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The morphology and internal geometry of a mudflow deposit on the mainland slope of the Santa Barbara Basin are defined using high-resolution seismic-reflection data in combination with core samples. Sediment failure occurred on a 4° slope in the uppermost part of late Quaternary well-bedded slope deposits. The failure zone extends from water depths of 374-510 m near the base of slope, occupies an area of 4 km2, and involved the translation of 0.01-0.02 km3 of sediment. Major geomorphic features of the mudflow deposit include a headscarp 6-8 m high, a scar 50-700 m wide, and a main body 1 km long and 12 m thick. The hummocky surface of the mudflow deposits, their chaotic internal structure, and the bulbous toe tapering upslope to a thin tail are consistent wit mass flow involving extensive internal deformation. Sediment failed in stages, ending with upslope retrogressive retreat of the headwall along the east side of the failure zone. Known sedimentation rates of 0.8-1.4 m/k.y., as well as the presence of a thin (0.15-0.5 m thick) sediment cap resting atop the scar surface, indicate that the failure probably occurred within the past few centuries. A geotechnical analysis incorporating the results of both static and dynamic triaxial strength tests shows that the failure was probably caused by a strong (M 7.5) nearby earthquake. The weakened sediment that remained after earthquake shaking continued to flow down the gentle basin slope under the stresses generated by gravity alone. The analysis also shows that much of the slope sediment is marginally stable and that additional mudflows will probably occur during future strong seismic shaking.

The Mississippi Canyon is one of several large canyon systems which have developed seaward of large rivers around the shelf margin of the Northern Gulf of Mexico. High-resolution geophysical and borehole data are combined to re-evaluate canyon geometry and sedimentology. Incision of the canyon appears to have taken place prior to 30,000 years BP. Canyon widening by slope failure and mass-movement processes resulted in arcuate re-entrants containing slumped debris separated by residual knolls. Much of the sediment associated with canyon formation and widening was transported down-slope, by-passing the upper canyon. Thick, laminated pro-deltaic sediments, greater than 30,000 years old, comprise the basal canyon fill. Rapid deposition along the canyon axis began about 19,000 years BP, ap arently associated with down-canyon mudflows from a nearby lowstand delta. As canyon filling progressed, mass-movement processes declined, resulting in interbedded pro-deltaic and debris flow sediments. The sediment fill was deposited in a complex cut and fill sequence suggesting a much older canyon than previously thought. Deltaic sedimentation retreated northward away from the canyon at about 7,500 years BP, and since that time a Holocene pelagic drape has been deposited.

A large outwash complex occupies a northwest-southeast trending intermorainic low-land in northeastern Illinois. The complex can be divided into four assemblages arranged in zones paralleling the margin of the West Chicago Moraine on the east. 1) The marginal assemblage occurs along the margin of the moraine and consists of gravelly mud flows, fluvial sand and gravel in large, deep channels, and lacustrine muds deposited in shallow basins developed on mudflow surfaces. 2) The proximal assemblage occurs in a 1-km-wide band lying west of the moraine. It consists of cobble gravels in crude, horizontal strata deposited on longitudinal bars and cross-bedded sand and fine gravel deposited in interbar channels as migrating dunes or accretionary wedges during low flow conditions. 3) The media assemblage occurs in a 1-km-wide band in the center of the intermorainic lowland and consists of cross-bedded sands and fine gravel deposited on transverse bars or interbar channels, coarser gravels deposited on longitudinal bars, and ripple-bedded sands and silts deposited in inactive channels or pools of active channels during low flow conditions. 4) The distal facies underlies the other assemblages of the complex and consists of laminated lacustrine muds that accumulated in one or more large proglacial lakes, and fine-grained cross-bedded sands deposited in a braided stream system developed on the eroded lake plain after it was drained. Sediments were derived from the West Chicago Moraine and were carried perpendicularly away from it until they reached the center of the lowland where they were transported southeasterly down the axis of the intermorainic trough.

Gravity-displaced carbonate sediments on the lower slope and basin floor of a Bahamian intra-platform basin were studied using closely-spaced sediment cores up to 5 m in length, 1500 km of precision depth survey, and 3.5 kHz seismic surveys. Based on sedimentary structures and textures of these clastic carbonates, three main types were identified: 1) clean, graded sand and rubble (turbidity-current deposits); 2) massive, poorly sorted sand and rubble (deposits of grain flow or turbidity currents); and 3) muddy rubble and pebbly mud (debris flow and mudflow deposits). These deposits make up nearly 25 percent by volume of the upper 5-7 m of the basinal sediments, with the remainder comprised of peri-platform ooze. Compositionally, the clastic carbonates contain 50-70 percent shallow-wat r materials derived from the adjacent carbonate platform and 30-50 percent chalk lithoclasts and fauna derived from the slope and basin floor. Three individual clastic layers were mapped in the northern part of the basin. Two are turbidites. The third, a composite of pebbly mud, muddy rubble, graded rubble and sand is interpreted as a debris flow deposit with a turbidite on top. The two turbidites have volumes on the order of 107m3. Deposition of these turbidites occured on the basin floor within 10-15 km of basin entry, as lobe-shaped bodies that are thickest near the source area at basin entry and thin rapidly basinward. The third layer covers nearly the entire basin floor, 6400 km2 and has a volume in excess of 1017m3. Unlike the turbidites, this layer cannot be traced to a point source at the mouth of a gully. Rather, it seems to have descended the entire northern ba in-slope in a broad front 20-30 km wide in sheet form extending well out onto the basin floor. Throughout the densely cored study area, the flow was wide enough that its two wings could maintain distinctly different composition. After traveling 100 km across the basin floor as a sheet flow, the denser, muddy rubble (debris flow) became "channeled" by the axial valley, while the closely following turbidity current covered the whole basin floor. Eventually, the entire flow became channeled as it traveled out Exuma Sound through the axial canyon connecting to the abyssal floor of the Atlantic Ocean. Nannofossil zonation and planktonic foraminiferal data suggest this layer was deposited 80,000-120,000 yrs. B.P. when sea level was lowering from the Sangamon high-stand.

A giant armored mud boulder 71 by 70.5 by 60 cm was formed and transported on the surface of recent Mount St. Helens mudflows. This armored mud ball is the largest recorded in the geologic literature and the first from volcaniclastic terrane.

A coarse-grained sequence of turbidite-conglomerates at Wheeler Gorge, California, was deposited by a series of high density, highly fluid underwater flows into deep water. Inverse grading is developed at the base of each conglomerate trait within the sequence, and one unit forcibly intruded shales to form graded sills. One sill is over 100 feet long. The development of reverse grading may in part be explained by Bernoulli's principle, whereby pressures near the boundary of deposition tend to drive the large particles upward. Bernoulli's principle relates the velocity in a fluid system to the pressure in the fluid. The resultant of the pressures is a net upward or inward pressure away from the boundary which operates most effectively on the largest particles. The "Bernoulli boundary layer effect" may explain reverse grading in coarse-grained turbidite deposits, in mudflows, possibly in ignimbrite layers, and in igneous intrusions of the "Muskox type" which have boundaries that are finer-grained than their interior parts.

A sequence of coarse clastic sediments of New Red Sandstone age in western Scotland was probably deposited by alluvial fan (mudflow, streamflood and braided stream), playa and floodplain (low and high-sinuosity channels) processes. Within the alluvial fan group the mudflow deposits are usually laterally persistent, flatbedded paraconglomerates. Individual mudflow units only rarely show basal erosion surfaces. The streamflood deposits consist of laterally impersistent orthoconglomerates and coarse sandstones which often fill channels as large or very large-scale cross-stratified sets. The braided stream deposits are usually sandstones and fine-grained, well-sorted orthoconglomerates with an abundance of trough cross stratification and intraformational pebbles. The braided stream conglomerates, unlike the mudflow and streamflood conglomerates, show no significant relationship between maximum particle size and bed thickness. The playa deposits show alternations of thin, mudcracked mudstones and laminated or rippled sandstones. The deposits of ephemeral, low-sinuosity floodplain rivers are identified as relatively thin, coarse-grained fining-upwards cyclothems in which both fine and coarse members are laterally extensive and there is little lateral variation in structure, thickness or lithology. There is usually a caliche profile capping the fine member. In contrast, thicker, finer-grained, structurally and lithologically more complex cyclothems probably accumulated from high-sinuosity floodplain systems. Alluvial fan (piedmont) sequences show a textural and structural evolution from mudflow up through streamflood to braided stream deposits. The time trend through the laterally equivalent floodplain sequences is from low to high-sinuosity and less ephemeral stream systems. The piedmont trend probably reflects a geomorphic maturing of the basin margins while the floodplain trend suggests an additional climatic change towards less arid conditions. Either trend is consistent with conformably overlying marine (Jurassic) deposits.

Statistical parameters of the granule-to-clay size-frequency distribution efficiently differentiate till from alluvial-fan deposits and from outwash deposits. Discriminant functions utilizing mean, standard deviation, skewness, and kurtosis also separate the three types of sediment. As a test of the method, samples of fossil mudflow were studied; they plot in the area of alluvial-fan deposits.

Numerous tabular bodies of sedimentary rock cut discordantly through bedded Oligocene volcaniclastic sediments along the coast at Oamaru, South Island, New Zealand. Most such dikes represent infilling of irregular fissures which opened spasmodically along the crests of submerged volcanogenic mounds. Infillings predominantly comprise biogenic debris in a wide variety of texture and composition. Dikes are multilayered, with layers either parallel to the walls or at various angles. Layers of different lithotypes, phases , reflect significant temporal differences between episodes of infilling. Layers of similar lithotypes, pulses , reflect relatively short temporal differences or fluctuations in the filling process during a single episode of infilling. Processes of infill range from gravitationally-induced cohesionless grain flow and viscous mudflow to hydrodynamic injections resulting from opening and closing of the fissures. Dike microfacies represent seafloor sediments from probable Lower Oligocene into Lower Miocene time. Some phases reflect transient deposits that are not present in the normal stratigraphic sequence of the coastal region. All fissures did not open at the same time or always follow the same routes, and a definitive regional sequence of phase emplacement cannot be determined.

An origin by subaqueous mudflows is proposed for unsorted sediments previously considered to be tillites. These sediments are in the Carboniferous Kullatine Formation at the northern end of the Manning-Macleay Basin in northeastern New South Wales. The lensoidal nature of the beds and the general lack of lateral continuity of the tilloids as a whole, along with the presence of large contorted masses of underlying sediments, makes it difficult to accept the earlier hypotheses. Grain size distribution, roundness, sphericity, and composition of the tilloid and water-sorted sediments show marked similarities and support a mass-movement origin for the tilloid by suggesting local mixing of the water-sorted sediments. Linear elements in the fine fraction and the contorted masses of sediments contained in some beds suggests that a small number of the mudflows traveled in a laminar fashion; however, the majority of the mudflows probably traveled in a turbulent manner. Viscosity, controlled by the proportion of sand in the fine fraction of the mudflow, appears to be the factor controlling the flow mechanism. Pebble fabric data indicates that orienting forces in a subaqueous mudflow act on the broad faces and long edges of the pebbles, rather than on the long axes. In a fabric diagram, the long axes of the pebbles are contained in a broad girdle that dips in an upflow direction. Thin ends of most of the pebbles point upflow. Approximately 4 percent of the sediments of the Kullatine Formation were involved in subaqueous mudflows. This figure represents a total of about 5.51010 cubic meters of consolidated sediment.

Logarithmic plots of the coarsest 1-percentile grain size (C) and the median grain size (M) of alluvial-fan deposits make distinctive patterns for samples from western Fresno County, Calif. The CM pattern for the tractive-current sediments parallels the limiting line C = M and swings upward where C is about 1500 microns. The mudflow CM pattern is rectilinear and approximately parallels the line C = M. C is about 40 to 80 times M along the axis of the mudflow pattern.

An alluvial fan sequence in the southern Arrow Canyon Range, Nev., consists of an earlier mudflow and a younger stream deposit. Particles of both phases have an exponential decline in size away from the source area. The mudflow has a steeper curve of particle-size decline and a lower correlation coefficient than the stream deposit. The stream deposit is largely the result of reworking of the older mudflow, but has a consistently lower particle size caused by weathering and splitting of the particles. A general increase in the rod- and disc-shaped pebbles downstream is due to transportation in traction and suspension, respectively. Fan head entrenchment is the result of a change from mudflow to stream conditions and the development of a new fan profile.

Computer simulation of the motion of particles in a viscous fluid in laminar flow shows that strong long-axis fabrics may develop in mudflows in a short period of time. The rate at which the fabric develops in any one situation depends on the velocity gradient. The viscosity of the mudflow one of the main factors controlling the velocity gradient, is increased considerably by the clasts contained in the matrix Fabric development is cyclical and begins as a vague girdle dipping upstream. At the same time a single mode develops, centered on the girdle, and gradually increases in intensity until a maximum is reached when the plunge of the mode is horizontal. The fabric from this point degenerates in reverse order, first to a weak girdle dipping downstream, and then to a fabric similar to the initial fabric when the particles have completed a half cycle of motion. The process then begins again. The strength of the fabric depends on the instant at which the mudflow is arrested. Even though most mudflows travel in a turbulent manner, the fabric is developed in the final stages as the velocity of the flow decreases, and it passes to a laminar phase before coming to rest. Limited experiments and simulations show that a C-axis fabric should also develop with a single vertical mode and girdle transverse to the flow direction. Settling of the clasts under gravity after the flow has come to rest probably leads to a strengthening of the C-axis fabric, as clasts would tend to reorient themselves with their plane of maximum projection (the A, B plane) normal to the force of gravity. The Permian Pagoda Formation in Antarctica consists largely of tillite but contains a small number of beds deposited from mudflows. Four A-axis fabrics were measured from the mudflow units and were found to be similar to long-axis fabrics produced by the simulations. All four have dipping girdles, and two display a central mode. When compared with till fabrics from the same section the mudflow fabrics can be distinguished because of the girdles. Had the mudflows been arrested at a stage of maximum fabric development, it would be impossible to distinguish them from most till fabrics. In this situation the problem may be clarified by measuring several fabrics at different levels in the flow. Because the velocity gradient decreases upward the strength of the mudflow fabrics should be dif erent at different levels. An attempt to exploit this method in the field met with very limited success, probably because the change in velocity gradient upward through the mudflow was too small. C-axis fabrics developed by mudflows have vertical modes while their counterparts in till fabrics plunge steeply in a downstream direction. It is concluded that clast fabric could be a valuable tool in determining the origin of diamictites, but more field data are needed.