Ice and water on Newberry Volcano, central Oregon

Abstract

Newberry Volcano in central Oregon is dry over much of its vast area, except for the lakes in the caldera and the single creek that drains them. Despite the lack of obvious glacial striations and well-formed glacial moraines, evidence indicates that Newberry was glaciated. Meter-sized foreign blocks, commonly with smoothed shapes, are found on cinder cones as far as 7 km from the caldera rim. These cones also show evidence of shaping by fl owing ice. In addition, multiple dry channels likely cut by glacial meltwater are common features of the eastern and western fl anks of the volcano. On the older eastern fl ank of the volcano, a complex depositional and erosional history is recorded by lava fl ows, some of which fl owed down channels, and interbedded sediments of probable glacial origin. Postglacial lava fl ows have subsequently fi lled some of the channels cut into the sediments. The evidence suggests that Newberry Volcano has been subjected to multiple glaciations. *jdnolan@usgs.gov bjensen@bendnet.com Donnelly-Nolan, J.M., and Jensen, R.A., 2009, Ice and water on Newberry Volcano, central Oregon, in O’Connor, J.E., Dorsey, R.J., and Madin, I.P., eds., Volcanoes to Vineyards: Geologic Field Trips through the Dynamic Landscape of the Pacifi c Northwest: Geological Society of America Field Guide 15, p. 1–10, doi: 10.1130/2009.fl d015(04). For permission to copy, contact editing@geosociety.org. ©2009 The Geological Society of America. All rights reserved. INTRODUCTION Nestled within the scenic 45 km2 Newberry caldera at the top of Newberry Volcano (Fig. 1) are two beautiful lakes— Paulina Lake and East Lake—that are popular destinations for fi shing, boating, swimming, and camping. Paulina Lake covers ~6 km2 whereas the smaller East Lake covers only ~4 km2. East Lake, which has no surface outlet, is ~15 m higher than Paulina Lake, which has a surface elevation of 1930 m. The latter drains across a small dam sited on the low western caldera rim into Paulina Creek, and the creek is augmented just below the dam by a small cold spring. No surface springs or creeks feed either lake. Both are fed by snowmelt and by groundwater, including thermal water. Paulina Creek fl ows at a rate of ~0.5 m3/sec (Morgan et al., 1997) west for ~15 km to Paulina Prairie at the edge of Newberry Volcano. Here the fl ow is considerably diminished because of losses into permeable lavas of Newberry. The image of Newberry Volcano (Figs. 1 and 2) as host to lakes and a rushing stream that cascades over several waterfalls on its way to the Deschutes River belies the truth. Aside from the caldera and the immediate vicinity of Paulina Creek, the volcano is a dry, dusty place for most of the year. Winter snow and summer thunderstorms soak into the permeable volcanic rocks and add to groundwater. Runoff of surface water is rarely seen except on hard surfaces such as roads, even during the heaviest thundershowers. Annual total precipitation ranges from ~25 cm on the lower fl anks to >75 cm over the highest part (http://nationalatlas.gov, map of Oregon precipitation), but springs and streams are absent on the fl anks and distal lava fl ows of this nearly 3000 km2 volcano. Dry channels, however, 2 Donnelly-Nolan and Jensen fl d015-04 1st pgs page 2