and readers are encouraged to share this article with students and laypersons. The main thrust of the article is to present and describe a suite of ten regional topographic, bathymetric, and geologic maps, and two figures portraying deep-crustal sections that illustrate the regional effects of Cenozoic subduction along the outboard margin of the North American Cordillera. The regional maps and cross sections are described in a way that a teacher might describe a map to students. Cenozoic subduction along the margin of the Northern Cordillera resulted in the formation of the following: (1) underthrusting of terranes and oceanic lithosphere beneath Southern Alaska; (2) landscapes, including narrow continental shelves along Southern and Southeastern Alaska and Western Canada (the Canadian Cordillera) and continental-margin mountain ranges, including the Alaska Peninsula, Chugach Range, Saint Elias Mountains, and Cascade Mountains; (3) sedimentary basins; (4) an array of active continental strike-slip and thrust faults (inboard of subduction zones); (5) earthquake belts related to subduction of terranes and oceanic plates; (6) active volcanoes, including continental-margin arcs (the Aleutian, Wrangell, and Cascade Arcs) linked to subduction zones, and interior volcanic belts related to strike-slip faulting or to hot spots; (7) lode and placer mineral deposits related to continental margin arcs or subduction of oceanic ridges; (8) hot springs related to continental-margin arcs; (9) plate movements as recorded from GPS measurements; and (10) underthrusting of terranes and oceanic lithosphere beneath the Northern Cordillera.
Alaska, British Columbia, Idaho, Montana, Washingt↗
When water, gravity and geology collide: Firsthand observations of the impacts of the 2013 Colorado floods
No abstract available.
Colorado↗
Sequential decision making in computational sustainability via adaptive submodularity
Many problems in computational sustainability require making a sequence of decisions in complex, uncertain environments. Such problems are generally notoriously difficult. In this article, we review the recently discovered notion of adaptive submodularity, an intuitive diminishing returns condition that generalizes the classical notion of submodular set functions to sequential decision problems. Problems exhibiting the adaptive submodularity property can be efficiently and provably near-optimally solved using simple myopic policies. We illustrate this concept in several case studies of interest in computational sustainability: First, we demonstrate how it can be used to efficiently plan for resolving uncertainty in adaptive management scenarios. Secondly, we show how it applies to dynamic conservation planning for protecting endangered species, a case study carried out in collaboration with the US Geological Survey and the US Fish and Wildlife Service.
AI Magazine↗