Flood Hypothesis Research Articles

Field evidence for disequilibrium dynamics in preserved fluvial cross-strata: A record of discharge variability or morphodynamic hierarchy?

Bedforms preserved in the rock record can provide detailed information on the morphologies and hydrodynamics of ancient fluvial systems on Earth and other planets. Existing process–product relations for bedform preservation assume that fluvial cross strata reflect conditions under which bedforms were equilibrated with the prevailing flow, i.e., steady-state conditions. However, recent theoretical and experimental observations indicate that enhanced bedform preservation can occur in non-steady state, or disequilibrium, conditions, and it is currently unclear how prevalent disequilibrium dynamics are in preserved fluvial strata at outcrop scale. Here we explore whether steady-state assumptions are appropriate for ancient fluvial systems by evaluating the nature of bedform preservation in well studied fluvial deposits of three Upper Cretaceous (Turonian and Campanian) geologic formations in central Utah, USA: the Blackhawk Formation, Castlegate Sandstone, and Ferron Sandstone. In the field, we made systematic measurements of dune-scale cross-strata to quantify the extent to which preserved cross-sets reflect dune preservation in steady-state conditions. Across the three formations, consistently low coefficients of variation in preserved cross-set thicknesses of 0.25–0.5 are inconsistent with bedform preservation in steady-state conditions, and instead point to fluvial systems in which enhanced bedform preservation occurred in disequilibrium conditions.Enhanced bedform preservation in dune-scale cross-stratification can be explained by two independent hypotheses: the effect of flashy flood hydrographs on bedform preservation (flood hypothesis) or bedform preservation in the presence of larger migrating barforms (hierarchy hypothesis). We estimated bedform turnover timescales to quantitatively assess these competing hypotheses and contextualize their implications. Under the flood hypothesis, field measurements are consistent with enhanced bedform preservation driven by flashy flood hydrographs with flood durations ranging on the order of hours to a few days, which are consistent with perennial fluvial systems subject to heavy rains and tropical storms. Alternatively, under the hierarchy hypothesis, field measurements are consistent with bedform climb angles that range from 10−2 to 10−1, reflecting rapid bar migration. Our work provides a novel way of investigating fluvial discharge variability in the geologic past, and we outline the potential next steps to disentangle the relative controls of flow variability and morphodynamic hierarchy in controlling bedform preservation in ancient fluvial systems.

Evaluating the impact of Black Sea flooding on the Neolithic of northern Turkey

Originally formulated based on marine geological research concerned with the timing and tempo of the Black Sea infilling, the Black Sea flood Hypothesis (BSfH) argues that this process was a catastrophic event ~7150 BP that greatly impacted the prehistoric peoples who lived along the ancient shoreline. The resulting mass migration of peoples led to great transformations across Europe and southwest Asia. Continued research in the region has challenged the timing and impact of the event, arguing instead that it was neither sudden nor catastrophic. However, the BSfH continues to be invoked as a plausible explanation for the lack of early Holocene or Neolithic period sites in northern Turkey. Results from spatial modelling along the Turkish coast suggest that the explanatory power of the BSfH to explain this absence is exaggerated. Rather, other environmental and social factors must be considered in explaining the complete lack of early Holocene sites across the region.

Holocene marine transgression in the Black Sea: New evidence from the northwestern Black Sea shelf

For two decades, the timing and rate of Holocene marine transgression and the level of the Black Sea prior to the transgression has been the focus of many geological, palaeoecological and archaeological studies. The potential importance of confirming or rejecting the catastrophic flood hypothesis by refining the chronology of the marine transgression and determining the water level of the early Holocene Black Sea (Neoeuxinian) lake is the aim of many ongoing Black Sea palaeoecological studies.In this report we review previous studies and present new data on the early Holocene marine transgression obtained from multidisciplinary studies of several cores from different parts of the Black Sea. Core 342 from the edge of the Dniester paleovalley on NW shelf is particularly important because it provides wood and leaf material from several peat and muddy peat beds, each up to ∼10 cm thick, inter-layered in a coastal succession with mud, clay, and shell coquina. AMS ages for wood fragments and sedge leaves in the peat layers provide critical new data for calibrating and “re-tuning” of previously published shell and bulk detrital peat ages.Our multi-disciplinary study of geological material recovered from different shelf areas of the Black Sea refines the chronology of the marine transgression and clarifies conflicting interpretations of the water level and salinity of the Neoeuxinian lake prior to the initial Mediterranean inflow (IMI) and transgression of Mediterranean water in the Holocene, We find that: (1) The level of the Late Neoeuxinan lake prior to the early Holocene Mediterranean transgression stood around −40 m bsl but not −100 m or more as suggested by advocates of catastrophic/rapid/prominent flooding of the Black Sea by Mediterranean water. (2) At all times, the Neoeuxinan lake was brackish with salinity not less that 7 psu. (3) By 8.9 ka BP, the Black Sea shelf was already submerged by the Mediterranean transgression. An increase in salinity took place over 3600 years, with rate of the marine water incursion being estimated in the order of 0.05 cm–1.7 cm a−1. (4) The combined data set of sedimentological characteristics and microfossil data establish that the Holocene marine transgression was of a gradual, progressive nature in the early Holocene.

Holocene book review: Geology and Geoarchaeology of the Black Sea Region: Beyond the Flood Hypothesis

Holocene book review: Geology and Geoarchaeology of the Black Sea Region: Beyond the Flood Hypothesis

Deriving probabilistic regional envelope curves with two pooling methods

Summary A probabilistic regional envelope curve (PREC) assigns a recurrence interval to a regional envelope curve. A central point of this method is the determination of homogeneous regions according to the index flood hypothesis. A flood discharge associated with the recurrence interval (PREC flood quantile) is estimated for each gauge of a homogeneous region. In this study, the influence of two pooling methods on PREC for a large group of catchments located in the south-east of Germany is investigated. Firstly, using cluster analysis, fixed homogeneous regions are derived. Secondly, the Region of Influence (RoI) approach is combined with PREC. The sensitivity of PREC flood quantiles with respect to pooling groups is evaluated. Different candidate sets of catchment descriptors are used to derive pooling groups for both pooling methods. Each pooling group is checked by a homogeneity test. PRECs are then constructed for all homogeneous regions. The ensemble of PREC realisations reveals the sensitivity of the PREC flood quantiles. A comparison with the traditional index flood method ascertains the suitability of the pooling methods. A leave-one-out jackknifing procedure points out a similar performance of cluster analysis and RoI. Furthermore, a comparison of different degrees of heterogeneity for deriving pooling groups reveals that the performance of PREC for ungauged catchments decreases in more heterogeneous pooling groups.

A meltwater origin for Antarctic shelf bedforms with special attention to megalineations

The geomorphology of troughs crossing the Antarctic shelf is described and interpreted in terms of ice-stream hydrology. The scale of tunnel channels on the inner shelf and the absence of sediment at their mouths are taken to infer catastrophic drainage. Drumlins on the inner and outer shelves with pronounced crescentic and hairpin scours are also interpreted as products of catastrophic flow. Gullies and channels on the continental slope and turbidites on the rise and abyssal plain point to abundant meltwater discharge across the shelf. Attempts to explain this morphology and sedimentology in terms of release or discharge of meltwater by pressure melting, strain heating, Darcian flow, or advection in deforming till are shown to be unrealistic. We suggest that meltwater flow across the middle and outer shelves might have been in broad, turbulent floods, which raises the possibility that megascale glacial lineations (MSGL) on the shelf might originate by erosion in turbulent flow. This possibility is explored by use of analogs for MSGL from flood and eolian landscapes and marine environments. An extended discussion reflects on objections that stand in the way of the flood hypothesis.

The timing and evolution of the post-glacial transgression across the Sea of Marmara shelf south of İstanbul

High-resolution seismic reflection profiles and analyses of the sedimentary substrate at the Sea of Marmara (SoM) entrance to the Strait of İstanbul (SoI, Bosphorus) provide a detailed record of the transgression that took place after the SoM reconnected with the Mediterranean. The sediments progressively fill a paleo shelf valley that incised the margin from the SoI to the shelf break at the time of the pre-Holocene lowstand. We map seven seismic reflection units that can be confidently correlated to sediment cores by lithology and physical properties. Sediments in the cores are dated by radiocarbon methods. Early channel and levee deposits within the paleo valley belong to the Younger Dryas cold stage and record outflow from the Black Sea via the SoI. Small clinoform packages on the valley margin formed in proximity to climbing paleo shorelines. The elevations of these deposits conform to the sealevel history recorded in Barbados corals. The younger part of the succession includes a subaqueous prodelta sourced from the Kurbağalıdere River. Its relatively young age when the Holocene sea had almost reached its modern level suggests that the thick progradational and aggradational clinoform development was primarily a response to sediment supply rather than the filling of expanding accommodation space. Our findings refute the hypothesis of Aksu et al. (Aksu, A.E., Hiscott, R.N., Mudie., P.J., Rochon, A., Kaminski, M.A., Abrojano, T., Yaşar, D., 2002a. Persistent Holocene outflow fromn the Black Sea to the Eastern Mediterranean contradicts Noah's Flood hypothesis, GSA Today 10,(6), 3–7., Aksu, A.E., Hiscott, R.N., Kaminski, M.A., Mudie, P.J., Gillespie, H., Abrojano, T., Yaşar, D., 2002b. Last glacial–Holocene paleoceanography of the Black Sea and Marmara Sea: stable isotopic, foraminiferal and coccolith evidence. Mar. Geol., 190, 119–149.) and Hiscott et al. (Hiscott, R.N., Aksu, A.E., Yaşar, D., Kaminski, M.A., Mudie, P.J., Kostylev, V.E., MacDonald, J.C. Isler, F.I., Lord, A.R., 2002. Deltas south of the Bosphorus Strait record persistent Black Sea outflow to the Marmara Sea since ∼ 10 ka, Mar. Geol., 190, 95–118., Hiscott, R.N., Aksu, A.E., Mudie., P.J., Kaminski, M.A., Abrajano, T., Yaşar, D., Rochon, A., 2007. The Marmara Sea gateway since ∼ 16 ky BP: non-catastrophic causes of paleoceanographic events in the Black Sea at 8.4 and 7.15 ky BP. In Yanko-Hombach,V., Gilbert, A.S., Dolukhanov, P.M. (Eds.), The Black Sea Flood Question, Springer, The Netherlands, 89–117.) that this deposit was supplied from the SoI and that its presence requires a persistent Black Sea outflow since 10 14C ka bp (not corrected from the reservoir age or calibrated).

Late glacial, Holocene and modern dinoflagellate cyst assemblages in the Aegean–Marmara–Black Sea corridor: statistical analysis and re-interpretation of the early Holocene Noah’s Flood hypothesis

Understanding of the history of water exchange between the Mediterranean and Black seas has been hampered by the lack of continuous microfossil records for Holocene cores from the Marmara Sea Gateway (Aegean–Marmara–Black Sea corridor), and by the lack of core-top data linking modern microfossil assemblages with sea surface conditions. Based on molluscs, an abrupt transition from freshwater to marine conditions at ca. 7.5 ka has been postulated, with interpretation of this event as the basis for the story of Noah’s Flood. We have re-examined this hypothesis using organic-walled dinoflagellate cysts that show excellent preservation and moderate to high diversity in Pleistocene–Holocene sediments of the Marmara Sea Gateway. Principle component analysis of 16 core-top samples shows that an assemblage dominated by cysts of autotrophic gonyaulacoids distinguishes the hypersaline Aegean–Mediterranean water (salinity 31–38), whereas heterotrophic protoperidinioids characterise the low-salinity Marmara–Black Sea water (salinity ∼14–25). About 150 samples from eight cores, with multiple radiocarbon ages spanning the past ∼33 000 years, show correlatable major changes in cyst assemblages along the Marmara–Black Sea corridor. Variation in length and shape of gonyaulacoid species processes decreases upcore from basal units where there are no-analogue assemblages of cysts with highly variable spine development. It is shown that these variable and no-analogue assemblages correspond to brackish conditions (salinity ∼4–12) when calibrated against δ 18O data and salinity estimates derived from planktonic foraminifera. Salinity reconstructions indicate that the Aegean and Marmara seas were connected by ∼11 ka when the Marmara Sea was a brackish or low-salinity sea (∼12–17) and that the Black Sea was flowing into the Marmara Sea by at least 10.2–9.5 ka. There is no evidence to support either the idea that the Black Sea was a large freshwater lake suitable for farming in the early Holocene or that a sudden (<500-yr) flooding of the Black Sea by a 100-m-high waterfall of Mediterranean water occurred at 7.5 ka. It is shown that there is a need for precise use of salinity terms when reconstructing the history of saline lakes in the context of Neolithic human occupation so that the likelihood of agricultural settlement can be evaluated realistically.

Catastrophic Flooding of the Black Sea

▪ Abstract Decades of seabed mapping, reflection profiling, and seabed sampling reveal that throughout the past two million years the Black Sea was predominantly a freshwater lake interrupted only briefly by saltwater invasions coincident with global sea level highstand. When the exterior ocean lay below the relatively shallow sill of the Bosporus outlet, the Black Sea operated in two modes. As in the neighboring Caspian Sea, a cold climate mode corresponded with an expanded lake and a warm climate mode with a shrunken lake. Thus, during much of the cold glacial Quaternary, the expanded Black Sea's lake spilled into to the Marmara Sea and from there to the Mediterranean. However, in the warm climate mode, after receiving a vast volume of ice sheet meltwater, the shoreline of the shrinking lake contracted to the outer shelf and on a few occasions even beyond the shelf edge. If the confluence of a falling interior lake and a rising global ocean persisted to the moment when the rising ocean penetrated across the dividing sill, it would set the stage for catastrophic flooding. Although recently challenged, the flood hypothesis for the connecting event best fits the full set of observations.

Last glacial–Holocene paleoceanography of the Black Sea and Marmara Sea: stable isotopic, foraminiferal and coccolith evidence

Multi-proxy data and radiocarbon dates from several key cores from the Black Sea and Marmara Sea document a complex paleoceanographic history for the last ∼30 000 yr. The Marmara Sea was isolated from both the Black Sea and the Aegean Sea during glacial periods when global sea-level lowering subaerially exposed the shallow sills at the Straits of Bosphorus and Dardanelles (i.e. lake stage), and reconnected through both straits during interglacial periods, when rise of global sea level breached the shallow sills (i.e. gateway stage). Micropaleontological data show that during the ‘lake stage’ the surface-water masses in both the Marmara Sea and Black Sea became notably brackish; however, during the ‘gateway stages’ there was a low-salinity surface layer and normal marine water mass beneath. Two sapropel layers are identified in the Marmara Sea cores: sapropels M2 and M1 were deposited between ∼29.5 and 23.5 ka, and ∼10.5 and 6.0 ka, respectively. Micropaleontological and stable isotopic data show that the surface-water salinities were reduced considerably during the deposition of both sapropel layers M2 and M1, and calculation using planktonic foraminiferal transfer functions shows that sea-surface temperatures were notably lower during these intervals. The presence of fauna and flora with Black Sea affinities and the absence of Mediterranean fauna and flora in sapropels M1 and M2 strongly suggest that communication existed with the Black Sea during these times. A benthic foraminiferal oxygen index shows that the onset of suboxic conditions in the Marmara Sea rapidly followed the establishment of fully marine conditions at ∼11–10.5 ka, and are attributed to Black Sea outflow into the Marmara Sea since 10.5 ka. These suboxic conditions have persisted to the present. The data discussed in this paper are completely at odds with the ‘Flood Hypothesis’ of Ryan et al. (1997), and Ryan and Pitman (1999).

Late Glacial to Holocene benthic foraminifera in the Marmara Sea: implications for Black Sea–Mediterranean Sea connections following the last deglaciation

Benthic foraminifera were studied from four gravity cores that penetrated Holocene marine sediments in the Marmara Sea. Morphogroup and assemblage analyses reveal that the Holocene sea-level rise did not result in a catastrophic flooding event as proposed by W.B.F. Ryan and others, whereby well-oxygenated, saline Mediterranean waters rapidly inundated a low-lying low salinity ‘Black Sea Lake’ at ∼7.15 ka (popularly known as the ‘Noah’s Flood Hypothesis’). Rather, the benthic foraminiferal data confirm the hypothesis that the Dardanelles sill was breached by the Mediterranean at ∼12 ka, allowing saline waters to penetrate the Marmara Sea. These saline waters reached the level of the Bosphorus sill at ∼9.5 ka, but were unable to penetrate into the Black Sea until after ∼9.1 ka because of the persistent strong outflow of brackish to fresh water from the Black Sea. The initial colonisation of the Marmara Sea by benthic foraminifera is essentially synchronous with the re-establishment of marine connections through the Dardanelles Strait at ∼12 ka. By ∼10 ka, Ammonia-dominated faunas developed on the strait-exit delta (Δ1) at the southern end of the Bosphorus, and at ∼9.1 ka the appearance of fully marine species documents the establishment of a more stratified water column over Δ1. Finally, the increase in abundance of planktonic foraminifera at the southern exit of the Bosphorus after ∼6.1 ka reflects a decreased volume of outflow water from the Black Sea. Quantitative analysis of benthic foraminiferal morphogroups reveals that the oxygen content of sub-halocline water was low (below ∼1.5 ml/l) throughout the Holocene, and the occurrence of sapropel sediment in the deeper part of the basin suggests bottom waters may have been anoxic at times. After ∼4.5 ka, an increase in benthic foraminiferal oxic morphotypes suggests a reduction in Black Sea outflow and weakening of the halocline. The strong and persistent stratification of the water column in the Marmara Sea throughout the Holocene is entirely incompatible with the ‘Noah’s Flood Hypothesis’.

Persistent Holocene Outflow from the Black Sea to the Eastern Mediterranean Contradicts Noah's Flood Hypothesis

Controversy surrounds reconnection of the Black Sea and Mediterranean during Holocene sea-level rise. This reconnection and its causes have implications for European and Middle Eastern archaeology, paleoclimate, and marine sedimentation; e.g., genesis of organic-rich muds (sapropels). Bill Ryan, Walter Pitman, and co-workers propose reconnection via a catastrophic flood of Mediterranean water into the Black Sea at ca. 7.5 ka, with speculation that this was the historical basis for the biblical story of Noah's Flood. In contrast, this paper suggests a more complex and progressive reconnection over the past 12 k.y. Today, the Black Sea exports considerably more brackish water than the saline inflow it receives from the Mediterranean. There is a stratified, two-layer flow that has a strong effect on aquatic life and seabed sediments. The Sea Gateway (narrow straits of Dardanelles and Bosphorus, and deep intervening Marmara Sea) provides a set of natural flow valves (and sediment traps) that in principle should contain a record of the reconnection. Using ~7500 line-km of seismic profiles, 65 soft-sediment cores, and 43 radiocarbon dates, we recognize a 10-11 k.y. history of low surface- water salinities in the Marmara Sea and northern Aegean Sea. The low-density surface layer promoted uninterrupted water-column stratification and depleted oxygen concentrations at depth and is attributed to persistent Black Sea outflow across the Bosphorus Strait. Seismic data reveal a climbing delta on the middle shelf south of the Bosphorus exit, active only from ca. 10 to 9 ka based on radiocarbon dating of its distal prodelta. The strength of the early outflow is confirmed by the progradation of this delta, and contemporaneous severe water-column stratification leading to deposition of sapropels in basinal areas. Ryan and Pitman's argument for a catastrophic Black Sea flood hinges on the rapid first appearance of euryhaline (Mediterranean) mollusks on Black Sea shelves at ca. 7.5 ka. In our view, this colonization was not a consequence of catastrophic flooding but rather the outcome of a slow establishment of two-way flow in the Bosphorus and a time lag during which the fresher waters of the deep Black Sea were replaced by more saline inflow, eventually allowing marine organisms to colonize the Black Sea shelves.

Possible miocene catastrophic flooding in Egypt's Western Desert

Geomorphic mapping from LANDSAT-MSS images of the Western Desert of Egypt reveals giant flutes sculptured in Eocene limestone plateaus in one large field (225 × 125 km) and one smaller field (60 × 40 km). Plan form and dimensions, distribution, and orientation of the flutes suggest catastrophic flood erosion. In the larger field, several of the flutes coincide with previously mapped outcrops of Cenozoic gravels of an inferred fluvial origin, which lends support to the flood hypothesis, although gravel lithology does not indicate a unique source. The age of the flutes is confined between the end-Miocene cutting of the Nile canyon, which truncates the larger field, and the end-Oligocene drainage west and northwest across Egypt from the Red Sea uplift, a trend transected by and, therefore, older than the larger flute field. A Miocene age (24− ∼ 7 Ma) is proposed. Catastrophic flooding would likely have originated in erosional and/or tectonic release of tectonically dammed or reversed drainage to the south (perhaps far south) of the larger flute field at 27°N.

Possible outburst floods from debris‐covered glaciers in the sierra nevada, california

A sequence of aerial photographs of Mendel Glacier, a debris‐covered glacier in the central Sierra Nevada, California, suggests that at least one outburst flood originated from a subglacial reservoir beneath a prominent mid‐glacier surface depression. By 1962, a ring of crevasses 250 m in diameter was centered within the depression, implying recent ice collapse. In 1972, the crevasses had almost disappeared, and by 1987, a lake of similar area had replaced the crevasse ring. No lake was present in 1995/6. Theoretical examination of ice overburden and hydrostatic pressure at the glacier bed indicate that a subglacial water reservoir may have formed beneath the surface depression prior to 1962. According to theory, as water accumulates within the reservoir, the hydrostatic pressure increases until it is equal to the ice overburden pressure down‐glacier from the reservoir, at which point an outburst flood initiates. Cesium‐137 measurements from the Mendel Glacier outwash plain indicate the post‐bomb‐testing deposition of approximately 20 cm of sand, lending support to the flood hypothesis. The supraglacial lake is ephemeral, and likely reflects relatively high inflow rates or low outflow rates. This sequence of events is possible because the debris cover reduces local ablation rates, forming a depression up‐glacier of the debriscover, which in turn forces water to flow into a subglacial reservoir. As long as the debris content is relatively low (<13% by weight), the reservoir water will eventually float the glacier and initiate an outburst flood. Debris‐covered glaciers should be recognized as potential sources of outburst floods in alpine regions.

Evidence for large-scale subglacial meltwater flood events in southern Ontario and northern New York State

Research Article| December 01, 1990 Evidence for large-scale subglacial meltwater flood events in southern Ontario and northern New York State John Shaw; John Shaw 1Department of Geography, Queen's University, Kingston, Ontario K7L 3N6, Canada Search for other works by this author on: GSW Google Scholar Robert Gilbert Robert Gilbert 1Department of Geography, Queen's University, Kingston, Ontario K7L 3N6, Canada Search for other works by this author on: GSW Google Scholar Geology (1990) 18 (12): 1169–1172. https://doi.org/10.1130/0091-7613(1990)018<1169:EFLSSM>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John Shaw, Robert Gilbert; Evidence for large-scale subglacial meltwater flood events in southern Ontario and northern New York State. Geology 1990;; 18 (12): 1169–1172. doi: https://doi.org/10.1130/0091-7613(1990)018<1169:EFLSSM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Flow-line patterns constructed from the orientation of drumlin long axes are used to infer two major subglacial meltwater floods in southern Ontario and northern New York State. In this interpretation, the flood waters of the first event, the Algonquin, surged southward. In the later, Ontarian event, powerful floods streamed southwestward along the basins of Lakes Ontario and Erie. Bedrock fluting, upstream-pointing noses on escarpments, and tunnel channels give supporting evidence for the regional flood hypothesis. Regional distributions of drift thickness may be explained by this hypothesis. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Drumlins and catastrophic subglacial floods

A number of lines of evidence are shown to be consistent with drumlin formation by catastrophic meltwater floods. Drumlins are associated with landforms related to such floods, and landscapes produced by outburst floods in extraglacial areas contain drumlin-like landforms. Some drumlins, which contain mainly residual materials, are compared to similar forms covering a wide range of scales and are interpreted to be scour remnant ridges produced by the action of horseshoe vortices on subglacial materials. These vortices are a product of flow separation in turbulent fluids and this interpretation implies drumlin formation by meltwater. Other drumlins, called “cavity fill drumlins”, have distinctive shapes that are analogous with infilled erosional marks produced by turbulent, separated flows. These drumlins are interpreted as the infills of cavities eroded upwards into glacier beds by broad, subglacial meltwater sheetflows. The sedimentology and internal structure of the cavity fill drumlins indicate rapid deposition from hyperconcentrated flow. Clast shape, surface texture and lithology are consistent with the short distance of glaciofluvial transport predicted by the cavity fill hypothesis. Estimates of flow discharge (0.6–6 × 10 7m 3/s), total volume of flow (84.1 × 10 3km 3), and flow duration (16–162 days) are given for the catastrophic flood proposed to have produced the Livingstone Like, Saskatchewan, drumlin field. Subglacially derived floods are used to explain the sudden drainage of extraglacial lakes, and major depositional events in proglacial lakes, and it is suggested that they might have contributed to the lid of cold freshwater over the North Atlantic, held to have caused a Late Glacial cooling event. The flood hypothesis requires extensive subglacial lakes to have occurred beneath the Laurentide and Fennoscandian Ice Sheets which, if they existed, must have influenced the form and behaviour of these major bodies of ice.

Catastrophic flood hypothesis for the origin of the Souris spillway, Saskatchewan and North Dakota

Glacial-lake spillways in the midcontinent region consist of narrow, deep trenches connecting proglacial lake basins. Geomorphic and sedimentologic evidence from the Souris and Des Lacs spillways in Saskatchewan and North Dakota indicates a catastrophic drainage of Glacial Lake Regina. The Souris spillway in Saskatchewan is composed of a broad, upper scoured surface 5 to 10 km wide, which merges with the floor of Glacial Lake Regina. The upper surface is longitudinally grooved and mantled with coarse lag deposits. An inner trench, 1 km wide and 20 to 45 m deep, occupies the center of the spillway. The two-level morphology of the spillway probably developed by initial erosion of the upper level, followed by incision of the inner trench, a sequence of events shown by flume experiments performed by Shepherd and Schumm. Near the Saskatchewan and North Dakota border, the flood water bifurcated into two branches as part of the water spilled over a divide into another spillway channel. The two spillways in North Dakota, pre-existing meltwater channels, were occupied and enlarged by the discharge from Glacial Lake Regina. Along the path of the spillways leading to the Glacial Lake Souris basin, water repeatedly breached the sides of the channels, eroding shallow channels leading away from the spillway. Near Minot, North Dakota, a significant amount of the water spilled out toward the east and eroded a plexus of anastomosing channels with streamlined erosional remnants between the channels. Deposits of the flood include huge point bars located at the inside of each channel meander. Internally, the bars generally consist of poorly sorted, indistinctly bedded, coarse gravel containing boulders of resistant and nonresistant lithologies as much as 3 m in diameter. Peak discharge of 1 × 10 5 m 3 /s or more may have been achieved at the outlet of the lake. At this rate, Glacial Lake Regina would have drained rapidly, probably in less than a month. The most likely cause for the rapid drainage of such proglacial lakes as Glacial Lake Regina was high discharge inflow of water from an upstream source along the ice margin.

Effects of a Random versus Pattern Instructional Set in a Contingent Partial Reinforcement Situation

The characteristic response curves of Ss operating under partial reinforcement are well-known. In a two-choice situation, for instance, they start off responding equally to both choices and then increase the proportion of their responses to the most profitable choice. Ordinarily, the final level of response is less than 100% preference for the alternative associated with the most frequent reward. Possibly, Ss try to match the occurrence of the reinforcement, assuming incorrectly that its schedule is patterned. Hence, they will vary their choices between the two alternatives in the expectation of the occurrence of reward at both of them. Flood (6) has hypothesized that the pure type of behavior (100% responding to the most profitable side) will be found in Ss who are convinced of randomness while the mixed type of behavior (trying to anticipate reward on the least profitable side as well) would be obtained when Ss believed there was a patterned arrangement in the occurrence of reinforcement. To test Flood's hypothesis we have varied the instructional sets given to Ss. One group was told that the reinforcements were being manipulated according to a pattern and it was their task to ascertain what this pattern was to get as many rewarded responses as possible. A second group was told that the reinforcements were being manipulated in a completely random fashion, and it was their task to get as many rewarded responses as they could. Accordingly, one would expect the second group to respond more often to the most profitable side, if Ss believed the instructions given to them.

Corrasion by Gravity Streams with Applications of the Ice Flood Hypothesis

Corrasion by Gravity Streams with Applications of the Ice Flood Hypothesis

Corrasion by gravity streams with applications of the ice flood hypothesis. Parts I, II, III.

Corrasion by gravity streams with applications of the ice flood hypothesis. Parts I, II, III.