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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General Note:
Content: Cave detection by geoelectrical methods, part II: transient and inductive methods / J. G. Day -- Review -- 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
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Vol. 7, no. 3 (1965)
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'Iile 7 CAVE NOTES A Review of Cave and Karst Research Volume 7. Number 3 May/June. 1965 CAVE DETECTION BY GEOELECTRICAL METHODS, PART II: TRANSIENT AND INDUCTIVE METHODS' by J. G. Day Galvanic: One extension of the basic method of resistivity determination is the measurement of time-dependent effects of the sudden application or removal of voltage between grounded electrodes. This method and its variations are known as Eltran (ELectrical TRANsient) techniques. When voltage is applied initially 'between two grounded electrodes, the steady-state value of current flow is not reached Immedtate ly, because of the electrical reactance of the ground. The inductive reactance of the longer, 'i e deeper, ground paths is greater than that of the more direct. shallow paths. This causes the current to flow near the surface at first and then to penetrate gradually to greater depths. The time constant'' of the ground circuit is approximately proportional to the square of the distance between the electrodes and inversely proportional to the resistivity of the ground. This time constant is also affected, to some extent, by the dielectric and electrolytic properties of the ground media. The Wenner electrode configuration, illustrated in Figure 3 of Part 1_ of this ee rtes", is seldom used in Eltran surveys, because of the undesirable inductive coupling which would exist between the current and potential circuits. To reduce such coupling, the potential electrodes are often placed outside of, and in line with. the current circuit (West, 1938). Another useful Eltran electrode arrangement is the right-angle configuration shown in Figure 1. This arrangement has the advantage of eliminating the effect of mutual inductance between the current and potential circuits almost entirely (Wait and Conda 1958). In Eltran surveys, the current circuit is supplied with a series of rectangular pulses from a source of constant voltage rather than constant current. One of the earliest means of measuring electrical tz-amii.ents was the use of a cathode-ray oscillograph synchronized with the application of power to the current circuit (Klipsch, 1939). This basic oscillographic technique can be augmented by the use of neutralization and/or compensation to CURRENT ELECTRODES 0-D --0, D '0 1 I o POTENTIAL I ELECTRODES b Figure L Right-angle array. lPart I of this series (Resistivity) appeared in Cave Notes, vol. 6, no. 6, 1964. 2The time required for the flow of current to reach 63.2~ (1 e1 ) of its steady-state value after the application of a constant voltage. 17


CAVE NOTES CAVE NOTES CAVE NOTES is a publication of Cave Research Associates. 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 Valley, Calif. Editor: Arthur L. Lange, Cave Research Associates Associate Editor: Ronald A. Brandon, Department of Zoology, Southern Illinois University, Carbondale, Illinois Managing Editor: R. deseuseure Cave Research Associates. @ Copyright 1965, Cave Research Associates. meaaure the amplitude and time constant of transient pulses (Saibara et a!., 1939). In one such method, the Sawtran technique, the signal from the potential circuit is applied to a variable -resistance-capacitance network which is then adjusted manually to produce a linear sawtooth wavefor-m on the oscillograph. _The time constant of the transient can be determined from the RC value of the network. As with the resistivity survey methods discussed in Part 1, Eltran data are interpreted by comparison with master curves established from standard earth models (Karcher and McDermott, 1935). The curves to be used depend on the earth model assumed from known local geological conditions and an the type of electr-ode arrangement employed. Somewhat similar to Eltran is the "ove rvo" method. This method, however, is based primarily on the measurement of induced polarization effects rather than inductive reactance. In practice, the earth is energized with a constant voltage for a few seconds and then the flow of current is cut off abruptly and the subsequent decay in voltage between two potential e Iectrodes is measured. The decay time constant may be measured in terms of milliseconds or seconds, depending on the electrical properties of the subsurface media. Various mechanisms have been propo ee d to account for induced polarization effects. Among these are: 1) electrolytic polarization of disseminated particles, 2) kinetic polarization accompanying electro-osmosis in porous rocks, and 3) ionic polarization across semipermeable membranes. The decay time constant for an overvoltage transient depends not only on the polarizability (i. e., the ability to receive a static charge of electricity) of the medium but also on its resistivity; and the product of resistivity and 'polarizability is roughly constant for a given type of rock, soil, or sediment (Keller, 1959). Limestones are among those rocks least sub-Ject to induced polarization, but cave sediments composed of clay and sand may have much greater polarizability. A cave containing such sediments might be detectable as a region of higher induced polarization than the surrounding limestone. In making overvoltage surveys, it is desirable to measure the integral of voltage (i.e., decay voltage) with respect to time, as this provides a parameter which is relatively independent of the effects of resistivity variations. For this purpose, oscillographic techniques or an integrating voltmeter can be used. 18


VOLUME 7, NO. 3 Inductive: It is possible to obtain useful resistivity data through the use of electromagnetic sensors rather than by means of potential electrodes. Also, in areas where it is difficult to make good electrical contact between current electrodes and the ground, as may be the case with dry sand or dry rock, it is often advantageous to -enexgiee the ground by inductive means. When inductive coupling is used, the choice of an appropriate operating frequency becomes of even greater importance than when galvanic contact electrodes are used (Haycock et al., 1949). 1£ the frequency is too low, the transfer of energy to and from the ground is not efficient. If the frequency is too high, the effective penetration may be too slight to reach the desired depth (Silverman and Sheffet, 1942). Also, the higher frequencies are more subject to terrain effects and elliptical polarization due to subsurface phase shifts. The amount of electrical power required for inductive methods depends, in part, on the frequency used, the depth of penetration desired, the size and type of radiating element used, and the sensitivity of the sensing equipment. One of the simplest 'portable signal generators consists of a batteryoperated buzzer in series "With the primary winding of an output transformer. Such a signal generator can supply 10 or 20 watts of power at frequencies in the neighborhood of 10'00 cps. Thil::l should be adequate power for most speleological surveys in areas where soil conductivity is not too great. A transistorized signal generator having an adjustable output frequency can provide better signal stability and somewhat higher power efficiency (Bitterlich J 1962). Motor-generator units can also be used as signal generators. Inductive coupling from a signal generator to the ground is usually accomplished by means of a large horizontal loop antenna. The antenna can be either circular,' square, or rectangular in shape. A vertical loop antenna can also be used, although the relatively low power efficiency of a vertical antenna is a serious disadvantage. However, this disadvantage is somewhat offset by the ability of a vertical radiator to penetrate conductive near-surface layers. Therefore, a vertical loop antenna could prove useful in the detection of vertical caves beneath a conductive overburden. A small reception coil is the most common type of irtductive sensor. The received signal is amplified and then applied to an electronic voltmeter which provides an indication of field intensity. The reception coil is often mounted on a rotatable frame, so that it can be shifted about a horizontal and vertical axis to enable the orientation of the plane of polarization to be determined. Reception coils are usually about 30 ern, in diameter and consist of a few hundred turns wound on an air core. Although many variations and refinements of inductive methods have been developed, most of them involve the measurement of in-phase and quadrature (i.e., 90¡ out of phase) fields produced by components of the primary field and secondary fields induced in the earth. Anorrra.Ioua field configurations are indicative .of a foreign body. or. possibly, a void. Detailed descriptions of such methods are to be found in the literature (Heiland, 1946; Dobrin, 1960; and Jakosky, 1961). One electromagnetic technique which differs significantly from the others is the "capactty" method of Volker Fritsch (1943). This method is based on the fact that the resonant frequency of an antenna is affected by the presence of conductive media in the vicinity. In practice, a long horizontal antenna is po ai.ticne d at a known height above the surface of the ground. This an-, tenna is a frequency-controlling element in an oscillator circuit. The resonant frequency of the oscillator circuit is compared with that of a standard oscillator, by means of heterodyning. To obtain depth resolution, measurements are made at various antenna heights. Fritsch has successfully located caves by this method, although it has not been found reliable in all cases. 19


CAVE NOTES Telluric: In areas where soil resistivity is very low, it is difficult to achieve useful depths of penetration by either galvanic or inductive coupling. The near-surface layer tends to mask the effects of deeper strata. Fortunately, it is possible to overcome this difficulty, at least to some extent, by making use of natural earth currents which exist not only at the surface but also at great depths (Fleming, 1949). These telluric currents circulate in great sheets. or whorls, thousands of miles across. Although the exact mechanism by which they arise is not certain, the primary cause seems to be an inte rac tdon between the' earth's magnetic field and the flow of charged particles from the sun (Hopkins, 1960). The four principal whorls of telluric currents form a pattern which somewhat resembles a gigantic fou r-deaf clover, with the center of the pattern fixed on an imaginary line between the center of the earth and the sun. This patte'rn retains its basic shape and orientation as the earth revolves I causing diurnal va'rdatfous in telluric current fl.ow at any given location on. or in. the earth. There are also diurnal distortions in the pattern which are caused by Iaege e s c ake resistivity differences, as between continents and oceans. Hodograms of the telluric field vector, measured over a 24~hour period at any given location. take the form of a rouglily elliptical envelope. Such an envelope, with the origin at the center, is ofiten so elongated as to be almost a line. The principal direction of a telluric field vector hodogram is influenced by local topography and subsurface resistivity conditions (Wescott and Hessler, 1960).. When telluric currents encounter a region of high subsurface resistivity. such as a cave.' the telluric field increases at the surface above that region, as the currents avoid flowing through resistive media (Douglass, 1962). Although it ts not practical to attempt to measure the earth currents themselves. measurements can be made of telluric surface potentials by means of non-polariza:ble electrodes. Such an electrode consists of a metal rod immersed i~ a solution of its own aalt, Disadvantages inherent in this technique arise from the presence of contact potentials and thermoelectric potentials which, particularly for short irite r -e'le ct r-ode spacings. may be many times greater than the telluric surface potential between the el.ect.rode s., It is possible to counrea-act these unwanted potentials I but care must be exercised to avoid erroneous measurements. as telluric potentials seldom exceed one millivolt per meter of inter-electrode spacing and frequently are less than 0.1 millivolt per rnete r ~: The signals or potentials measured in any type of geoelectrical survey are generally quite small and may easily be obscured by stray currents and noise from any of a number of possible sources (Vinogradov, 1961). Errors can result from fluctuating contact potentials at electrodes, incidental inductive or capacitive coupling, unintentional grounding of equipment, and excessive loading of sensors by instrumentation cicuits. While power lines and electrical equipment are undoubtedly responsible for most of the electromagnetic noise in urban areas, a considerable amount of low-frequency noise is often observed in areas far removed from such sources. Much of this noise is the result of lightning discharges, not only in the immediate vicinity but also at great distances (Schonland, 1956). There is Ie e s atmospheric noise at about 3.5 kc than at any other frequency below 10 kc (Maxwell and Stone, 1962). Also. noise propagated through the atmoephe r-e is 'predomina~tly vertically polarized, making the use of horizontally polarized inductive sensors advantageous. 20


VOLUME 7, NO .3 Choosing a survey method: The choice of an appropriate geoelectrical survey method to sutt a given set of conditions can be a difficult one. In many cases, it may be worthwhile to determine the local resistivity profile by means of galvanic resistivity measurements. If the Boil resistivity is unusually high, then inductive methods may be appropr-iate ; On the other hand, if the soil resistivity is low, telluric methods may yield better results. If none of these techniques provide conclusive evidence. Eltran or overvoltage methods may prove useful. As is the case with any geophysical survey technique, the data obtained in electrical surveys must be carefully interpreted with respect to the effects of the local topography and probable subsurface conditions. It may also be worthwhile to compare apparent resistivities measured at the same station of a survey but at different azimuthal orientations, to detect any resistivity anisotropies which may exist in the subsurface media (Piz eon, 1935). It might be possible, in some instances, to detect even water-filled' caves by observing anomalies in subsurface anisotropy. Although there is, as yet, little quantitative information available by which to compare the relative efficacy of electrical cave detection methods and other geophysical methods, it appears likely that eke ctr-ic al. methods can be of value in areas where other techniques may be inconclusive. References: BITTERLICH, W. On the propagation of VLF waves in solids. ~ Annua.l Tech~ Report. Innsbruck, Austria. 66p. 1962. DOBRIN, M. B. Introduction to Geophysical Prospecting. McGraw Hill Book cc., New York. 446p. 1960. DOUGLASS, J. L, Upper Crustal Inhomogeneities and their Effect on Telluric Currents. Californii:lUni v., Dept of Mineral Te'Chiiology, M. S. thesis, B'erkeley. 'i962:"" FLEMING, J. A. Terrestrial Magnetism and Electrici ty. Dover Publications, New York. 1949. FRITSCH, V. Messverfahren der Funkmutung, Oldenbourg, Munich and Berlin. 220p. 1943. HAYCOCK, O. C., E. C. MADSEN, and S. R. HURST. Propagation of electromagnetic waves in earth. Geophysics, vol. 14, p 162-171. 1949. HEILAND, G< A. Geophysical Exploration. Prentice-Hall, New York. 1013p. 1946. HOPKINS, G. H., Jr. A survey of past and present investigations of the natural earth currents. Texas Univ., Electrical Engineering Laboratory Rept no. 113, 32p. 1960. JAKOSKY, J. J. Exploration Geophysics. Trija Publ. Co., Newport Beach, Calif. 1195p. 1961. KARCHER, J. and E. McDERl\I)TT. Deep electrical prospecting. Amer Assoc. of Petroleum Geologists Bull., vo L. 19, p. 65-77. 1935. ---KELLER, G. V. Analysis of some electrical transient measurements on igneous, sedimentary, and metamorphic rocks. (in WAIT, J. R. -Ed. Overvoltage Research and Geophysical Applications. PergammonPress, New York. 1959) p 92-11l. KLIPSCH, P. W. Recent developments in Eitron prospecting. Geophysics, vol. 4, p. 283-291. .1939. MAXWELL, E. L., and D. L. SroNE. Natural ~ Electronics, Lnc., Rept no. 30-P-3. noise fields from 1 cis to 100 kc, 26p. Boston, Mass. 1962. 21


CAVE NOTES PIRSON, S. J. Effect of anisotropy on apparent resistivity curves. Amer. Assoc. of Petroleum Geologists BUll., vo L. 19, p. 37. 1935. ---SAIBARA, R., S. BILINSKY, and W. McLARRY. Exploration by incremented wave distortion. United ~ Patent 2,177,346; issued October 24, 1939. SCHON1JtND, B. The lightning discharge. (in HANDBUCH ~ PHYSIK, Springer Vlg. Berlin. 1956) vol. 22, p. 576. SILVERMAN, D. and D. SHEFFET, Note on the transmission of radio waves through the earth. Geophysics, vol. 7, p 406-413. 1942. VINOGRADOV, P. A. The radius of influence of stray cur-nent e on recordings of electrotelluric field variations. Geologiya! Geofizika, no. 2, p. 121-124, 1961. WAIT, J. R. and A. M. CONDA. On the measurement of ground conductivity at VLF. Ins t of ~ Engineers, Transactions on Antennas and Propagation, vol. AP-6. p. 273-277. 1958. WESCOTT, E. M. and V. P. HESSLER. The effect of topography and geology on telluric currents. Alaska Univ., Geophysical Lns t. Scientific Rept no. 3, 30p. 1960. WEST, S. S. Electrical prospecting with non-sinusoidal alternating currents. Geophysics, voL 3, p 306-314. 1938. REVIEW SCHNITZER, WALTER A. Die Markierung unterirdischer Wasserwege mit Hille von Alkylbenzolsulfonaten (Detergentien). Ge.2l2gische ~tter fur Nordost-Bayern. Band IS, Heft I, S. 50-56. 1965. Early attempts to trace the course of underground streams were made with straw chaff and various dyes. The difficulties encountered were dilution below detectable levels, filtration, oxidation, adsorption. and excessive cost. Combinations of methods, such as NaCl (AgNQ3 detector) plus fluorescein are probably best, though lycopodium spore techniques have shown prOIntee in recent trials. Comme i-ctal. detexgenta and some ordinary washing powders may be detected by their foam, formed at dilutions on rne order of 1/1,000.000. as may be noted in the disastrous contamination of many lakes am! streams. Detergents have recently been developed that are as rrruch as 90 % degradable through bacterial action. Those which contain additional foam stabilizers might be suitable as water tracers, according to Schnitzer, Three trials are described briefly. In one case, 0.75 kg of detergent was added to flowing water, and in two other tests, 3 kg were flushed into dry dolines along with several hundred liters of water. The foam ~sfirst detected 70 minutes to 4 hours after commitment, at known springs and. in one case, at a spring in a river bed 2.5 km distant. A subsequent article by the author will treat the influence of hard water, temperature change, and prolonged delays. No mention was made of the possible immediate effect that detergents might have on stream and cave life, even though the detergent is of a type which will ultimately decompose. In my opinion. it would be particularly dangerous to use detergents without foam stabilization and to assume that the absence of suds on a e trearn or in a test shaker is an indication of the absence of chemical effect on living organisms. Further tests are required in order to demonstrate the non-toxicity of these substances. Neely H. Bostick, Cave Research Associates 22


VOLUME 7, NO. 3 ANNOTATED BIBLIOGRAPHY Contributors are requested to include the addresses of authors where convenient, so that reprints may be requested for the library. EULER, R. C., and A. P. OLSON. Split-twig figurines from northern Arizona: new radiocarbon dates. ~, voL 148, p. 368-369. April 16, 1965. Recently released radiocarbon cates for split-tWig figurines from Marble Canyon, Arizona, are 4095 . 100 years ago; they substantiate previously determined dates of 3530 300 and 3100 . llO.years ago. A recently excavated site in Walnut Canyon, Arizona, extends the geographical range of the figurines. The dates of samples from this site are 3500 . 100 and 3880 . 90 years ago. It is hypothesized that the figurines were magicorel1gious artifacts related to the Pinto complex of the Desert CUlture. --Authors H. A. rSClR"eJjl(l,il. KPynHEAlllHE KAPCTOBblE nEWEPbl MHPA M CCCP. GVOZDETSKY, N. A. The very largest caves in the world and in ~he U.S.S.R. All~ Geographical Society, ~, vol. 96, p. 239-241. 1964 (in Russian). Recent Western cave literature on the extent of large caves is summarized, and though found to be inaccurate, the author concludes that their distances exceed the newly-measured distances within large Sbviet caves. Crystal Cave in the USSR has 18.7 kID of passage length. Measurements of Soviet caves are listed along with dimensions of the world's largest caves for comparison by the Russian-reading audience. --H. T. KAMB, BARCLAY, and E. LaCHAPELLE. Direct observation of the mechanism of glacier sliding over bedrock. Jnl of Glaciology, vol. 5, p 159-172. 1964. Studies were conducted at the head of a tunnel reaching bedrock in the Blue Glacier, Washington. In addi 't t on to the general physical effects measured, the generation of caverns by ice flowing over bedrock obstacles, and the formation of regelation spicules were studied. Field measurements and laboratory work were combined in this program. --A. L. L. LANNING, E. C. The Musira burial caves. ~, vo L. 64, Art. 137, p.1l6-II7, 1964. Human burials are described from caves on Musira Island in Lake Victoria, Africa. No burial goods were found during the brief visit by the author. A clay fumigator was recovered from one cave by a previous party. --L.A. P. LOWRY, D. C. Pa Lygor-akf te in a cave in New Zealand. New ~ Jal of Geology and Geophys Lcs vol. 7, p 917. 1964. Palygorskite in Broken Hill Cave and other caves occurs in veins in the wall rock, but is believed to be younger than the caves. --G.W.M. PARKER, G. G., L. M. SHOWN, and K. W. RATZLAFF. Officer's Cave, a pseudokarst feature inaltered tuff and volcanic ash of the John Day formation in eastern Oregon. Geological Society of America, Bull., vol. 75, p. 393-402. May 1964. Officer's Cave and nearby karstlike topography are developed in tuff and volcanic ash, which are relatively insoluble. These result from erosion proceeding underground through cracks, joints, and along the cave r Ioor The cave enlarges at an average rate of 2700 cubic feet per year, through spallation, sheeting, and particle removal of the caye floor. --A.L.L. POULSON, THOMAS L. cave adaptation in amblyopsid fishes. American Midlano Na- turalist, vol. 170, no. 2, p 257-290. October 1963. A detailed study of the sequential adaptation of the amblyopsid logaster, 'l)rphlichthys, and Amblyopsis to the cave environment. fishes Cho--R.A.B. 23


CAVE NOTES RANDALL, A. G. Geologic da ting of selected archaeological si tes in the Rocky Mountain region. Rocky Mountain Geologist, vol. 2, no. 1, p. 35-41. 1965. Changes in tools of ear-Ly man help to provide a stratigraphic record, distinguishing between early, middle, and late Recent deposits and Pleistocene sediments. Of 43 selected sites studied, 13 were found of late Pleistocene age. Caves and surface s t tes are catalogued, --A. L. L. SMI'IH, G. A. Split-twig figurines from San Bernardino County, California, Mast.e r-key vol. 37, no. 3, p. 86-90, July-September 1963. Fi ve complete and many fragments of split-twig figurines were found in Newberry Cave in the Mojave Desert. These specimens represent the only known tWig figurines in California. Discus~ion of the Grand Canyon examples in relation to the California collection is given, --L.A. P. 6. M. eMOA,"UK". onur nPHMEHEHH nOl\3EMHOW 31lEKTPOPA3BEI\KH HCCIlEI\OBAHHH KAPCTA. SMOLI NIKOV, B, M. Attempt to use underground electrical vestigations. Akad Nauk Uk ru Ln. ~, ~, Geofiziki, (7), p 71-74, 1963, Preliminary results of resistivity sounding and profiling Cavern in the Crimea demonstrate the value of such surveys karst. nPH surveying in karst inaeor t e. ~, no. 5 in the Kyzyl-Koba in the study of --A. L, L, A, L, L . A. Lange; 24

Content: Cave detection by geoelectrical methods, part II:
transient and inductive methods / J. G. Day --
Review --
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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