ABSTRACT With waterfalls and the deepest gorge in Pennsylvania, Ohiopyle State Park provides opportunities to observe a variety of habitats and three-dimensional (3-D) exposures of the Pennsylvanian sandstone most responsible for shaping Laurel Highlands landscapes. Evidence for the relationship between bedrock, ancient climates, and the landscape can be observed at some of the most scenic natural features of the park: Baughman Rock Overlook, Cucumber Falls, Ohiopyle Falls, Meadow Run Waterslide and Cascades, and Youghiogheny River Entrance Rapid. Channel azimuths and lateral variations in thickness of upper Pottsville fluvial/deltaic sandstone suggest that deposition was influenced by deformation of this part of the Allegheny Plateau during the Alleghanian orogeny. Geologic features of Pottsville sandstone outcrops include a 10-m- (~33-ft-) long Lepidodendron fossil and a 3-D exposure of a meter-high Pennsylvanian subaqueous sand dune and scour pit. Cosmogenic age dating has indicated very slow erosion of hard sandstone in an upland location at Turtlehead Rock and informed estimation of Pleistocene/Holocene waterfall retreat rates of Ohiopyle and Cucumber Falls. Bedrock exposures supporting scour habitats along the Youghiogheny River occur only in a limited area of Youghiogheny Gorge where knickpoint migration and bedrock erosion were relatively recent. Geologic factors, including locations of major tributaries, development of bars that constrict river flow, and proximity of Homewood sandstone outcrops as sources of boulder obstacles in the river, contributed to the class, location, and nature of whitewater rapids in the lower Youghiogheny River.

ABSTRACT Iceland is a young, dynamic, volcanic island with a unique tectonomagmatic setting at the intersection of the Mid-Atlantic Ridge and a mantle hotspot. The combination of this tectonomagmatic setting, a history of glaciation, and the sparse vegetation of a subarctic maritime climate means that Iceland has both intriguing geology and outstanding exposures of this geology. This field trip guide contains an introduction to the geology of Iceland and an itinerary for a 10-day journey around the island. The itinerary consists of 55 stops and 15 optional stops. These stops include exposure to representative examples of most phenomena typical of the island’s geology and all of the major tectonic elements of Iceland. The primary focus of this guide is on volcanic and tectonic features, but topics such as glaciation, geothermal energy, geomorphology, paleontology, soil loss, and geotourism are also addressed.

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 Waterfalls have long attracted the attention of travellers, some of whom were writers and artists who have left us a cultural legacy of their observations and interpretations. Likewise, geologists have studied and recorded these landscape features since the infancy of their science. An examination of travellers’ experiences of waterfalls since the emergence of Romanticism in eighteenth-century Europe reveals a variety of responses, both utilitarian and aesthetic. Seen as valuable sources of renewable energy, impediments to navigation, beautiful, sublime or picturesque natural wonders and resources for tourism, waterfalls continue to appeal to the Romantic traveller and the pleasure-seeking tourist. Increasingly, waterfalls are being threatened by schemes to exploit them, especially for power generation or intensive tourism development. In many parts of the world, this presents a serious challenge to those responsible for the management of this often spectacular aspect of geodiversity. This paper explores these various themes which are contextualized within the historical and cultural framework of Romanticism.

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 San Francisco Volcanic Field, located in northeastern Arizona, is host to over 600 volcanoes. These volcanoes began erupting approximately 6 million years ago in the western portion of the field and through time, the locus of activity has migrated eastward. Eruptive products range from basalt to rhyolite, with basalt dominant. Pleistocene vents include Merriam Crater and two associated cinder cones as well as The Sproul, a spatter rampart. One, or several, of these vents produced the Grand Falls flow which spilled over into the Little Colorado River gorge and flowed both up and downstream. Lava filled the canyon producing a dam and continued to flow ~ 1 km beyond the eastern rim. This changed the course of the river creating the waterfall at Grand Falls. Quaternary volcanism began as a fissure eruption that culminated with the building of Sunset Crater cinder cone. The eruption, which produced a blanket of tephra and two lava flows, was most certainly witnessed by the ancestors of the Pueblo Indians and had a dramatic impact on their lives. The eruption may have caused a shift in population to places such as Wupatki, 30 km to the north, where farming in the arid climate may have been temporarily enhanced by a thin layer of ash that acted as a water-retaining mulch. Melts that produced these dominantly basaltic cinder cones were derived by variable amounts of partial melting of an oceanic island basalt–like mantle source that underwent differing degrees of contamination from the lower crust. Subsequent fractional crystallization of olivine ° clinopyroxene further modified these melts. Discrete packets of these melts ascended rapidly to produce short-lived volcanic events in the eastern San Francisco Volcanic Field. The purpose of this field trip is to examine these young cinder cones and their eruptive products in an effort to understand the origin of the eruptions as well as the effects they had on the physiography and native inhabitants of the area.