ABSTRACT About 17,000 yr ago, Glacial Lake Maumee breached the Fort Wayne Moraine, sending an unimaginably large torrent of meltwater down the upper Wabash River Valley (UWRV). The Maumee Megaflood (MM) may have lasted only a few weeks, but it scoured out a deep trough along the main stem of the river, radically lowering regional base level in what amounts to a geological instant and imposing a strong disequilibrium on a landscape that continues to experience major geomorphic, environmental, and ecological adjustments. In Huntington and Wabash Counties, the central part of the trough is engorged in resistant, Late Silurian reef-associated and inter-reef rocks, producing the largest natural bedrock exposure in heavily glaciated northern Indiana. Unlike the immature, deranged drainage pattern that characterizes most of the glaciated region, streams adjacent to the UWRV form well-integrated drainage networks that exhibit features and processes more typical of high-relief bedrock areas, such as steep fall zones with prominent, lithologically controlled knickpoints, canyons, large terraces, falls and cascades, and a variety of bluff and hillside morphologies and associated groundwater phenomena. The exceptional exposures and diverse landscape of this region have attracted well over a century of interest from geomorphologists and glacial geologists, sedimentologists, stratigraphers, and paleontologists, as well as hydrogeologists, anthropologists, ecologists, and geoscience educators. Among other firsts, the organic origin of fossil reefs in the southern Great Lakes was definitively established in the UWRV, as was the occurrence of convulsive meltwater outbursts during deglaciation of the Laurentide Ice Sheet; likewise, the first direct Mississippi River–Great Lakes connection was also established here by early voyageurs. Today, the region is a popular destination for both nature tourism and history buffs, due in no small part to the burgeoning number of geologically inspired natural areas and historical sites. This field trip traces the MM from its outlet at Fort Wayne, through the bedrock gorge of the upper Wabash River, to the confluence with the late Tertiary Teays Bedrock Valley, with major emphasis on how the depositional framework and diagenetic history of the Late Silurian reef archipelago continue to reverberate in the modern geomorphic response of the valley to Pleistocene events. The first three stops focus on the Wabash-Erie Channel, which acted as the principal outlet of Glacial Lake Maumee and whose underlying geologic characteristics controlled the overall incision history of the MM. Several stops in the Wabash bedrock gorge and Salamonie Narrows will examine the handiwork of this flood, which created the spectacular klintar, or pinnacle-like reefs, of the UWRV, within a landscape that early geomorphologists likened to the scablands of eastern Washington. There, we will see world-class exposures of the fossilized Late Silurian reefs and how their organic framework and diagenesis are controlling the ongoing adjustment of the UWRV landscape and its streams to the convulsive changes imposed by the MM. Stop 9 will showcase the elusive Teays Bedrock Valley and its complex pre-Wisconsin fill, where it converges with the modern river and has been partially exhumed by a major tributary, and offers a study in contrasts between the bedrock-controlled landscapes of earlier stops and an equally steep one excavated entirely into unconsolidated deposits. After a brief stop at the iconic Seven Pillars landmark, the trip concludes at the spectacular Pipe Creek Jr. Quarry, which features several km of tall exposures through the Late Silurian carbonate complex, a late Neogene sinkhole deposit, and the overlying Pleistocene section.

Abstract Rare jökulhlaup events, also known as subglacial lake outburst flood events, have been observed at the Law Dome ice margin and provide an insight into the physical characteristics of subglacial meltwater and drainage. The subglacial topography based on data from the BEDMAP2 and ICECAP projects, together with subsurface transects of the ice margin obtained using ground-penetrating radar, reveal several lakes and lake-like depressions and the drainage pathways of two jökulhlaup events. Oxygen isotope typing of the meltwater during the most recent (2014) jökulhlaup event, combined with ice margin stratigraphy, enable the identification of ice tunnel melt pathways that exploit the 30–90° dipping basal ice layering. The presence of subglacial meltwater beneath Law Dome during the Holocene to Glacial periods is confirmed by the dendritic drainage pattern in the subglacial morphology and extensive layers of basal regelation ice and subglacial carbonate precipitate deposits found within the Løken Moraines sediments. These subglacial carbonates, including ooid layers, formed from the mixing of glacial meltwater and seawater at 72 ka BP. The combined evidence indicates that the ocean discharge of subglacial meltwater may be variable and/or is periodically blocked by basal freezing events near the ice sheet terminus.

ABSTRACT The rich Quaternary history of the Pacific Northwest showcases the important linkages between multiple geologic processes that have shaped its sedimentology and geomorphology. This field trip in eastern Washington explores the evolution of landforms that developed within the Palouse and the Channeled Scabland—geomorphically distinctive areas that were indirectly and directly influenced by multiple Quaternary glacial outburst megafloods. These floods produced expansive fine-grained sediments that were subsequently remobilized by the wind to generate sand dunes, sand sheets, and the thick loess of the Palouse. Landforms and deposits that date from the Last Glacial Maximum (LGM) include dramatically eroded scab-land features, coarse-to fine-grained flood slackwater deposits, sand dunes, loess, and paleosols. Sedimentary, paleopedologic, and geomorphic evidence for similar magnitude glacial outburst megafloods and loess accumulation that are related to the penultimate glaciation, during oxygen isotope stage 4, is recorded in several loess outcrops. This field trip traces the windblown sediments from source to sink and particularly focuses on Eureka Flat—the engine of the Palouse loess—and well-studied sections of thick loess farther downwind. A rich paleoclimate record is emerging from the loess stratigraphy and paleosols based on luminescence ages, tephrochronology, and paleoecologic analyses.

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 This one-day field trip of geologic and historical significance goes from Washtucna, Washington, through Palouse Falls State Park, Lyons Ferry State Park, and Starbuck, and ends in the Tucannon River valley. At Palouse Falls, it is readily apparent why Native Americans crafted stories about the origins of this spectacular area and why geologic debates regarding the role of Pleistocene glacial Lake Missoula floods during the formation of this natural wonderland have been centered here. This field trip focuses on structural geology and the Palouse Falls fracture zone, Columbia River Basalt Group stratigraphy at the falls, and subsequent erosion by glacial outburst floods. Discussion of the falls will include human history and the formation of Palouse Falls State Park. The main stop at Palouse Falls will explore the stratigraphy of the Columbia River Basalt Group, Vantage Member, loess islands, fracture zones, and human history dating back at least 12,000 yr. Driving south through Lyons Ferry State Park and the Tucannon Valley, we will discuss topics ranging from the Palouse Indians to sheep herding and from clastic dikes to terracettes.

Abstract The Middle Fork Nooksack River drains the southwestern slopes of the active Mount Baker stratovolcano in northwest Washington State. The river enters Bellingham Bay at a growing delta 98 km to the west. Various types of debris flows have descended the river, generated by volcano collapse or eruption (lahars), glacial outburst floods, and moraine landslides. Initial deposition of sediment during debris flows occurs on the order of minutes to a few hours. Long-lasting, down-valley transport of sediment, all the way to the delta, occurs over a period of decades, and affects fish habitat, flood risk, gravel mining, and drinking water. Holocene lahars and large debris flows (>10 6 m 3 ) have left recognizable deposits in the Middle Fork Nooksack valley. A debris flow in 2013 resulting from a landslide in a Little Ice Age moraine had an estimated volume of 100,000 m 3 , yet affected turbidity for the entire length of the river, and produced a slug of sediment that is currently being reworked and remobilized in the river system. Deposits of smaller-volume debris flows, deposited as terraces in the upper valley, may be entirely eroded within a few years. Consequently, the geologic record of small debris flows such as those that occurred in 2013 is probably very fragmentary. Small debris flows may still have significant impacts on hydrology, biology, and human uses of rivers downstream. Impacts include the addition of waves of fine sediment to stream loads, scouring or burying salmon-spawning gravels, forcing unplanned and sudden closure of municipal water intakes, damaging or destroying trail crossings, extending river deltas into estuaries, and adding to silting of harbors near river mouths.

Abstract As the late Pleistocene Cordilleran Ice Sheet (CIS) retreated from the southern Puget Lowland and thinned rapidly, marine waters invaded the central and northern lowland, floating the residual ice and causing wholesale collapse of the CIS from southern Whidbey Island to southern British Columbia. Massive, poorly sorted Everson glaciomarine drift was deposited contemporaneously over the entire central and northern lowland. More than 160 14 C dates show that the Everson interval began 12,500 14 C yr B.P. and ended 11,700 14 C yr B.P. Numerous marine strandlines record the drop in relative sea level in the Fraser Lowland from ~180 m (600 ft) at the end of the Everson interval to near present sea level. Following emergence of the Fraser Lowland, a lobe of the CIS advanced from the Fraser Canyon near Sumas to Bellingham during the Sumas Stade. As the ice retreated, at least eight end moraines were built successively across the lowland, each marking a position of ice advance or stillstand that records late Pleistocene climatic fluctuations. About 40 new 14 C dates indicate that the ages of these moraines span the Inter-Allerød–Younger Dryas intervals between 11,700 and 10,000 14 C yr B.P. The 14 C chronology allows correlation of the Sumas moraines with moraines in the Cascade Range, Rocky Mountains, Canada, Scandinavia, the European Alps, New Zealand, South America, and elsewhere. Late in the retreat of the ice, large outburst floods from an ice-dammed lake in British Columbia swept across the Sumas outwash plain, resulting in fluted topography and giant ripples on dune forms.

Abstract This field guide examines Quaternary volcanism in the Canadian Cascade arc informally known as the Garibaldi Volcanic Belt. During the first day, the trip proceeds along the Sea-to-Sky Highway corridor from Vancouver to Pemberton and focuses on Quaternary glaciovolcanic deposits and lavas. Interactions between volcanoes and ice in the Garibaldi Volcanic Belt have been common during the past two million years, which has resulted in a diverse array of landforms, including subglacial domes, tuyas, impounded lava masses, and sinuous lavas that exploited within-ice drainage systems. On Days 2 and 3, the trip heads northwest of Pemberton, British Columbia, along logging roads to see deposits from the 2360 yr B.P. eruption of the Mount Meager volcanic complex. The eruption began Plinian-style, generating pyroclastic fall and density current deposits (Day 2) and ended with the production of welded and nonwelded block and ash flows by explosive (Vulcanian) collapse of a lava (Day 3). The guide will examine the deposits of the temporary lake impounded by a block and ash flow deposit dam, and the evidence of the catastrophic failure of the dam and the generation of a huge outburst flood and lahar. Many of the traits of the deposits seen on this three-day trip are a reflection of both the style of eruption and the nature of the surrounding landscape. In this regard, the trip provides a spectacular window into the nature and hazards of effusive and explosive volcanism occurring in mountainous terrains and the role of water and ice.

Analysis of geologic materials at the microscale—where we use the term “microscale” to refer to features resolved approximately by a hand lens—has proven to be a powerful strategy to maximize the information gleaned from limited samples, such as on Mars. However, discrimination between processes that leave behind similar traces requires enlightened comparisons to well-characterized analogs. We characterized and imaged several terrestrial analogs of materials produced by volcanic, hydrovolcanic, or cryovolcanic Martian processes at the hand lens scale, and then we produced a convenient tool for the community to access those data for comparisons. We report on the preparation of this Mars-focused image atlas (the Mars Analog Handlens-Scale Image Database), using as an example analog studies of particles deposited by the 1996 Skeiđarársandur jökulhlaup (a jökulhlaup is a subglacially generated outwash flood resulting in a sandur, or sheet of outwash sands and gravel). We imaged unconsolidated sediment particles in situ at about hand lens scale and documented their characteristics at six sites along the sandur. Average particle size and number of angular, very angular, and subangular particles decreased with distance from the source; the average sphericity of particles increased slightly; and the range of sphericity values present narrowed with distance. If observed in a region on Mars, this combination of characteristics would be one indicator that subglacially generated outwash flooding was the process responsible for deposition of sediment. The Mars Analog Handlens-Scale Image Database is searchable and can be found on the Geosciences Node of the Planetary Data System at http://an.rsl.wustl.edu/marsanalog/ .