摘要:

The American Geophysical Union was established in 1919 as the American Committee of the International Union of Geodesy and Geophysics, and its Executive Committee is the Committee on Geophysics of the National Research Council. The objects of the Union are to promote the study of problems concerned with the figure and physics of the Earth, to initiate and coordinate researches which depend upon international and national cooperation, and to provide for their scientific discussion and publication. In the accomplishment of these objects, the Union is divided into sections following the plan of organization of the International Union of Geodesy and Geophysics. There are now seven sections, namely, (a) Geodesy, (b) Seismology, (c) Meteorology, (d) Terrestrial Magnetism and Electricity, (e) Oceanography, (f) Volcanology, and (g) Hydrology. A Section of Geophysical Chemistry was discontinued May 31, 1924, as the International Union had failed to provide such a Section; the Section of Hydrology was established November 15, 1930—matters pertaining to scientific hydrology referred to the American Geophysical Union had been previously looked after by special committees on Hydrolog

ISSN:0002-8606    

DOI:10.1029/TR019i001p00003

年代:1938

数据来源: WILEY

摘要:

In introducing a constructive discussion of the physics of volcanic processes it will suffice to provide a very brief historic background against which the distinguished students of this subject, who will follow me, may present the current status of such studies and the outlook for the future.In a volume entitled “Das Magma und seine Produkte” [ I . Tell, Leipzig, 1937], which is just off the press, Dr. Paul Niggli has given a most interesting resume of the long record of experimental efforts to elucidate these processes. The speculations of the early Greeks, who sought to explain the activity of Etna, and their Italian successors beginning with Pliny's description of the eruption of Vesuvius in 79 A.D., have brought us little actual evidence that is useful today. They do not go beyond the effort to reconcile the supposedly incompatible activities of the primitive elements air and fire and water, and the earlier accounts are rather highly flavored with instances of arbitrary interference by the G

ISSN:0002-8606    

DOI:10.1029/TR019i001p00008

年代:1938

数据来源: WILEY

摘要:

The phenomenon of volcanic activity has occupied the attention of observers throughout the ages and will continue to do so if for no other reason than to try to satisfy our curiosity as to the cause of this outward expression of the forces beneath the Earth's crust and therefore removed from direct observation. The extrusion of hot materials either solid or fluid is our only direct evidence that what we call igneous rocks were once molten. It seems obvious, therefore, that if the study of the extruded lava and its related products can be coordinated with laboratory‐investigations we shall have taken a step in the direction of finding that much‐ought‐for logical generalization as to the cause of volcanic act

ISSN:0002-8606    

DOI:10.1029/TR019i001p00010

年代:1938

数据来源: WILEY

摘要:

A geologist describes the structure of volcanic heapings for interpretation of history. A geophysicist,describing structural development, has in view the basis of experience for forecasting evolution of construction that is to come, in a living volcanic edifice.A volcanologist in Hawaii observes changes in the structure of a volcano by direct experience. He watches the addition of gushes of gas and of extruded magma from within the so‐called crust of the Eart

ISSN:0002-8606    

DOI:10.1029/TR019i001p00023

年代:1938

数据来源: WILEY

摘要:

The sites of volcanoes or of volcanic regions are not restricted to any single type of local or regional geologic structure. It is true that many volcanoes are distributed along linear belts where the Earth's crust has yielded to great crustal stresses, as for example in Iceland, central France, our own Cascade Range, and along the Gulf Coast. The ancient volcanoes of the Gulf Coast were located along a belt of folded sedimentary rocks, known as the Ouachita Belt [see 1 of “References” at end of paper], presumably a belt of weakness, that served as a hinge line during downwarplng of the Gulf Coast in Upper Cretaceous time, in parts of the Great Basin of Nevada and California the great faults that broke the crust into huge basin‐ and range‐blocks exerted some control over the location of the volcanic activity, cones having been built along some of the faults. Yet such faults are only a local factor in the location of volcanoes because other volcanoes drilled their way through the massive granite of the Sierra Nevada independently of faults and erupted at much greater elevations than along the fau

ISSN:0002-8606    

DOI:10.1029/TR019i001p00032

年代:1938

数据来源: WILEY

摘要:

Although explosion may initiate volcanism of the type represented at central vents, it is not essential for continued activity. Nor is such violent action necessary even for the opening of central vents, as shown by the pit‐craters of Hawaii. These are genuine volcanic vents and yet are not rimmed with ash, tuff, or breccia, the normal products of explosion. On the other hand, the pit‐craters, like Kilauea and many other craters on islands and continents, were opened and kept open by fluxing magmatic gas, rising quietly. Quiet emanation of gas is the essential part of the mechanism that gives prolonged activity. But emanation from what? This is the ineluctable, chief problem of volcanology. The root of the volcano is the root of the mat

ISSN:0002-8606    

DOI:10.1029/TR019i001p00035

年代:1938

数据来源: WILEY

摘要:

I am glad to avail myself of the opportunity afforded by your Committee on Meetings to make a brief summary of the program. This Symposium has provided a splendid outlook on the problem of volcanology and, without doubt, has clarified the subject in the minds of those who have been fortunate enough to be present this afternoon. In the time available it is probably not possible to make an adequate summary, but I should like to make a few general comments at this time and to recall the scope of the program.

ISSN:0002-8606    

DOI:10.1029/TR019i001p00039

年代:1938

数据来源: WILEY

摘要:

For some time I have been interested in a study of the place of surveying in its different branches in the curricula of American colleges and universities, particularly as it is taught to students in civil engineering. About two years ago, I examined the catalogues of a large number of the principal engineering schools and made a tabulation of the number of credit hours devoted to surveying.It was found that there is a great variation in the names of the courses, in the subject‐matter covered, and in the distribution of it throughout the curricula. In spite of this variation we may consider that most of the courses offered might have been entitled by one of the following designations, or by what I might call type‐names for courses: Elementary surveying; advanced surveying; topographical drawing; route surveying; practical astronomy; least squares; geodesy; photographic surveying; and summer sur

ISSN:0002-8606    

DOI:10.1029/TR019i001p00046

年代:1938

数据来源: WILEY

摘要:

Eight years ago the Naval Observatory was broadcasting time three times daily, with an average error of from 0.03 to 0.05 second. Like all other time‐determining observatories in the world, time was determined by visual observations of the transits of stars over the meridian of the Naval Observatory.During the past eight years the Naval Observatory has gained a reputation for its accuracy and its cooperation. One of the European authorities, in an official report listing the various fundamental observatories in the world in accordance with their accuracy, rated the United States Observatory 100 per cent, while the various observatories in Europe and South America were tabulated with varying percentages of accuracy. The nearest competitor was Potsdam shown with 100 on its right‐ascension work, but only 70 per cent on its declination‐work. This institution received 100 per cent on both. About that time, the French Government also gave us an excellent rating on our time‐

ISSN:0002-8606    

DOI:10.1029/TR019i001p00048

年代:1938

数据来源: WILEY

摘要:

Precise or first‐order leveling, as it is now called, was first undertaken by the United States Coast and Geodetic Survey in 1878 when field‐work was begun on the line of levels of high precision which was to follow the general trend of the Transcontinental Arc, an arc of triangulation extending across the United States from Chesapeake Bay to the Golden Gate and following approximately the 39th parallel. From this single‐line beginning, the control‐leveling of the Survey has been extended until the fundamental leveling net now includes more than 260,000 miles of first‐ and second‐order leveling. About two‐fifths of this is first‐order leveling, the remaining three‐fifths being second‐order or s

ISSN:0002-8606    

DOI:10.1029/TR019i001p00051

年代:1938

数据来源: WILEY