Cave Notes

Cave Notes

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Cave Notes
Series Title:
Caves and Karst: Research in Speleology
Alternate Title:
Caves and karst: Research in speleology
Cave Research Associates
Cave Research Associates
Tumbling Creek Cave Foundation
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Content: Cave detection by geoelectrical methods, part I: resistivity / J. G. Day -- Proceedings -- Annotated Bibliography. Cave Notes(vols. 1-8) and Caves and Karst: Research in Speleology(vols. 9-15) were published by Cave Research Associates from 1959-1973. In 1975, the Tumbling Creek Cave Foundation compiled complete sets of the journals in three volumes. The Foundation sells hardbound copies of the material to support its activities.
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Tumbling Creek Cave Foundation Collection
Original Version:
Vol. 6, no. 6 (1964)
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CAVE NOTES A Review of Cave and Karst Research Volume 6, No.6 November/December, 1964 CAVE DETECTION BY GEOELECTRICAL METHODS, PART I, RESISTIVITY' by J. G. Day Methods of electrical cave detection are all based on the assumption that the electrical properties of a cave differ from those of the surrounding medium. This assumption is generally valid. with the possible exception of caves entirely filled with mud or water. which must be considered separately. Because most caves of speleological interest originate as solution cavities in limestone, dolomite, marble, or gypsum. this article is concerned primarily with the detection of such caves. However, the electrical detection of other types of caves, such as lava tubes. differs rnainly in quantitative rather than qualitative respects. The presence of a subsurface void constitutes an abrupt electrical di a-. continuity with respect to the surrounding rne di um For our purposes, a cave can be considered as a region of infinitely high d. c. resistance. The simplest way to detect a void by e lectrical means is by its effect on local resistivity meaaur ements The resistivity of any substance is equal numerically to the ohmic resistivity of a one ~ centimeter cube of the substance. measured between two paral~ Le l faces. Re ai a-. tivity is determined by the formula p ;;0 RAIL, where R is the measured resistance of a conductor in ohms; A, its cross-sectional area GNEISS 10' 10' 10' 10' 10' BASALT ClAY COAL w4% CONGLOMERATE GRANITE lAVA LIMESTONE MARBLE QUARTZITE SALT SANDSTONE SCHIST sHALE SlATE Figure 1. Rock resistivity ranges in meter-ohms. *These summary articles on electrical methods of cave detection should answer the needs of those readers who seek a basic review of a subject now receiving considerable emphasis, Readers are invited to contribute results of specific geophysical experiments 'in karst, to follow these introductory discussions. 41


CAVE NOTES CAVE NOTES CAVE NOTES is a publication of Cave Research Associates and the Cave Research Association. Subscriptions are available for $2.00 per year (six issues) or on exchange. Mid-year subscriptions receive the earlier numbers of the volume. Correspondence, contributions, and subscriptions should be addressed to: CAVE RESEARCH ASSOCIATES, 3842 Brookdale Blvd, Castro V~lley, Calif. Editor: Arthur L. Lange, Cave Research Associates Associate Editor: Ronald A. Brandon, Cave Research Association (Dept. of Zoology, Southern Illinois University, Carbondale, Illinois) Managing Editor: R. deSaussure, Cave Research Associates. ~ Copyright 1964, Cave Research Associates. in square centimeters, and L, its length in centimeters. The electrical properties of soils must be taken into account in resistivity surveys, because the soil between the sensors and the region of interest may greatly influence the flow of current or propagation of electromagnetic waves in the vicinity. A wide variety of materials is included in the general c lae sification of soil (Lyon, et al., 1952). For the purposes of this article, soil is considered to consist of all of the material between the surface of the earth and bedrock. With regard to moisture, soil can be thought of as comprising three layers, or zones: the r-h iz i c generally extending less than one meter below the surface; the ar-gic or intermediate zone; and the p'le r otdc which extends from the argic to bedrock (Meinzer, 1939). If the water-table lies below bedrock, the plerotic soil zone is absent. The r-hi.z i c zone is characterized by an abundance of organic detritus and may be very moist for several days after a rain. The argic zone contains less organic matter than the rbtz ic and water percolates downward through this zone toward the phreatic surface of the plerotic zone. The size and arrangement of particles and the presence of organic matter control the size and number of pore spaces which can hold water. A soil with a low density has a large amount of pore space which can be filled with water. However. the amount of water which a soil will retain against gravity depends not only on the total amount of pore space. but also on the size of the individual pores. A sandy soil with large soil particles has large pores which drain easily. A clay soil has not only a greater total pore space, but also the ability to retain a much greater amount of water against the pull of gravity. Another variable affecting soil resistivity is the amount and type of soluble substances present. A soil may have a high or low resistivity, depending on the presence or absence of lime, alkalies, and other materials. Water can exist in the soil in any of three forms: hygroscopic moisture adsorbed on the surfaces of soil particles, capillary moisture held in the soil pores against the pull of gravity, and gravitational water which tends to drain to the level of the local wate r c tab le The amount of water remaining in the eoi.l with the gravitational water removed has a great effect on 42


VOLUME 6, NO. 6 soil resistivity. The resistivity of rain-water ranges from less than 50 to rno r-e than 1000 meter-ohms, while soil-water resistivity varies between one and 100 meter-ohms, depending on the chemical composition of the soil. The resistivity of moat soils, including moisture, ranges from one to 100 meter-ohms, 1 0 mete r e ohms being a typical value for a moist soil. Soil resistivity depends. to some extent. on soil temperature; the highest resistivities are those of soils which are frozen to a considerable depth. Rock resistivities vary over the ranges shown in Figure 1. and tend to increase with depth. Igneous rocks are usually more resistive than most sedimentary or metamorphic rocks (Card, 1935). In most areas of the United States, the basement complex of primarily pre-Cambrian igneous and metamorphic rocks has resistivities of the order of 1000 to 10,000 meter-ohms. The resistivities of most types of rock between the basement complex and the surface, or the rock-soil interface. range between 100 and 1000 rnete r c chrns The water contained in the pores of igneous rocks has an average resistivity of 100 meter-ohms; while that contained in sedimentary rocks may measure less than one meter-ohm. The resistivities of limestones and marbles vary over a wide range. Dense limestones, such as Solenhofen limestone, are compo eed almost entirely of calcite and us ually have a porosity of a few tenths of a percent and a resistivity well over 10.000 meter-ohms. Porous limestones, such as Spergen limestone. may have resistivities of less than 100 meter-ohms. in situ. depending on water content and conductivity. In making resistance measurements of most ordinary electrical circuits. one usually employs a simple ohmmeter equipped with two electrode probes. If one attempted to measure the resistivity of a block of limestone in this way. the reading obtained would not be accurate because of the relatively small area of contact between the probe tips and the poorly conducting rock surface. There are two ways of overcoming this difficulty: the use of probes having suitably large contact areas. and the use of some alternative method of me as ur ement which is inherently not subject to this difficulty. The first approach is sometimes resorted to, but the second is generally preferable. One means of avoiding errors in resistivity measurements is the use of four e lectr-ode s instead of only two. Two of these are designated "cur-rent" electrodes, and the other two, "potential" {i e . voltage) electrodes. If the resistive substance has a fairly flat surface and is reasonably homogeneous, then it does not matter. in principle, what the spacings or geometrical relationships of the four electrodes are, so long as the distances between them can be measured. Figure 2 shows such an arrangement of four randomly placed electrodes. The current electrodes, A and B. are connected in series with a source of current and an ammeter. The potential electrodes, F and G are connected to a sensitive. high-resistance voltmeter. The potential me aaured between F and G. together with A ~ --------D' G ...0----------, \ I \ I ~i \ Dz D, I \ I I \ \ ? \ ,.../,... B \ D, F ~//,...,... E}-----' Figure 2. Arbitrary electrode arrangement. 43


CAVE NOTES the known current I through A and B, and the measured distances between the current and potential electrodes, can be used to calculate the resistivity of the rock mass, p It is more convenient to arrange a regular geometrical pattern, to the current and potential electrodes in simplify resistivity calculations. The Wenner arrangement, illustrated in Figure 3, is the one most commonly used (Wenner, 1916). Using this configur-ation, resistivity can. be calculated by the formula, P = 2'lDE/I I E A 8 F I To counteract the undesirable effects of electrolytic polarization, it is advantageous to use either commutated direct current or alternating current. When commutated direct current is used, the common practice is to commutate [i e , reverse) the potential electrodes in synchronism with the current electrodes, so that a d-e voltmeter can be used (Gish and Rooney, 1925). If alternating current is applied to the current electrodes, an a-c voltmeter and an a-.c ammeter must be employed. The use of alternating current in resistivity measurements introduces many additional considerations. Although its use is sometimes less efficient than that of direct current in terms of power required, this is often more than compensated for by the advantages derived. In particular, it is an advantage to be able to control the depth of r e stattvtty sensing by selecting an appropriate operating frequency (Peters and Ba.r deen, 1932). Very low frequencies penetrate the e ar th to much greater depths thajr do high frequencies. However, relatively high frequencies can provide better resolution of resistivity anomalies close to the surface. When an a-c resistivity survey is made of an area where sub-e urface voids are suspected, resistivity measurements are made at regular intervals along a number of parallel traverses, and a chart of relative apparent r esistivities is plotted. It is not necessary to calculate absolute resistivity values, as the variation in apparent resistivity is adequate to show any anomalies. It is, however, desirable to use the same a-.c frequency and electrode spacing for each station of a survey (When a constant depth of sensing is desired), otherwise the apparent resistivity may vary even in the absence of true anomalies. It is also desirable to use the same a-.c current value at each station, so that the voltmeter readings will be a direct Indication of relative apparent resistivity. Figure 3. Wenner electrode arrangement. When frequencies below 500 cps are used, the depth of sensing can be assumed to be roughly equal to the inter-electrode spacing. By making not just one resistivity measurement at each station, but several, each with a different inter-electrode spacing, it is possible to obtain a profile of resistivity versus depth at each station. Such profiles can be interpreted by comparison with master curves which have been plotted for models of a 44


VOLUME 6, NO. 6 mul.ti -Iaye r ed earth (Tagg, 1934). Mooney and Wetzel (1956) have published an album of 2400 such curves and a book of tables of potential values for typical combinations of layer thickness and resistivity. This album contains 20 two-layer, 350 tb ree-daye r and 2030 four-layer curves. Theoretical models have also been developed for dipping beds (Van Nostrand and Cook, 1955), vertical discontinuities (Logn, (954). and filled sinks (Cook and Van Nostrand, 1954). An extremely useful variation of the fundamental resistivity technique is one which maintains a constant ratio between the inter-electrode distances of the potential and current electrodes as the array is "expanded" at a station. This greatly simplifies cave depth determinations, since the actual depth can be obtained from the product of the apparent depth and the square root of the inter-electrode distance ratio (palmer, 1954). References: CARD, R. H. Earth resistivity and geological structure. Electrical Engineering, vot 54, p 1156. 1935. COOK, K. L., and R. G. VAN NOSTRAND. Interpretation of resistivity data over filled sinks. Geophysics, vol. 19, p. 761-790. 1954. GISH, O. H., and W. J. ROONEY. Measurement of resistivity of large masses of undisturbed earth. Terrestrial Magnetism and Atmospheric Electricity, vol. 30, p 161-188. 1925. LOON, 0, Mapping nearly vertical discontinuities by earth resistivities. Geophysics, vol. 19, p. 739-760. 1954. LYON, T. L" H, 0. BUCKMAN, and N. C. BRADY. The Nature and Properties of Soils. MacMillan Go" Ne~ York. 1952. MEINZER, O. E. Discussion of Question No. 2 of the International Commission on Subterranean Water: definitions of the different kinds of subterranean water. American Geophysical Union, Trans.) part 4, p. 674-677. 1939. MOONEY, H. M., and W. W. WETZEL. The Potentials ~!. Point Electrode ~ Apparent Resistivity Curves for !. Two-, ~, and Four-Iayer~. Univ. of Minnesot,a Press, 146p. 1956. PALMER, L. S. Location of subterran~an cavities by geoelectrical methods. Min~ ~., vot 91, no. 3, p. 137-141. 1954. PETERS, L, J" and J. BARDEEN. Some aspects of electrical prospecting applied in locating oil structures, Physics, vol. 2, p. 103-122, 1932. TAGG, G. F. Interpretation of resistivity measurements. (in American Institute of Mining and Metallurgical Engineers: Geophysical Prospecting) p. 135-145. 1934. VAN NOSTRAND, R. G., and K. L. COOK. Apparent resistivity for dipping beds--a discussion. Geophysics, vol. 20, p. 140-144, 1955. WENNER, F. A method of measuring earth resistivity. U.S. ~ of Standards, ~., vc L, 12, p. 469-478, 1916, * * * PROCEEDINGS Secretarts note: The annual rneettng of the Board of Trustees of Cave Research Associates was held at headquarters on October 1 J 1964. Officers elected for the cal.en45


GAVE NOTES dar year 1965 are as follows: President: Secretary: Arthur L. Lange George D. Mowat Vice-President: Thomas Aley Treasurer: Wilmer B. Martin New as eo c ia te s elected for the year 1965 are the following: George Goddard, Stanford, California Phil Pennington, Berkeley, California Lou R. Goodman, NUrnberg, Germany Peter Huntoon, Tucson, Arizona Louis A. Payen, Sacramento, California. ANNOTATED BIBLIOGRAPHY BAUER, FRIDTJOF. Kalkabtragungsmessungen in den osterreichischen Kalkhochalpen. Erdkunde, vol. IS, no. 2, p. 95-102. June 1964. Extrapolation from analyses of runoff from small test areas danuned by paraffin walls indicates that bare limestone in the Alps dissolves at a rate of 10 cm/10;OOO years, while soil-covered areas dissolve at 30 cm/l0,OOO years. --G.W.M. BVGLI, ALFRED W. The exploration of Hell Hole. The Mountain World 1962/63, Rand-McNally and Co., Chicago, p. 6-18. 1964. (Editor: Malcolm Barnes). A total of 47% miles of passage have now been mapped in the world's largest known cave, HCllloCh, Switzerland. The water table in the cave slopes approximately 25 feet per mile, and the water flows at an average rate of 1. 7 feet per minute. Determinations of dissolved solids in the water indicate that the cave is growing by about 500 cubic yards a year. --G.W.M. EdGLI, ALFRED. Mischungskorrosion--Ein Beitrag zum Verkarstungsproblem. Erd!wnde, vol. 18, no. 2, p 83-92. June 1964. Two calcium bicarbonate solutions, each possessing a different CO 2 partial pressure, and each saturated with CaC0 3 will produce an undersaturated solution when mixed. If saturated water with a high CO 2 content moves downward from the soil zone and encounters saturated ground water with a low CO 2 content, caves can be formed, despite the fact that neither solu~ion was able to dissolve additional limestone before being mixed. --G.W.M. CHIUSUEN, TSENG. Some problems pertaining to the classification of relief types in the karst region of South China. Acta Geologica Sinica, vol. 44, no. 1, p 119-129. 1964. Sub-classifications are offered for the following features: Lapiez, avens, depression areas, blind valleys, karst gorge characteristics, U-shaped valleys, corrosion plains (Karstrandebene), rock-peaks, horizontal caves (including a very rough speleothem breakdown), and corrosion relief forms. The primary value of the paper is probably the description and implications of this karst. --R.D. CROCE, DARIO. Sella Group. Cryonival phenomena and karst phenomena in the plateau of the Erdkunde, vol. 18, no. 2, p. 146-148. June 1964. Freeze-thaw action tends to oppose disrupting the surface. karstification in Alpine environments by --G.W.M. DELEURANCE, S., and E. DELEURANCE. L'absence de cycle saisonnier duction chez les insectes Coleopteres troglobites (Bathysciines et Paris Academie des Sciences, Comptes Rendus, vol. 258, no. 24, p. June 15, 1964. de repro'rrecnmes). 5995-5997. Examination of the ovaries of troglobitic beetles from natural environments, 46


VOLUME 6, NO. 6 and breeding experiments in a constant-temperature room, support the opinion of Racovitza that these animals lack an annual reproductive cycle. --G.W.M, GERSTENHAUER, ARMIN. International atlas of karst phenomena--Sheet 3, North Puerto Rico. Erdkunde, vol. 18, no. 2, suppl. 1, 3 sheets. June 1964. TYpical uplifted tropical Plio-Pleistocene karst occurs on Mid-Tertiary limestone of northern Puerto Rico. --G. W. M. GILEWSKA, SYLWIA. Fossil karst in Poland. Erdkunde, vol. 18, no. 2, p 124-135. June 1964. Four karst periods have existed in Poland since Permian time. Optimum conditions for karst development occurred in the mid-Tertiary during the early part of the present karst period when the climate was humid-tropical or sub'tropical. --G. W. M. GWOZDECKIJ, N. A. Bedeckter Karst in der UdSSR. Erdkunde, vol. IS, no, 2, p. 123-124. June 1964. The term "covered karst" should be restricted to karst covered by marine, glacial or river deposits, and distinguished from that covered only by limestone residuum. --G.W.M. HAYNES, C. VANCE, Jr. Science, vol. 145, no. Fluted projectile points: their age 3639, p. 1408-1413. Sept. 25, 1964. and dispersion. Clovis points are restricted to sediments between 11,000 and 11,500 years of age, such as those at Ventana Cave, Arizona, on the basis of radiocarbon dates. In the U. S., the points appear sharply in time, indicating a possible development elsewhere, such as in northern Alaska or the MacKenzie Valley. Further origin interpretation and study of man-mammoth relationships should be sought in this area. The author appears to accept fUlly the Two Creeks interpretation of Pleistocene chronology. --R.D. HSIANG-K llEI, YEH. A new Quaternary Testudo from Gigantopithecus Cave, Liucheng, Kwangsi. Vertebrata Palasiatica, vol. 7, no. 3, p. 223-226. 1963. A genus of tortoise, first appearing only in the Quaternary from this cave. scribed in this paper. in China in the A new species, Upper Eocene, is known Testudo tungia is de--R.D. LARSON, L. T. Geology and mineralogy of certain manganese oxide deposits. Economic Geology, vol. 59, p. 54-78. 1964. An account of the manganese oxide minerals in the Philipsburg district, Montana. The ores are secondary in origin, forming from oxidation of rhodochrosite, controlled by lithology, depth, solution passageways, and the watertable. Solution passageways in dolomite are a major factor in the True Fissure Mine. --A.L.L. MONROE, W. H. The eenjcn, a solution feature of karst topography in Puerto Rico. !!:. S. Geological Survey, Prof. Paper 501-8, p. 8-126-8129. 1964. Zanjones are joint-controlled trenches about 2 meters wide, 3 meters deep, and 50 meters long that form in thin-bedded limestone. They contrast with cutters, which form under soil cover, and with Lap fe s which form in massive limestone. --G.W.M, MURPHY, T, land and Some unusual low Bouguer anomalies of small extent in central Iretheir connection with geological structure. Geophysical Prospecting, 47


CAVE NOTES vol. 10, no. 3, p. 258-270. September 1962. A series of intense negative Bouguer anomalies, as large as -6.4 mgal. and up to one square kilometer in area are found over Carboniferous limestone. The cause of each anomaly must have a negative density contrast of 0.3 to 0.5 g/cm: with its top within 500 meters of the surface. The cause is concluded to be a sequence of solution cavities in the limestone, at present unknown. --A.L.L. ROGLIC, J. 113-116. "Karst valleys" in the Dinaric karst. June 1964. Erdkunde, vol. 18, no. 2, p. The term "karst valley" is a misnomer because typical ones were formed by superimposed rivers and therefore are not strictly karst features. --G. W. M. SMYK, BOLESLAW, and MARIA DRZAL. organismen auf das Ph~nomen der 102-113. June 1964. Untersuchungen Karstbildung. liber den Einfluss Erdkunde, vol. 18, von Mikrono. 2, p. Bacteria of the genus Arthrobacter limestone in central Europe. have been shown to decompose outcropping --G.W.M. SWEETING, M. M. Some factors in the absolute denudation of limestone terrains. Erdkunde, vol. 18, no. 2, p. 92-95. June 1964. Corbel's opinion that limestone solution is most rapid in cold climates is not supported by the facts. Production of CO a in the soil is more important than temperature in determining the rate of limestone solution. --G. W. M. SZAB6, P. Z. Neue ungen in Ungarn. Daten und Beobachtungen zur Kenntnis der Pal~okarsterscheinErdkunde., vol. 18, no. 2, p 135-142. June 1964. Fossil karst of Cretaceous age in Hungary contains bauxite deposits by the desilicification of clay in fossil dolinas. formed --G.W.M. WARWICK, GORDON T. vol. 18, no. 2, p. Dry valleys of the southern Pennines, 116-123. June 1964. England. Erdkunde, These dry valleys were formed by table caused the tributary valleys tributaries have now become hanging superimposed streams. Lowering of the water to dry up before the main streams, and the valleys. --G.W.M. WELLS, PHILIP V., and CLIVE D. JORGENSEN. Pleistocene wood rat middens and climatic change in Mojave Desert: A record of juniper woodlands. Science, vol. 143, no. 3611, p. 1171-1174. March 13, 1964. Radiocarbon dating of woodrat middens were obtained from shallow caves and rockshelters in the Paleozoic limestones and dolomites near Frenchman's Flat, Nevada. Dates range frOm 7800 to 40,000+ years. Neotoma lepida and Marmota flaviventris are identified as are numerous botanical fossi~e evidence is indicative of conditions of higher moisture, but still more arid than the typical pinyon-juniper environment. No discussion of the dating technique with respect to possible contamination from nearby nuclear testing is given. --R.D. ~TL, J. Fossile Grossformen im ostalpinen Karst. Erdkunde, vol. is, no. 2, p. 142-146. June 1964. Polje-like valleys in the eastern Alps were formed of underground drainage. during an earlier period Note to librarians: The index to CAVE NOTES. will be mailed with an early issue of Volume 7. Volumes 4 --G. W. M. through 6, Contributors: R.D.: R. deSaussure; A.L.L.: A. Lange; G.W.M.: George W. Moore, 48

Content: Cave detection by geoelectrical methods, part I:
resistivity / J. G. Day --
Proceedings --
Annotated Bibliography.
Cave Notes(vols. 1-8) and
Caves and Karst: Research in Speleology(vols. 9-15)
were published by Cave Research Associates from 1959-1973. In
1975, the Tumbling Creek Cave Foundation compiled complete
sets of the journals in three volumes. The Foundation sells
hardbound copies of the material to support its


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