First posted August 16, 2017 For additional information, contact: Volcano Science Center - Menlo ParkU.S. Geological Survey345 Middlefield Road, MS 910Menlo Park, CA 94025 The Cascade Range in central Oregon has been shaped by tectonics, volcanism, and hydrology, as well as geomorphic forces that include glaciations. As a result of the rich interplay between these forces, mafic volcanism here can have surprising manifestations, which include relatively large tephra footprints and extensive lava flows, as well as water shortages, transportation and agricultural disruption, and forest fires. Although the focus of this multidisciplinary field trip will be on mafic volcanism, we will also look at the hydrology, geomorphology, and ecology of the area, and we will examine how these elements both influence and are influenced by mafic volcanism. We will see mafic volcanic rocks at the Sand Mountain volcanic field and in the Santiam Pass area, at McKenzie Pass, and in the southern Bend region. In addition, this field trip will occur during a total solar eclipse, the first one visible in the United States in more than 25 years (and the first seen in the conterminous United States in more than 37 years).The Cascade Range is the result of subduction of the Juan de Fuca plate underneath the North American plate. This north-south-trending volcanic mountain range is immediately downwind of the Pacific Ocean, a huge source of moisture. As moisture is blown eastward from the Pacific on prevailing winds, it encounters the Cascade Range in Oregon, and the resulting orographic lift and corresponding rain shadow is one of the strongest precipitation gradients in the conterminous United States. We will see how the products of the volcanoes in the central Oregon Cascades have had a profound influence on groundwater flow and, thus, on the distribution of Pacific moisture. We will also see the influence that mafic volcanism has had on landscape evolution, vegetation development, and general hydrology.
Silica-undersaturated magmas intruded stable continental crust in southern Texas throughout Late Cretaceous time, forming at least 200 small volcanic centers and intrusive bodies in a shallow, epicontinental sea. Rock types, in order of decreasing abundance in outcrop, are melilite-olivine nephelinite, olivine nephelinite, alkali basalt, phonolite, and nepheline basanite. Melilite-olivine nephelinite, olivine nephelinite, and nepheline basanite contain xenoliths of spinel lherzolite, dunite, and harzburgite.
Volcanic provinces are among the most active but least well understood landscapes on Earth. Here, we show that the central Cascade arc, USA, exhibits systematic spatial covariation of topography and hydrology that are linked to aging volcanic bedrock, suggesting systematic controls on landscape evolution. At the Cascade crest, a locus of Quaternary volcanism, water circulates deeply through the upper [Formula: see text]1 km of crust but transitions to shallow and dominantly horizontal flow as rocks age away from the arc front. We argue that this spatial pattern reflects a temporal state shift in the deep Critical Zone. Chemical weathering at depth, surface particulate deposition, and tectonic forcing drive landscapes away from an initial state with minimal topographic dissection, large vertical hydraulic conductivity, abundant lakes, and muted hydrographs toward a state of deep fluvial dissection, small vertical hydraulic conductivity, few lakes, and flashy hydrographs. This state shift has major implications for regional water resources. Drill hole temperature profiles imply at least [Formula: see text] km[Formula: see text] of active groundwater currently stored at the Cascade Range crest, with discharge variability a strong function of bedrock age. Deeply circulating groundwater also impacts volcanism, and Holocene High Cascades eruptions reflect explosive magma-water interactions that increase regional volcanic hazard potential. We propose that a Critical Zone state shift drives volcanic landscape evolution in wet climates and represents a framework for understanding interconnected solid earth dynamics and climate in these terrains.
Abstract Newberry Volcano is located in central Oregon at the intersection of the Cascade Range and the High Lava Plains. Its lavas range in age from ca. 0.5 Ma to late Holocene. Erupted products range in composition from basalt through rhyolite and cover ~3000 km2. The most recent caldera-forming eruption occurred ~80,000 years ago. This trip will highlight a revised understanding of the volcano's history based on new detailed geologic work. Stops will also focus on evidence for ice and flooding on the volcano, as well as new studies of Holocene mafic eruptions. Newberry is one of the most accessible U.S. volcanoes, and this trip will visit a range of lava types and compositions including tholeiitic and calc-alkaline basalt flows, cinder cones, and rhyolitic domes and tuffs. Stops will include early distal basalts as well as the youngest intracaldera obsidian flow.
Abstract The northwest rift zone (NWRZ) eruption took place at Newberry Volcano ~7000 years ago after the volcano was mantled by tephra from the catastrophic eruption that destroyed Mount Mazama and produced the Crater Lake caldera. The NWRZ eruption produced multiple lava flows from a variety of vents including cinder cones, spatter vents, and fissures, possibly in more than one episode. Eruptive behaviors ranged from energetic Strombolian, which produced significant tephra plumes, to low-energy Hawaiian-style. This paper summarizes and in part reinterprets what is known about the eruption and presents information from new and ongoing studies. Total distance spanned by the eruption is 32 km north-south. The northernmost flow of the NWRZ blocked the Deschutes River upstream from the city of Bend, Oregon, and changed the course of the river. Renewed mafic activity in the region, particularly eruptions such as the NWRZ with tephra plumes and multiple lava flows from many vents, would have significant impacts for the residents of Bend and other central Oregon communities.
