Water tracing experiments were successfully conducted over a distance of ten kilometers along the base of Variegated Glacier for the purpose of characterizing the water drainage system of the glacier in the surging as compared to the non-surging state. Three tracing experiments were conducted, and fluorescent dyes, Rhodamine WT and Tinopal AMS, were injected into boreholes at separate locations. The two Rhodamine WT experiments were conducted over a 10 km distance, both during the most rapid surging motion of the glacier, and after its cessation.
\r\n\r\nIn each experiment, the terminus streams were monitored for stream discharge, sediment content and tracer concentration. Rhodamine WT tracer was significantly adsorbed on the suspended sediment, particularly during the surge. The adsorption behavior followed the Langmuir model, and calculated distribution coefficients of Kd = 100 to 1000 ml/g were measured for during the glacier surge. The Kd values measured after the surge were lower than during the surge by a factor of 10 to 1000. The much higher Kd values in the surging as compared to non-surging glacier states can be best explained by a factor of 10 to 1000 decrease in the modal and/or mean grain-size of the suspended sediment. The abundance of fine-grained sediment during the surge is probably due to increased grinding of rock material at the glacier bed.
\r\n\r\nTheoretical models of tracer dispersion in a single tunnel, were compared to models of dispersion in linked-cavity systems to infer the details of water flow at the glacier bed. The broad, roughly symmetrical, dye-return curve measured during the glacier surge conforms to diffusive dispersion theory, and differs sharply from the highly asymmetrical dispersion curve measured after the surge. Results indicate the dispersion behavior, and calculated Manning roughness, of the post-surge Variegated Glacier is similar to those of glaciers that do not surge. The drainage system of the Variegated Glacier in the surging state is consistent with a model of tracer dispersion in an interconnecting network of conduits and cavities, and is strikingly different from the tunnel system indicated for the non-surging state.
\r\n", "doi": "10.7907/VSHG-G674", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:2695", "collection": "thesis", "collection_id": "2695", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06232004-134838", "primary_object_url": { "basename": "Kieffer_sw_1971.pdf", "content": "final", "filesize": 10847673, "license": "other", "mime_type": "application/pdf", "url": "/2695/1/Kieffer_sw_1971.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "I. Shock Metamorphism of the Coconino Sandstone at Meteor Crater, Arizona. II. The Specific Heat of Solids of Geophysical Interest", "author": [ { "family_name": "Kieffer", "given_name": "Susan Werner", "clpid": "Kieffer-Susan-Werner" } ], "thesis_advisor": [ { "family_name": "Shoemaker", "given_name": "Eugene Merle", "clpid": "Shoemaker-E-M" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPART I: A study of the shocked Coconino sandstone from Meteor Crater, Arizona, was undertaken to examine the role of porosity in the compression of rocks and in the formation of high-pressure phases. A suite of shocked Coconino specimens collected at the crater is divided into five classes, arranged in order of decreasing quartz content. The amounts of coesite, stishovite (measured by quantitative x-ray diffraction) and glass vary systematically with decreasing quartz content. Coesite may comprise one-third by weight of some rocks, whereas the stishovite content does not exceed 1%. The five classes of rocks have distinct petrographic properties, correlated with the presence of regions containing coesite, stishovite or fused silica. Very few occurrences of diaplectic glass are observed, in striking contrast to its abundant occurrence in the non-porous rocks from the Ries Crater.\r\n\r\nIn the lowest stages of shock metamorphism (Class I), the quartz grains are fractured and the voids in the rock are filled with myriads of small chips derived from neighboring grains. The fracture patterns in the individual quartz grains are controlled by the details of the initial morphology of the colliding grains. In one weakly shocked rock, it was possible to map the general direction of shock passage by recording the apparent direction of collision of individual grains. The principal mechanism of energy deposition by a shock wave in a porous material is the reverberation of shock and rarefaction waves through grains due to collisions with other grains. A one-dimensional model of the impact process can predict the average pressure, volume and temperature of the rock if no phase changes occur, but cannot predict the observed nonuniformity of energy deposition.\r\n\r\nIn all rocks shocked to higher pressure than was necessary to close the voids, high-pressure and/or high-temperature phases are present. Locally high pressures enduring for microseconds and high temperatures enduring for milliseconds controlled the phases of SiO2 which formed in the rock. Collapsing pore walls became local hot spots into which initial deposition of energy was focused. Microcrystalline coesite in Class II rocks occurs in symplektic regions on quartz grain boundaries which were regions of initial stress and energy concentration, or in sheared zones within the grains. The occurrence and morphology of the coesite-rich regions can be explained only if the transformation from quartz to coesite proceeds slowly in the shock wave. In Class III rocks, microcrystalline coesite occurs in opaque regions which surround nearly isotropic cores of cryptocrystalline coesite. The cores are interpreted to be the products of the inversion of stishovite (or a glass with Si in six-fold coordination) which initially formed in the shock front in regions of grains shocked to pressures near 300 kb. Stishovite is preserved only in the opaque regions, which are believed to have been cooler than the cores.\r\n\r\nIn Class IV rocks, vesicular glass occurs in core regions surrounded by opaque regions containing coesite. The relation of the glass to the coesite and quartz suggests that the glass was formed by inversion of stishovite formed above 350 kb upon release to lower pressure.\r\n\r\nClass V rocks are composed almost entirely of glass with vesicles uniformly distributed in the glass. These vesicles were probably formed by exsolution of water that had been dissolved in melted SiO2 during passage of the shock.\r\n\r\nPART II: The use of Debye temperatures as parameters for material properties of silicate minerals is becoming common in geophysical studies. The elastic Debye temperature, [...] alone is, in general, insufficient to specify properties which depend on lattice vibrations. Two effects ignored by the Debye model are shown to be important: high frequency lattice vibrations and the dispersion relation. As an alternative to the Debye model, a somewhat more complicated model is proposed that is still reasonably convenient and is able to account much better than the Debye model does for the variation of specific heat of complex substances over a wide range of temperature. This model is designated the acoustic-optic model. The parameters required for this model are the maximum lattice vibrational frequency, the elastic Debye temperature, and the specific heat at a single (say, room) temperature. Adequate approximations to these parameters are generally available.\r\n\r\nTo consider heat capacity data and compare the data with either the Debye or acoustic-optic model, the calorimetric Debye temperature, [...] is considered. [...] is the value of Debye temperature that will reproduce the specific heat at constant volume at the temperature T. For silicates, a large increase at high temperatures in [...] above the elastic Debye temperature is due to the presence of oscillators between the elastic Debye frequency and a maximum vibrational frequency which exceeds the Debye frequency. Vibrations of these oscillators cause the spectral lines observed at infrared frequencies. The proposed model takes these oscillators into account by adding a constant valued continuum to an assumed low-frequency Debye spectrum.\r\n\r\nIn all substances considered, [...] at low temperatures initially decreases to values below [...]. This decrease is believed due to the dispersion relation, i.e., the nonlinear relation between the wave vector and the frequency.\r\n\r\nIn two substances of geophysical interest, NaCl and MgO, the maximum observed vibrational frequency is depressed below the observed elastic Debye frequency as a consequence of the dispersion relation. The acoustic-optic model is capable of predicting the specific heat of these two substances and the acoustic-optic spectra which result from application of the model to these substances describe qualitatively the spectra that result from the dispersion relation.\r\n\r\nThe nonlinearity of the dispersion relation dominates the specific heat behavior of NaCl and MgO and influences the low temperature behavior of all silicates with varying degrees of severity. The effect of the dispersion relation can be ignored for some silicates if specific heats only at high temperatures (T > 100[degrees]K) are considered. The effect cannot be ignored in the case of rutile or stishovite.", "doi": "10.7907/XBPD-6Y42", "publication_date": "1971", "thesis_type": "phd", "thesis_year": "1971" }, { "id": "thesis:2919", "collection": "thesis", "collection_id": "2919", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07182006-094012", "primary_object_url": { "basename": "Raymond_cf_1969.pdf", "content": "final", "filesize": 11263450, "license": "other", "mime_type": "application/pdf", "url": "/2919/1/Raymond_cf_1969.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Flow in a Transverse Section of Athabasca Glacier, Alberta, Canada", "author": [ { "family_name": "Raymond", "given_name": "Charles Forest", "clpid": "Raymond-Charles-Forest" } ], "thesis_advisor": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Measurements of ice deformation at the surface and at depth in the Athabasca Glacier, Canada, reveal for the first time the pattern of flow in a nearly complete cross section of a valley glacier, and make it possible to test the applicability of experimental and theoretical concepts in the analysis of glacier flow. Tilting in nine boreholes (depth about 300 m, eight holes essentially to the bottom) was measured with a newly developed electrical inclinometer, which allows a great increase in the speed and accuracy with which borehole configurations can be determined, in comparison with earlier methods. The measurements define the distribution of the velocity vector and the strain-rate tensor over 70% of the area of the glacier cross section.\r\n\r\nThe main longitudinal component of flow has the following general features: (1) basal sliding velocity which exceeds 70% of the surface velocity over half of the width of the glacier, (2) marginal sliding velocity (not more than a few meters per year) much less than basal sliding velocity at the centerline (about 40 m yr(-1)), (3) marginal shear strain rate near the valley walls two to three times larger than the basal shear strain rate near the centerline (0.1 yr(-1)).\r\n\r\nThe observed longitudinal flow is significantly different from that expected from theoretical analysis of flow in cylindrical channels (Nye, 1965). The relative strength of marginal and basal shear strain rate is opposite to that expected from theory. In addition, the longitudinal flow velocity averaged over the glacier cross section (which determines the flux of ice transported) is larger by 11% than the average flow velocity seen at the glacier surface, whereas it would be 2% smaller if the theoretical prediction were correct. These differences are caused to a large extent by the constant sliding velocity assumed in the theoretical analysis, which contrasts strongly with the actual distribution of sliding. The observed relation between marginal and basal sliding velocity is probably a general flow feature in valley glaciers, and may be caused by lateral variation of water pressure at the ice-rock contact. The observed pattern of longitudinal velocity over the section also shows in detail certain additional features incompatible with the theoretical treatment, even after the difference in boundary conditions (distribution of sliding velocity) is taken into account.\r\n\r\nLongitudinal strain rate (a compression of about 0.02 yr(-1) at the surface) decreases with depth, becoming nearly 0 at the bed in the center of the glacier. The depth variation cannot be explained completely by overall bending of the ice mass as a result of a longitudinal gradient in the curvature of the bed, and is at variance with existing theories, which require the longitudinal strain rate to be constant with depth.\r\n\r\nMotion transverse to the longitudinal flow occurs in a roughly symmetric pattern of diverging marginward flow, with most of the lateral transport occurring at depth in a fashion reminiscent of extrusion flow. The observed lateral velocities averaged over depth (up to 1.9 m yr(-1)) are compatible with the lateral flux required to maintain equilibrium of the marginal portions of the glacier surface under ablation (3.7 m yr(-1)) and are driven by the convex transverse profile of the ice surface.\r\n\r\nWhen the measured strain-rate field is analyzed on the basis of the standard assumption that the shear stress parallel to the glacier surface varies linearly with depth, the rheological behavior in the lower one-half to two-thirds of the glacier is found compatible with a power-type flow law with n = 5.3. However, the upper one-third to one-half of the glacier constitutes an anomalous zone in which this treatment gives physically unreasonable rheological behavior. In a new method of analysis, rheological parameters are chosen so as to minimize the fictitious body forces that appear as residuals in the equilibirum equations when evaluated for the measured strain-rate field. This new method requires no a priori assumptions about the stress distribution, although for simplicity in application, the mean stress is assumed constant longitudinally. This treatment shows that the anomalies in the near-surface zone are due to significant departures from linear dependence of shear stress on depth, and gives a flow-law exponent of n = 3.6, which is closer than n = 5.3 to values determined by laboratory experiments on ice.", "doi": "10.7907/E6A2-B010", "publication_date": "1969", "thesis_type": "phd", "thesis_year": "1969" }, { "id": "thesis:2906", "collection": "thesis", "collection_id": "2906", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07172006-093716", "primary_object_url": { "basename": "Kiefer_hh_1968.pdf", "content": "final", "filesize": 7761340, "license": "other", "mime_type": "application/pdf", "url": "/2906/1/Kiefer_hh_1968.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Near Infrared Spectral Reflectance of Simulated Martian Frosts", "author": [ { "family_name": "Kieffer", "given_name": "Hugh Hartman", "clpid": "Kieffer-Hugh-Hartman" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In view of the apparent conflict between spectral observations and recent theories of the Martian polar caps, comparison spectra were obtained for frosts of relevant composition and grain size. The spectral reflectances of frosts formed from pure CO2, and pure H2O and mixtures of these gases have been measured from 0.8 to 3.2 [microns]. Low-weight fractions or small surface concentrations of H2O resulted in spectra similar to pure H2O frost spectra. The concentration of the condensable gas and the radiation balance effect the frost textural scale and the contrast of the reflection spectrum. The emissivity of the polar caps may be small, in contrast to previous assumptions. Probable processes of frost formation and sublimation on Mars and seasonal variations of frost composition suggest that reflection spectra obtained in the Martian spring may be misleading. In light of the laboratory results and probable Martian conditions, previous suggestions that the Martian polar caps are H2O are not valid. Future diagnostic observations in the near and thermal infrared are suggested.\r\n\r\nFigures 10, 11 and 12 are photographs of frost samples and will not reproduce well. Photographic copies may be ordered.\r\n", "doi": "10.7907/BHED-BJ17", "publication_date": "1968", "thesis_type": "phd", "thesis_year": "1968" }, { "id": "thesis:4078", "collection": "thesis", "collection_id": "4078", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10142002-113121", "primary_object_url": { "basename": "Blandford_rr_1964.pdf", "content": "final", "filesize": 7030464, "license": "other", "mime_type": "application/pdf", "url": "/4078/1/Blandford_rr_1964.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Stratified Inertial Flow in the Gulf Stream", "author": [ { "family_name": "Blandford", "given_name": "Robert Roy", "clpid": "Blandford-Robert-Roy" } ], "thesis_advisor": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Earlier theoretical models of the Gulf Stream have treated the motion of a single fluid layer of constant density and vertically uniform flow velocity. As a step toward models with continuous stratification, the present work analyses inviscid, steady-state, purely inertial flow using two moving layers of different density and velocity.
\r\n\r\nThe first type of Gulf Stream model analysed consists of two layers of different densities flowing over a denser layer at rest (baroclinic model). The second has two layers of different densities flowing over a rigid, horizontal bottom (mixed barotropic-baroclinic model).
\r\n\r\nIn both models there exist, at any latitude, either 0, 2, or 4 theoretical solutions to the flow problem. Only one such solution, however, is realistic and satisfies the boundary condition of vanishing northward velocity at the southern latitude boundary of the flow region considered. This is called the correct solution, while the others are called incorrect solutions. As the parameters of the two-layer models converge to limiting values corresponding to one-layer models (for example, vanishing density difference between the upper and lower layers), the solutions may or may not converge to the one-layer solutions. If a correct solution converges uniformly, the limit is called a correct limit. If convergence is non-uniform at some value of the latitude coordinate, the limit is called an incorrect limit. If no solutions exist as the limit is approached, it is an impossible limit.
\r\n\r\nThe most important limits discussed are as follows:
\r\n\r\n1. As the density contrast between the upper and lower moving layers becomes large in a baroclinic model for which the upper layer increases in thickness with latitude in the interior of the ocean to the east of the stream, the upper layer goes, via a correct limit, to the one-layer baroclinic model.
\r\n\r\n2. As the density contrast between the upper and lower layers becomes small in a baroclinic model, the solution for the sum of the two layers converges, via an incorrect limit, to the one-layer baroclinic model.
\r\n\r\n3. As the thickness of the upper layer becomes small while the density difference across it remains proportional to the thickness (a constant density \"gradient\" in the upper layer), the range of latitude over which there exists a correct solution tends to zero. The incorrect solution goes to the one-layer model via an incorrect limit. This result suggests that continuously stratified, purely inertial models of the Gulf Stream are impossible for finite density gradients.
\r\n\r\n4. In the limit as the interface between the lower moving layer and the resting layer becomes horizontal, the lower layer velocity goes to zero. No solution exists as the limit is approached. It is an impossible limit.
\r\n\r\n5. As the density contrast between the upper and lower layer becomes small in the barotropic-baroclinic model, the solution goes via a correct limit to the homogeneous barotropic model.
In an attempt to model the actual Gulf Stream, parameters are selected for a model of two moving layers, the upper about 600 meters thick and the lower about 400 meters. This model is close to the impossible limit of 4. above, and no solution exists. The physical reason for this is that because of the small transport in the lower layer, the velocity in the lower layer must be small, which is incompatible with the large velocity gradient needed for conservation of potential vorticity as required in an inertial model. It therefore seems questionable that the deeper waters of the Gulf Stream can be modelled by a purely inertial theory.
\r\n\r\nNo off-shore countercurrents can be found, despite fairly accurate modelling of boundary conditions which might be expected to give them.
\r\n\r\nThe general implication of this work is that steady, purely inertial models are inadequate to describe even the lower latitude growth region of Gulf Stream if density stratification is taken into account, and that viscosity or unsteadiness must therefore be introduced.
", "doi": "10.7907/JSQN-6Y34", "publication_date": "1964", "thesis_type": "phd", "thesis_year": "1964" }, { "id": "thesis:7714", "collection": "thesis", "collection_id": "7714", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05152013-140445759", "type": "thesis", "title": "Mathematical Study of Finite-Amplitude Rock-Folding", "author": [ { "family_name": "Chapple", "given_name": "William Massee", "clpid": "Chapple-William-Massee" } ], "thesis_advisor": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The problem of the finite-amplitude folding of an\r\nisolated, linearly viscous layer under compression and\r\nimbedded in a medium of lower viscosity is treated theoretically\r\nby using a variational method to derive finite difference\r\nequations which are solved on a digital computer. The\r\nproblem depends on a single physical parameter, the ratio\r\nof the fold wavelength, L, to the \"dominant wavelength\" of\r\nthe infinitesimal-amplitude treatment, L_d. Therefore, the\r\nnatural range of physical parameters is covered by the\r\ncomputation of three folds, with L/L_d = 0, 1, and 4.6, up\r\nto a maximum dip of 90\u00b0.
\r\n\r\nSignificant differences in fold shape are found\r\namong the three folds; folds with higher L/L_d have sharper\r\ncrests. Folds with L/L_d = 0 and L/L_d = 1 become fan folds\r\nat high amplitude. A description of the shape in terms of\r\na harmonic analysis of inclination as a function of arc\r\nlength shows this systematic variation with L/L_d and is\r\nrelatively insensitive to the initial shape of the layer.\r\nThis method of shape description is proposed as a convenient\r\nway of measuring the shape of natural folds.
\r\n\r\nThe infinitesimal-amplitude treatment does not\r\npredict fold-shape development satisfactorily beyond a\r\nlimb-dip of 5\u00b0. A proposed extension of the treatment\r\ncontinues the wavelength-selection mechanism of the\r\ninfinitesimal treatment up to a limb-dip of 15\u00b0; after\r\nthis stage the wavelength-selection mechanism no longer\r\noperates and fold shape is mainly determined by L/L_d and\r\nlimb-dip.
\r\n\r\nStrain-rates and finite strains in the medium are\r\ncalculated f or all stages of the L/L_d = 1 and L/L_d = 4.6\r\nfolds. At limb-dips greater than 45\u00b0 the planes of\r\nmaximum flattening and maximum flattening rat e show the\r\ncharacteristic orientation and fanning of axial-plane\r\ncleavage.
\r\n", "doi": "10.7907/FCVB-NS79", "publication_date": "1964", "thesis_type": "phd", "thesis_year": "1964" }, { "id": "thesis:6583", "collection": "thesis", "collection_id": "6583", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08152011-090459434", "primary_object_url": { "basename": "Conel_je_1962.pdf", "content": "final", "filesize": 65066413, "license": "other", "mime_type": "application/pdf", "url": "/6583/1/Conel_je_1962.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Studies on the Development of Fabrics in Some Naturally Deformed Limestones", "author": [ { "family_name": "Conel", "given_name": "James Ekstedt", "clpid": "Conel-James-Ekstedt" } ], "thesis_advisor": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The purpose of this investigation has been to study in detail the development of deformation fabrics in some\r\nnaturally deformed limestones, with a view of testing the\r\ngeological applicability of experimentally deduced origins\r\nof such fabrics in these materials. Flexurally folded\r\nlimestones have been used to make comparisons between experiment and nature, by taking advantage of the approximately known character and variation of strain in these structures and using this information to deduce theoretically the deformation fabrics from place to place to compare with those actually observed in the structures. Two kinds of fabric problems are treated, ones dealing with gross changes in crystal orientation accompanying large strain, and those treating the origin of twinning lamellae in carbonate rocks in relation to applied stress, the so-called dynamic analysis. An extension of this analysis is made which allows quantitative information as to rock strain due to twinning (and translation gliding) to be obtained from thin sections.\r\n\r\nCurrent theoretical treatments used in predicting fabric changes with strain in marble are found inadequate for predicting fabric changes with strain in flexure folds.\r\nExact derivations of these fabrics for folds have not been\r\nmade. Instead, an implication of a more general theory\r\ntreating development of fabrics in metal aggregates is used\r\nto derive approximately the changes in c-axis orientations\r\nwith large strain by analogy with fabrics obtained from\r\nexperimental deformed Yule marble. Well defined fabric\r\nchanges with large strain involving both twinning and\r\ntranslation gliding in individual crystals have not been\r\nobserved in the folds studied. \r\n\r\nPredicted results for the dynamic analysis of an aggregate with isotropic c-axis distribution are derived with special reference to one of the folds studied. The stress distribution in plane strain is calculated for the structure starting with an already partly folded unconfined\r\nlayer of circular cross-section, and assuming it to be\r\nloaded elastically with simple compressive forces applied\r\nin the limbs directed normal to the axial plane. Twinning\r\ndeformation in individual crystals is treated by assuming\r\nthat the law of maximum resolved shear stress determines an\r\nactive twin set in each grain. The results obtained are\r\ncompared favorably with those observed in a natural fold.\r\n\r\nDeformation fabrics from two small folds are given.\r\nThe first fold occurs in a large anticlinorium in western\r\nWashington County, Maryland, in thinly bedded limestones\r\nand shales of the Silurian McKenzie Creek formation. The\r\nsecond is a drag fold on the eastern limb of a north-trending anticline in Carboniferous limestones and shales\r\nlocated in upper Darwin wash, Darwin Hills, Inyo County,\r\nCalifornia. In the Maryland fold, c-axis fabrics obtained\r\nfrom the axial region show no preferred orientation due to\r\ndeformation, but a dynamic analysis of the twinning lamellae\r\nis in good agreement with that expected in theory. The dynamic analysis is shown to be sensitive in depicting\r\nsmall changes in twinning deformation throughout portions\r\nof the body examined. The strains due to twinning are\r\ncompatible with bending in part of the structure. More\r\nquantitative comparisons of the observed and expected deformation have shown that under a derived system of stress\r\nat the axial plane, twinning deformation in 80% of the\r\ngrains in the aggregate has followed the law of maximum\r\nresolved shear stress. The amount of twinning strain within\r\nindividual crystals varies with their orientation in the\r\nstress field. The calculated visible (twinning) strains of\r\nabout 0.01 are considerably less than the strains computed\r\nfrom the geometry of the fold of 0.25, and much of this\r\ndiscrepancy may be due to fracturing (slip on planes parallel to bedding) during folding.\r\n\r\nIn the fold from Darwnn wash, observed fabrics cannot be related simply to the megascopic deformation in the fold. Preferred orientations of c-axes are thought to be partly due to veining in t he rock. Fabric changes due to twinning are however qualitatively correlated with shortening in the fold perpendicular to the axial plane, and a shear similar to that necessitated by the relation of the drag fold to the major anticline with which it is associated. Calculated visible strains are considerably less than those approximately deduced from fold geometry, but can be partially correlated with the observed deformation in the structure. Analysis of the deformation in nonhomogeneously strained individual crystals of these aggregates (Appendix II) shows that in addition to e{0112} twinning, translation gliding has occurred on most types of glide planes deduced for calcite from laboratory experiments. Microscopically these rocks appear to have undergone large deformation, exhibiting local cataclastic texture, much twinning and warping of individual crystals. However, well defined formation fabrics due to large strain have not been observed in them.\r\n\r\nA second part of this investigation has dealt with the so-called nontwinned lamellae in calcite and dolomite. From these studies it has been concluded that such structure\r\nare extremely thin (a few microns) but otherwise normal twin lamellae parallel to e{0112} in calcite and\r\nf{0221} in dolomite, and are for this reason renamed microtwinned lamellae. In addition to interference colors,\r\nthese lamellae exhibit four different types of interference\r\nfringes. A new method is presented, which utilizes the optical properties of the twins, for obtaining the\r\norientation of lamellae inclined at small angles to the\r\nplane of a thin section. The utility of this technique\r\nlies in the fact that it may be used to eliminate the\r\ncentral \"blind-spot\" in twin lamellae fabric diagrams.\r\nSome measurements of twin thicknesses, made using the new\r\norientation method, are given, together with calculations\r\nwhich show that only an average and not a cumulative optical\r\nthickness for a stack of lamellae superposed in thin section may be obtained using the method.\r\n", "publication_date": "1962", "thesis_type": "phd", "thesis_year": "1962" }, { "id": "thesis:1068", "collection": "thesis", "collection_id": "1068", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03232006-104828", "primary_object_url": { "basename": "Benson_cs_1960.pdf", "content": "final", "filesize": 27289939, "license": "other", "mime_type": "application/pdf", "url": "/1068/1/Benson_cs_1960.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Stratigraphic Studies in the Snow and Firn of the Greenland Ice Sheet", "author": [ { "family_name": "Benson", "given_name": "Carl S.", "clpid": "Benson-Carl-S" } ], "thesis_advisor": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-B" }, { "family_name": "Sharp", "given_name": "Robert P.", "clpid": "Sharp-R-P" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe Greenland ice sheet is treated as a monomineralic rock formation, primarily metamorphic, but with a sedimentary veneer of snow and firn. This sedimentary member is perennial above the firn line, and the classical methods of stratigraphy and sedimentation can be profitably applied to it.\r\n\r\nDuring a 4-year period 146 pit studies and 288 supplementary Rammsonde profiles were made along 1100 miles of over-snow traverse (Fig.1). Temperature, density, ram hardness, and grain size were measured in the strata exposed in each pit.\r\n\r\nStratification of snow results from variations in the conditions of deposition and is emphasized by subsequent diagenesis. Summer layers are coarser-grained and have generally lower density and hardness values than winter layers; they may also show evidence of surface melt. The onset of fall is usually identified by an abrupt increase in density and hardness accompanied by a decrease in grain size. This stratigraphic discontinuity is used as the annual reference plane.\r\n\r\nStrata in the upper 10 to 20 meters compose a succession of annual sequences which are preserved in recognizable form for at least several decades. Correlation of annual layers between pits, spaced 10 to 25 miles apart along the traverse of Figure 1, gives a picture of annual accumulation during the past 5 to 20 years for western Greenland between 69 and 77\u00b0N. The control established by these data, together with information from earlier expeditions (primarily those of Koch-Wegener and DeQuervain) and from permanent coastal meteorological stations, have been used to make a map showing the distribution of gross annual accumulation, essentially the equivalent of annual precipitation, for the entire ice sheet (Fig. 30). In general, the accumulation contours follow the north-south trend of the coast lines, with extremes of less than 10 cm H2O in the northeast and more than 90 cm H2O per year in the south; the average for the ice sheet is 34 cm H2O per year. The zone of maximum precipitation lies close to the coast in two regions, one on the east coast between Angmagssalik and Scoresbysund, the other on the west coast between Upernavik and Thule.\r\n\r\nIn addition to the existence of a useful stratigraphic record four diagenetic facies are recognized on the ice sheet.\r\n\r\n(1) The ablation facies extends from the outer edge, or terminus, of the glacier to the firn line. The firn line is the highest elevation to which the annual snow cover recedes during the melt season.\r\n\r\n(2) The soaked facies becomes wet throughout during the melting season and extents from the firn line to the saturation line, i.e., the uppermost limit of complete wetting. The saturation line is the highest altitude at which the 0\u00b0C isothermal surface penetrates to the melt surface of the previous summer.\r\n\r\n(3) The percolation facies is subjected to localized percolation of melt water from the surface without becoming wet throughout. Percolation can occur in snow and firn of sub-freezing temperatures with only the pipe-like percolation channels being at the melting point. A network of ice glands, lenses, and layers forms when refreezing occurs. This facies extends from the saturation line to the upper limit of surface melting, the dry-snow line. Negligible soaking and percolation occur above the dry-snow line.\r\n\r\n(4) The dry-snow facies includes all of the glacier lying above the dry-snow line, and negligible melting occurs in it.\r\n\r\nThe saturation line can be identified by discontinuities in temperature, density, and ram hardness data, and it may also be located by examination of melt evidence in strata exposed on pit walls. It is as sharply defined as the firn line; but the dry-snow line, although determined by the same methods, is an ill-defined transition zone 10- to 20-miles wide.\r\n\r\nThe facies represent a response to climate, therefore changes in the location of facies boundaries may be used as indicators of secular climatic change. Since facies are not restricted to the Greenland ice sheet, they provide the basis for a general classification of glaciers. This \"facies classification\" is areal in nature and gives a greater resolution of characteristics than Ahlmann's \"geophysical classification.\" In particular, the \"facies classification\" permits subdivision of large glaciers which span the entire range of environments from temperate to polar. Ahlmann's useful distinction between temperate and polar glaciers takes on new meaning in the light of glacier facies. Thus, a temperate glacier exhibits only the two facies below the saturation line whereas one or both of the facies above the saturation line are present on polar glaciers. An attempt has been made to map the distribution of facies on the Greenland ice sheet (Fig. 48).\r\n\r\nThe distribution of mean annual temperature on the ice sheet may be approximated by gradients with respect to altitude and latitude of 1\u00b0C/100m and 1\u00b0C per degree latitude respectively. The altitude gradient is controlled by strong outgoing radiation, producing deep inversions and katabatic winds. The katabatic winds are warmed adiabatically as they descend along the surface of the ice sheets and this is the primary control determining the temperature gradient along the snow surface. The latitude gradient is based on temperature measurements made above 2000 m on the ice sheets and on average values from meteorological stations spanning 20\u00b0 of latitude on the west coast. A contour map of isotherms based on these gradients compares well with temperature values obtained from pits on the ice sheet. (Fig. 40).\r\n\r\nThe densification of snow and firn is discussed for the case where melting is negligible. The assumption is that accumulation remains constant at a given location and, under this assumption, the depth-density curve is invariant with time as stated by Sorge's law. As a layer is buried it moves through a pressure gradient under steady-state conditions, and it is assumed that the decrease in pore space with increasing load is simply proportional to the pore spaces, i.e., [...] where [...] = specific volume of firn ([...] = firn density), [...] = specific volume of ice = 1.09 cm3/g, [...] = load at depth z below the snow surface and m = a constant which depends on the mechanism of densification. The depth-density equation obtained from equation 8 is [...] where K = [...], [...] = void ratio for snow of density [...], and [...] = void ratio for snow of density [...], [...] = density of snow when [...] = 0.\r\n\r\nThe consequences of the assumption in equation 8 compare favorably with observation. A fundamental change in the mechanism of densification is recognized within 10 m of the snow surface. The concept of a \"critical density\" is introduced. Before the density of snow attains the critical value it is compacted primarily by packing of the grains. The critical density represents the maximum value obtainable by packing and further compaction must proceed by other mechanisms. The rate of change of volume with increasing load decreases by a factor of 4 when the critical density is exceeded. The same equations hold in the case where melt is not negligible but the rates of densification are higher.\r\n\r\nBauer's (1955) estimate for the balance of the ice sheet is revised. Two corrections are applied: (1) the average annual accumulation value of 31 cm H2O originally estimated by Loewe (1936) is revised to 34 cm H2O as a result of this study; (2) the relative areas of ablation and accumulation zones in Greenland north of 76\u00b0N are more accurately defined. The net result is a slightly positive balance which is interpreted to mean that the Greenland ice sheet is essentially in equilibrium with present day climate.\r\n", "doi": "10.7907/G7V2-0T57", "publication_date": "1960", "thesis_type": "phd", "thesis_year": "1960" } ]