Abstract Up until the late 1980s geology contributed very little to the study of tsunamis because most were generated by earthquakes which were mainly the domain of seismologists. In 1987–88 however, sediments deposited as tsunamis flooded land were discovered. Subsequently they began to be widely used to identify prehistorical tsunami events, providing a longer-term record than previously available from historical accounts. The sediments offered an opportunity to better define tsunami frequency that could underpin improved risk assessment. When over 2200 people died from a catastrophic tsunami in Papua New Guinea (PNG) in 1998, and a submarine landslide was controversially proven to be the mechanism, marine geologists provided the leadership that led to the identification of this previously unrecognized danger. The catastrophic tsunami in the Indian Ocean in 2004 confirmed the critical importance of sedimentological research in understanding tsunamis. In 2011, the Japan earthquake and tsunami further confirmed the importance of both sediments in tsunami hazard mitigation and the dangers from seabed sediment failures in tsunami generation. Here we recount the history of geological involvement in tsunami science and its importance in advancing understanding of the extent, magnitude and nature of the hazard from tsunamis.

Abstract The Channeled Scabland of east-central Washington comprises a complex of anastomosing fluvial channels that were eroded by Pleistocene megaflooding into the basalt bedrock and overlying sediments of the Columbia Plateau and Columbia Basin regions of eastern Washington State, U.S.A. The cataclysmic flooding produced huge coulees (dry river courses), cataracts, streamlined loess hills, rock basins, butte-and-basin scabland, potholes, inner channels, broad gravel deposits, and immense gravel bars. Giant current ripples (fluvial dunes) developed in the coarse gravel bedload. In the 1920s, J Harlen Bretz established the cataclysmic flooding origin for the Channeled Scabland, and Joseph Thomas Pardee subsequently demonstrated that the megaflooding derived from the margins of the Cordilleran Ice Sheet, notably from ice-dammed glacial Lake Missoula, which had formed in western Montana and northern Idaho. More recent research, to be discussed on this field trip, has revealed the complexity of megaflooding and the details of its history. To understand the scabland one has to throw away textbook treatments of river work. —J. Hoover Mackin, as quoted in Bretz et al. (1956, p. 960)

Abstract To assist U.S. Air Force archaeologists study and preserve cultural sites associated with early Native American inhabitants of the Nevada Test and Training Range, we have determined the late Pleistocene environments of nine playas on the range from surface deposits around the playas. Based on shoreline features such as barrier bars, wave-cut benches, and beach gravel deposits, the playas of Mud Lake, Gold Flat, and Kawich Lake contained pluvial lakes. Based on fossils, palustral clay sediments, paleospring, and seep deposits, the playas of Stonewall Flat, Indian Springs Valley, and Three Lakes Valley contained extensive wetlands. Two playas in Cactus Flat and one at Dog Bone Lake contain none of these surface deposits and are interpreted to have hosted seasonal lakes and grassy meadows, based on modern analogs in the Pahranagat Valley. Radiocarbon dates from Mud Lake, Gold Flat, and Stonewall Flat indicate these environments existed up to the beginning of the Holocene ca. 10,000 years before present (yr B.P.) and would have provided resources of fresh water, fish and game, edible and medicinal plants, fuel, and materials for the construction of shelter. As changing climate conditions from 10,000–8000 radiocarbon yr B.P. forced the contraction and eventual disappearance of these lakes and wetlands, basins with larger surface water budgets probably furnished early inhabitants with useful resources after the pluvial features in the smaller basins had disappeared.

In hopes of shedding light on their genesis, Mima-type soil mounds were investigated at two environmentally and geologically disparate gravelly prairies, Diamond Grove Prairie in southwestern Missouri, and Mima Prairie in the southern Puget Sound of Washington. Mound soils were described, with large volume samples collected at narrow depth increments and laboratory analyses conducted. Results reveal, as predicted, that the soils contain small gravels (≤6 cm) scattered throughout the mound above a basal stone layer of large clasts (>6 cm). The stone layer is exposed across the intermound areas as a pavement. Biomantle principles predicted that mound soils would be texturally biostratified by small burrowing vertebrates into locally thickened, two-layered biomantles, and they are. What was not expected, but might have been predicted by the principles, was the revelation from laboratory data of a second, upper, weakly expressed stone layer of pebbles (≤6 cm). To explain the secondary stone layer we introduce the concept of dominant bioturbator . At both prairies the dominant bioturbator was probably, until geologically recently, a species of the Geomyidae family of rodents, pocket gophers. This animal does not presently inhabit either prairie, but is present nearby. We attribute the secondary, apparently incipient stone layer to new dominants, almost certainly invertebrates, whose textural effects were regularly erased by the earlier (gopher) dominants. These effects are evident and expressed as a new upper biomantle that is now being superimposed upon the old.

We studied low prairie (Mima) mounds and ridges with sorted stone borders separated by broad rubbly soil intermounds in areas near Mount Shasta, northern California. An earlier study ascribed a purely physical origin for these soil features based on a four-stage conceptual model. Mounds were interpreted as periglacially produced clay domes formed in polygonal ground and stone perimeters as loose gravity accumulations in unexplained shallow trenches at dome peripheries. The model was widely cited to account for similar stone-bordered prairie mounds and rubbly soil intermounds in the Pacific Northwest. Our observations and measurements indicate, however, that these mounded landscapes are more complex, and that a polygenetic origin best explains them. We suggest that combined bioturbation, seasonal frost action, and erosion processes, with occasional eolian inputs, best account for the mounds, their well sorted stone borders, and the poorly sorted rubbly soil intermound pavements. We propose a transitional, eight-stage conceptual model to explain this complex landscape. The model may generally explain the origin of other similar strongly bioturbated, cold winter-impacted, erosion-prone mounded tracts in the Pacific Northwest.

The Black Sea basin presents an ideal laboratory for investigations of morphodynamic interplay between response (morphology) and force (processes) associated with shelf sedimentation. Recent studies along the perimeter of the basin have documented the existence of a complex, heterogeneous seafloor varyingly composed of sand, gravel, silt, and clay. Side-scan sonar data are utilized to establish the spatial patterns of bedform types in the area. In addition, a benthic tripod, configured with an acoustic Doppler current profiler, a rotary fanbeam sonar, and a conductivity-temperature sensor was deployed to record seabed dynamics in response to changing forcing conditions. Together, the tripod and side-scan survey data sets provide a complementary basis for deciphering the processes responsible for the observed seafloor morphology. The side-scan sonar data allows for the determination of spatial patterns of bedform length and orientation. In total, 2376 individual large sand wave bedforms were digitized in geographic information systems with mean and modal wavelengths of 72.8 and 15.7 m respectively. The correlation of near-inertial waves (velocity amplitude 12–20 cm/s and period 12–16 h) and bedform geometry suggest that the extensive sand-wave patches imaged across the shelf are affected by active modern processes and may themselves be modern features or perhaps relict features that remain active presently. Progressive vector diagrams of the nearbed mean current flow indicate a component of cross-shelf directed flow, suggesting an enhanced potential for artifact preservation via cross-shelf advection of anoxic bottom waters by the near-inertial flows measured in this study.

Abstract Riverbluff Cave developed near the southern margin of the Springfield Plateau as a single passage between James River and its tributary, Ward Branch. Portions of the cave preserve a general fining-upward sediment sequence, but with highly fossiliferous gravel beds near the middle. These gravel beds include fragments of various vertebrates, including mammoth and horse. Trackways and claw marks are also preserved atop the sediment in numerous locations. Cosmogenic isotope data provide burial dates for some of the sediment layers and fossil remains. The earliest sediment (reverse magnetic polarity) entered the cave at ~1.1 Ma, while the fossiliferous gravel bed is dated at ~0.74 Ma. The overlying laminated silts and clays have normal polarity with a burial date of ~0.65 Ma at the base. Thus, the sediment sequence spans the Matuyama/Brunhes paleomagnetic datum, and records at least 450 ka of sedimentation within the cave.

Lake Manix, in south-central California, was the terminal basin of the Mojave River until the late Pleistocene, when it drained east to the Lake Mojave Basin. Based on new field observations, radiocarbon ages, and soil development, we propose modifications to previously published hypotheses on the timing of the last 543 m above sea level (masl) highstand of Lake Manix, the timing of the first discharge eastward, and the time required to cut Afton Canyon between the two basins. Subtle beach barriers, wave-cut scarps, and lagged beach gravels indicate that Lake Manix reached highstands between 547 and 558 masl at least twice prior to its previously known 543 m highstands. Properties of soils formed on beach barriers at 547–549 masl compared to soils on dated deposits suggest an age of older than 35 cal ka for this highstand. Calibrated radiocarbon ages for three lacustrine highstands at or near 543 masl are ca. 40–35 ka, 33–30 ka, and 27–25 ka. Lake Manix periodically discharged down a drainage presently located on the north rim of Afton Canyon at 539 masl. Soil development estimated from multiple buried soils within fluvial deposits and overlying fan deposits suggests that discharge was coeval with or somewhat older than the 547–549 m highstand, and that fluvial aggradation in this drainageway was followed by a period of relative landscape stability and episodic burial by alluvial-fan deposits. Strath terraces below these highest fluvial deposits, but above the canyon rim, record initial incision of the Lake Manix threshold. Surface and soil properties indicate that they are latest Pleistocene to early Holocene in age, similar to the previously studied strath terraces that are inset well below the rim and below the basal lake sediments. We suggest that the higher straths above the rim formed no earlier than ca. 25 cal ka. We interpret the soils, stratigraphy, and fluvial landforms in the canyon to indicate relatively rapid incision of Afton Canyon to the depth of the bedrock floor of Lake Manix, followed by intermittent, gradual bedrock incision.

A thick sequence (∼177 m) of aggradational deposits was studied in the lower Hope Valley. Valley fill is preserved in a tectonic depression, which is associated with a releasing bend on the active strike slip Hope Fault. Our results indicate that local basin subsidence since the last glacial maximum (LGM) occurred at a rate of 1.4–2.5 mm/yr, which roughly matches the regional tectonic uplift rate. The approximate balance between uplift and basin subsidence resulted in a local late Pleistocene sedimentary pattern that was primarily controlled by climate-induced processes of aggradation and degradation. Here we describe deposits and subsurface sedimentary structures from an exposure located near Glynn Wye on the southern side of the Hope Valley. Sediments at the base of the studied sequence comprise 55 m of lacustrine/deltaic deposits that are overlain by thick fluvial and glaciofluvial gravels. Infrared stimulated luminescence (IRSL) dating on the lake beds yielded an age of 60.3 ∼5.6 ka BP, suggesting late OIS 4 ( oxygen isotope stage ) age for the lake. A subsequent phase of fluvial aggradation buried paleolake deposits under 65 m of glaciofluvial outwash. This was followed by the progression of a glacial advance which deposited a moraine over the top of the sequence. A luminescence age (IRSL) of 32.1 ∼2.6 ka BP from the outwash deposit below the moraine indicates that glaciofluvial aggradation prior to the ice incursion was well advanced during late OIS 3. Postglacial fluvial degradation caused 160 m of incision into the lower Hope Valley, thereby partially excavating the deeper basin fill.

The sand and gravel within the Waipaoa River system of North Island, New Zealand, elucidate the provenance and sedimentary delivery system of an actively deforming continental forearc. In this region, Mesozoic to Cenozoic forearc basin sedimentary successions are being uplifted, eroded, and recycled into younger deposits. The identification of specific characteristics of the drainage basin bedrock can be linked to sediment composition, which in turn can document the processes of provenance mixing and dilution. Despite the proximity of the Waipaoa River to an active volcanic arc (∼250 km), its sediment load includes a relatively small proportion of volcanic debris. Sand detrital modes and clast count data indicate that Waipaoa River sediments are dominated by the crushed and sheared sedimentary rocks of the East Coast allochthon, which is located in the upper portion of the catchment. Higher volcanic percentages in the Waimata and Te Arai Rivers suggest that the volcanic contribution in the Waipaoa River has likely been diluted by the great volume of sediment brought into the system from the large gullies in the catchment headwaters. Petrographic analysis of sand subfractions (very fine to very coarse) of Waipaoa River system sediment samples indicates that there is a distinct relationship between the size of the grains and their respective composition. Quartz and feldspar grains are concentrated in the finer fractions, reflecting the grain size of detrital sand liberated from Mesozoic to Cenozoic sandy source rocks. Thus, their distribution is at least in part an inherited feature related to sediment recycling within the system. Most of the sediment (gravel and sand) consists of mudstone and claystone lithic fragments. In the Waipaoa River, the sand is dominated by noncalcareous mudstone lithic fragments, some of which are smectitic. In the Waimata River, the sand grains are mainly calcareous mudstone lithic fragments. This difference in rock-fragment type reflects differences in mud rock source lithologies. Similar trends are observed in the gravel fractions of the Waipaoa River, with noted increases in calcareous gravel components in the river where it (or tributaries) traverse calcareous lithologies. These compositional differences suggest that in future studies of older alluvium and offshore sedimentary sections, it may be possible to distinguish coarse sediment derived from a purely Cenozoic source from that derived from Mesozoic rocks in the upper catchment of the Waipaoa River system, allowing us to interpret drainage evolution and denudation patterns.

Approximately 8000 lignite exploration cores, each 91 m (300 ft) deep, were used to map the gravel facies of the Upland Complex (Lafayette gravel) preserved on drainage divides in western Kentucky and Tennessee and on Crowley's Ridge in southeastern Missouri and eastern Arkansas. The Upland Complex is interpreted to be the remnant of a high-level terrace of the ancestral Mississippi-Ohio River system. The longitudinal profile of the Upland Complex and its projection on sea-level curves suggest that this alluvial deposit is early Pliocene in age (5.5–4.5 Ma). Sea level during the early Pliocene was +100 m, and the Upland Complex is interpreted to have been an ∼100-m-thick floodplain when initially deposited. Sea-level decline to −20 m at 4 Ma resulted in incision through the Pliocene floodplain, which formed the high-level terrace. Incision through the floodplain occurred in the Western and Eastern Lowlands of eastern Arkansas and their tributary valleys. The upper silt and sand facies of the terrace (∼60 m) were eroded, leaving the basal gravel-rich Upland Complex preserved on drainage divides. The New Madrid seismic zone lies beneath the Eastern Lowlands. There has been up to 100 m of denudation above the seismic zone in the past 4 m.y., and the most recent denudation occurred in the Holocene due to the confluence of the Mississippi and Ohio Rivers stepping north to Thebes Gap, Missouri. The late Wisconsin and Holocene denudation may have perturbed the local stress field and reactivated the New Madrid seismic zone.

Rivers across unglaciated portions of the Appalachian Plateaus of Tennessee and Kentucky are deeply entrenched, almost without exception. Widespread gravel deposits on upland surfaces, combined with broad straths and terraces inset beneath the highlands indicate a history of base-level stability punctuated by periods of river incision. Determining the exact timing of episodic incision historically has been difficult due to a combination of unsuitable dating methods and poorly preserved surface materials. Recently, advances in analytical techniques have allowed researchers to constrain the incision history by utilizing the hydrologic link between multilevel cave systems and regional rivers. In this study, we date clastic sediments deposited in caves associated with the Cumberland River using cosmogenic 26 Al and 10 Be, and show that they correspond to: (1) deposition of upland (Lafayette-type) gravels between ca. 5.6 Ma and ca. 3.5 Ma; (2) initial incision of regional rivers into the Highland Rim after ca. 3.5 Ma; (3) development of the Parker strath during the interval between ca. 3.5 Ma and ca. 2 Ma; (4) incision of the Parker strath at ca. 2 Ma; (5) shorter cycles of incision after ca. 1.3 Ma associated with terraces above the modern floodplain; and (6) regional aggradation at ca. 0.8 Ma. Burial ages of cave sediments record more than 5 m.y. of incision history within the unglaciated Appalachian plateaus and constrain the time needed to develop multilevel cave systems on plateau margins.