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In the following list, brief‐statements have been added to certain references to call attention to special phases of ground‐water problems which are not apparent from the titles. Abstracts of most of the papers have been or will be published in the Annotated Bibliography of Economic Geology.
The membership of this Committee is as follows: C. S. Howard, Chairman, U. S. Geological Survey, Washington, D.C. D. G. Thompson, U. S. Geological Survey, Washington, D.C. A. C. Lane, 22 Arlington Street, Cambridge, Massachusetts C. S. Scofield, Bureau of Plant Industry, U. S. Dept. Agri., Washington, D. C. I. A. Denison, U.S. Bureau of Standards, Washington, D.C. T. G. Thompson, University of Washington, Seattle, Washington W. P. Kelley, Citrus Experiment Station, Riverside, California In order to provide for close cooperation between the work of the different research‐committees of the American Geophysical Union it was decided to have the chairmen of certain committees serve on other committees. The Chairman of the Committee on the Chemistry of Natural Waters is serving on the Committee of Underground waters and D. G. Thompson as Chairman of the Committee on Underground Waters is serving on the Committee on Chemistry of Natural Waters
Two meanings are unfortunately given to the term geophysics. In the broad sense, based on the etymology of the term, geophysics means the physics of the Earth. This is its significance in the names “Geophysical Laboratory of the Carnegie Institution of Washington,” “International Union of Geodesy and Geophysics,” and “American Geophysical Union.” In this sense the sciences of geology and hydrology are largely geophysics, although in part they are geochemistry or biology. Geologists and hydraulic engineers who are elected to membership in the American Geophysical Union are, however, often surprised to find that they are regarded as “geophysicists.” I hope that when the Union establisnes a journal, its name will include the expression “Earth physics” or “Physics of the Earth,” in order that there will be no misunderstanding as to its scope.
In the course of a systematic survey of the ground‐water resources of the Hawaiian Islands which is being made under the direction of H. T. Stearns of the United States Geological Survey in cooperation with the Territorial Government of Hawaii, it was found desirable to test the utility of geophysical methods in the solution of certain Hawaiian water‐supply problems. A cooperative geophysical survey for this purpose was undertaken by the Geophysical Section, then with the Bureau of Mines but later transferred to the Geological Survey, during the course of which a series of resistivity‐studies of certain salt‐water boundaries was begun. Since the location of such boundaries is of considerable importance in many areas it has been thought worth while to present the results which have thus far been obtained.
During 1935 and 1936 the Ground‐Water Division of the United States Geological Survey made an investigation of the ground‐water resources of the El Paso, Texas, Area. Geological and hydrological studies comprised the principal part of the investigation, and these studies were supplemented by measurements of earth‐resistivity made largely by the Geophysical Section of the Geological Survey along traverses aggregating 51 miles. The extent to which resistivity‐methods may be useful in ground‐water work has been the subject of much discussion. A full evaluation of the method can not be made at this time. However, the work in the El Paso Area indicates that the presence of faults and of underground bodies of salt water may be definitely determined by resistivity‐measurements.
The work described in this paper was all done in connection with dam‐site investigations and was not directly connected with hydrology. However, geophysics is coming to have a place in hydrologic investigations, and these results may throw some light on what can be accomplished by resistivity‐measurements. We have found that,for many questions not involving exact determinations of depth, resistivity‐ measurements give conclusive answers. Ordinarily a reliable answer can be expected to the question of the existence of a buried channel if the covering is composed of unconsolidated material with a resistivity differing from that of the rock. For example, topographic surveys were made at two alternative dam‐sites on a river about four miles apart. Examination of the surface‐geology indicated that a channel burled under glacial debris possibly existed at each site, but resistivity‐measurements proved that such a channel existed at one site and not at the other. On the other hand, at another site the geologist suspected there might be an old channel on a steep side hill. Geophysical measurements showed a depth of overburden of 46 feet and showed that if a deeper channel exists it must be narrow; but they did not show positively that no such channel exists. Probably a careful survey with a large number of lines would have given a more definite answer, but the rough topography interfered with the resistivity‐work, and time and money were not available for a detailed survey. After completion of the geophysical work, the geologist located some outcrops which led him to conclude that no old channel exists at this site. At two other dam‐sites in Oregon resistivity‐measurements showed that there were no burled channels.
The withdrawal of water from a well necessarily produces a drop in water‐level in the well. The ground‐water level in the vicinity of the well from which the water is withdrawn likewise declines, but the amount of decline decreases with increasing distance from the well, so that a cone of depression of the water‐surface in the vicinity of the well is produced. The cone of depression is an actual water‐surface if the ground‐water is not confined under pressure. If the ground‐water is under artesian pressure, the cone of depression is a depression in the piezometric surface. If the cones of depression of two or more wells ending in the same formation overlap, interference of the wells occurs. In this case (the combined yield of the wells when pumped simultaneously will be less than the sum of the individual yields if the wells are pumped separately. In choosing the proper spacing of wells from the operator's point of view, it is important to know the lateral extent of the cones of depression of supply‐wells ending in a given formation. In many installations two or more wells are so closely spaced that their mutual interference is excessive.
In common with many of the arid and semiarid States, the prosperity of Utah probably is more dependent upon the amount of water available than upon any other natural resource. Although only about four per cent of the State is irrigated, a shortage of water for irrigation becomes a major calamity. A large part of the water‐supply for the State is derived from surface‐streams, but a most valuable supplement to this supply is the water available from underground sources. Ground‐water is used extensively for domestic, stock‐watering, and industrial purposes as well as for irrigation. The primary source of the municipal water‐supply for Salt Lake City is from streams entering the Jordan River Valley from the western slope of the Wasatch Mountains. However, since the drought‐year of 1931, a supplementary municipal supply has been obtained from ground‐water, and, among the 17 wells developed by the City during the extreme drought of 1934, one—yielding about ten cubic feet per second, or 4500 gallons a minute—is probably the largest in the State. Ogden, the second largest city in Utah, with a population of about 40,000, obtains the major part of its municipal water‐supply from a group of artesian wells in Ogden Valley about 12 miles east of the City. A considerable part of the water‐supply for the City of Brigham is obtained from wells. Springs constitute the source of most of the water‐supply for Logan, Provo, and many smaller towns and localities in the State. In nearly every developed area of the State ground‐water is used for some purpose, and in some areas the water‐supply is obtained almost entirely from wells.
For the last six years the United States Geological Survey, in cooperation with the State Engineer of New Mexico, has been making somewhat intensive studies of ground‐water in the part of the High Plains that lies in New Mexico, and in 1933 and 1934 the Geological Survey, with funas allocated by the Public Works Administration, made an extensive reconnaissance‐survey of the ground‐water conditions in the southern High Plains. These studies have resulted in considerable data that throw much light on the quantity of recharge to the ground‐water in this area. An estimate of the quantity of recharge is of immediate value for this area, because the use of ground‐water is constantly being increased. In addition, it has a general value in serving as a criterion for estimating recharge in other areas in the Southwest for which fewer data are available. Estimates of the recharge in the High Plains as previously made without the advantage of quantitative data have ranged from less than three or four inches a year [see 1 of “References” at end of paper] to less than six inches [2]. The work of the last few years indicates they should be greatly reduced.
The oldest igneous rocks in the Comstock District are amphibolites probably derived from basalts and of Triassic age. These are intruded by pre‐Tertiary quartz monzonlte and by granodiorite of Sierran facies, the latter not being exposed on the surface but found on mine‐dumps. Igneous activity recorded mainly in volcanic rocks was almost continuous throughout the Tertiary. Its products, in order of age, were as follows: Eocene—Rhyolitic flows aggregating a few hundred feet in thickness: One intrusive plug of rhyolite occurs. Eocene or Miocene—Hornblende‐auglte andesite intrusive into the rhyolite, type locality American Ravine. ©1938. American Geophysical Union. All Rights Reserved.
The igneous rocks and the minerals of Magnet Cove, Arkansas, have long interested geologists and mineralogists, but in much of the area rock‐exposures are so sparse that many of the geologic, relations have remained obscure. However, recent prospecting and the mining of titanium ores have uncovered rocks that throw new light on the geology of the region. The regional rocks of the area are sandstones, slates, and novaculite of Paleozoic age. They were folded and underwent metamorphism in late Paleozoic time. In Cretaceous time they were intruded by a series of igneous rocks. ©1938. American Geophysical Union. All Rights Reserved.
Two of the numerous small dikes mapped on the areal geology sheet of the Franklin Furnace Folio (U.S. Geological Survey 161) as “Mostly basic, including nepheline tinguaite, leucite tinguaite, and camptonite” of post‐Ordovician age, have been found to be quite distinct from these alkalic rocks, and the two dikes in question are indistinguishable from the Triassic diabase found elsewhere in New Jersey and adjoining States. The association of diabase with highly alkalic rocks has been observed and commented on by numerous writers. There is evidence pointing to the post‐Triassic age of the Beemerville alkaline rocks, and a possible correlation with a volcanic ash of Cretaceous age found by Stephenson and Carter at Haddonfield, New Jersey, near Camden, in 1936. ©1938. American Geophysical Union. All Rights Reserved.
During the last five years ground‐water has been more and more extensively used for air‐conditioning on Long Island, New York. The wide‐spread occurrence of highly permeable water‐bearing material and the relatively small cost of installation and operation of a ground‐water, air‐conditioning system has resulted in many such installations by theaters, restaurants, stores, and other establishments. Many companies likewise have taken advantage of these favorable factors and are utilizing low‐temperature ground‐water for cooling purposes in the manufacture of ice. This new use of ground‐water has considerably increased the draft in the western end of Long Island where there had already been so much over‐development that the watertable was below sea‐level in an area of more than 40 square miles. In 1933 the State Legislature, recognizing the seriousness of this over‐development, passed a law requiring that the approval, of the State Water Power and Control Commission be secured before constructing a well with a capacity greater than 100,000 gallons a day. Since the passage of the law the‐policy of the Commission has been to require water pumped from new‐wells for cooling purposes to be returned to the ground. This requirement has resulted in the construction of many recharge‐wells (locally called diffusion‐wells) through which the warm water is returned to the ground.
As time marches on, historians are usually quite faithful in recording the activities of man, and it will usually be found that Mother Nature is even more meticulous in reflecting and preserving her experiences, more especially with regard to climate and vegetation. Just how much the activities of man have done to modify the natural conditions of a virgin country may in some respects always remain a question. There is however, no longer the slightest doubt about the influence civilization may have had on the climate—which is none at all! And it is the purpose of the present paper to introduce a few trustworthy witnesses in support of the hypothesis that the activities of man have also been ineffective with respect to noteworthy changes in the general aspect of the native vegetation, outside the ranch‐fences of the West.
The instrument herein described was originally designed and built to record the evaporation‐loss from a standard Weather Bureau pan for use in a study of the variation of flow in Santa Ana River. Valuable suggestions were made by various members of the Water Resources Branch of the Geological Survey in Southern California, and financial assistance for construction was given by F. C. Ebert and H. C. Troxell of the same organization. The typing of the paper and some of the drafting were done by Works Progress Administration help. The original instrument was damaged by flood‐waters in 1934, while in operation at Baldwin Park, California. It was then redesigned and constructed of stainless materials and installed on the campus of the San Bernardino Valley Junior College. The Weather Bureau pan was replaced by a thermally insulated pan. The damping unit was added at this time by the present writers. The evaporimeter was placed in regular operation on October 30, 1937, in a study of the relative magnitudes of the various energy‐components associated with solar and sky radiation and with evaporation from water‐surfaces, from damp soil, and from plants.
In this informal paper the processes of snow‐wastage at high altitudes were discussed and a number of slides illustrating suncups and sunpits in different stages of development were shown. It was stressed that these features are peculiar to the region above the timber‐line, which biologists term the Alpine, or Arctic‐Alpine, Zone. That regions is, as a matter of fact, primarily and fundamentally a physiographic zone distinct from all other physiographic zones at lower levels by reason of an unusual combination of climatic, hydrologic, and geologic factors.
The High Plains region has been passing through a prolonged low in the precipitation‐cycle during a large part of the last decade. The drought has continued longer and has been more severe than any that has been experienced since the region began to be farmed. It has caused untold distress. Crops have failed for years in succession. In large areas in the so‐called dust‐bowl the top soil has been almost entirely removed by wind‐erosion and the dust‐storms have become so bad at times that the health of the inhabitants has been seriously threatened. In some parts of the region the annual rainfall, which ranges from about 18 to 24 inches, according to the location of the area, has returned to about the normal or long‐time average. In others the drought is still in progress and a partial or complete crop‐failure was again experienced in 1938. When the rainfall‐record is studied, it becomes apparent that a large part of the High Plains never should have been farmed and should be allowed to go back to the range, if indeed the native grasses can be restored. Other parts, however, can still be farmed with moderate success by the farmer who uses proper methods of cultivation and crop‐rotation, and combines farming with stock‐raising by keeping a part of his land in pasture and raising mostly feed‐crops. Irrigation, if it can be accomplished at a practicable cost, affords security both to the farmer and stock‐raiser.
In the prediction of spring runoff from precipitation‐records or snow‐surveys, one of the factors which seems to require consideration is the amount of water held in ground‐storage. The determination of the quantity of water in ground‐storage is a difficult problem involving soil‐sampling, measurements of ground‐water wells, and measurements of the flow of small streams and springs. It has occurred to the writer that selected stream‐flow records for either the late fall or early spring might provide a better index of the ground‐water available for spring runoff than that obtained by other methods. This would involve a comparison of runoff in the fall with runoff in the spring, and might eliminate uncertainties in the relation of a reservoir‐level in the fall with runoff in the spring. Such a method would be especially desirable because of the availability of stream‐flow records. The discussion which follows is more an explanation of the method to be used than an attempt to develop an accurate formula for the prediction of spring runoff.