Washington Geology

WASHINGTON GEOLOGIC NEWSLETTER Volume 17 Number 3 August 1989 Washington State Department of Natural Resources Division of Geology and Earth Resources Gully erosion near Fancher Field, East Wenatchee. (See article, p. 3) IN THIS ISSUE Geologic hazards study near East Wenatchee ..... p. 3 Republic Unit at 2,000,000 ounces .................. p. 9 Geothermal exploration target area ................... p. 12 WASHINGTON Mineral Industry in 1935- Predictions and Reflections GEOLOGIC by Raymond Lasmanis NEWSLETTER Fifty-four years ago Washington was recovering from the Great Depression. There was optimism in the air. Great predictions were being made for the The Washington Geologic Newsletter is published quarterly by the Division of Geology and Earth Resources, Department of Natural future of the state's mineral industry. Resources. The newsletter is free upon request. The Division also pub lishes bulletins, information circulars, reports of investigations, geologic In 1935, a panel of experts presented their maps, and open-file reports. A list of these publications will be sent views through "A Popular Radio Story of Mineral upon request. Resources", the script of which was subsequently published by Secretary of State Ernest N. Hutchin DEPARTMENT Brian J. Boy:e son (Banker and Showalter, 1935). The panel con OF Commissioner of Public Lands sisted of: NATURAL Art Stearns RESOURCES Supervisor H. J. Gille, President of the West Coast Mineral Association; E. F. Banker, Director of the Depart ment of Conservation and Development; Milnor DMSION OF Raymond Lasmanis Roberts, Dean of the College of Mines, University of GEOLOGY AND State Geologist Washington; Joseph Daniels, Professor of Mining, EARTH RESOURCES J. Eric Schuster Asst. State Geologist University of Washington; and Henry K. Benson, Professor of Chemistry, University of Washington. The statements made about Washington's coal William M. Phillips Geologists Matthew J. Brunengo resources in this script are particularly interesting in (Olympia) Michael A. Korosec Weldon W. Rau William S. Lingley, Jr. Katherine M. Reed light of modern information and nonrenewable Robert L. (Josh) Logan Linden Rhoads resource use. At that time the U.S. Geological Sur Stephen P. Palmer Henry W. Schasse vey credited Washington with containing 64 billion Timothy J. Walsh tons of coal, and according to Gille, that was enough (Spokane) Nancy L. Joseph Keith L. Stoff el coal to last until the year 31,953 - or for 30,000 Stephanie Z. Waggoner years. Daniels covered the topic in the radio inter view, and a summary titled "Sparks" noted that Connie J. Manson Librarian Washington's reserves were three times as great as Library Technician Gwen F. Crain those of Alaska. Research Technician Arnold Bowman Although the reserves were overstated in 1935, Editor Katherine M. Reed currently coal mining is a significant industry in Cartographers Nancy A. Eberle Washington. Washington Irrigation and Develop Keith G. Ikerd ment Company operates the 24th largest coal mine m the U.S. It produces about 5 million tons of sub Jack Sareault Editorial Assistant bituminous coal annually (1988) (Schasse, 1989). Administrative Assistant Susan P. Davis The Pacific Coast Coal Co. in King County is pro Clerical Staff Naomi Hall Barb Larson ducing approximately 110,000 tons of coal a year Jim Leighton Mary Ann Shawver (1988) from its John Henry No. 1 mine (Schasse, Regulatory Clerical Staff Barbara A. Preston 1989). However, in contrast to 1935, underground mining is no longer practiced in the state. (Continued on Page 14) MAILING ADDRESSES DIVISION LOCATION (OLYMPIA) Main Office Department of Natural Resources Division of Geology and Earth Resources Mail Stop PY-12 Olympia, WA 98504 Phone: (206) 459-6372 Field Office Department of Natural Resources Division of Geology and Earth Resources Spokane County Agricultural Center .: Geology and Earth Resources: N. 222 Havana Sou nd Arctic D · 4224-6th Ave. S.E . · Spokane, WA 99202 Cente r Circ le D : _ Ro1N~six, .B'!il~in!J. <?!'~ . __ • Mall Saint Martin\ Phone: (509) 456-3255 6th Ave. S.E . Woodland Co llege DAlber tsons D Square NOTE: Publications available from Olympia address only. CITY OF LACEY Washington Geologic Newsletter, Vol. 17, No. 3 2 Geologic Hazard Investigation near East Wenatchee, Washington By Robert L. Logan Last spring the Division of Geology and Earth and flooding basements in an adjacent residential Resources responded to a landslide- and flood-re area. In order to determine the cause of the flood lated disaster affecting a four-county area in eastern and possibilities of continued problems, Canyon B Washington. In response to a presidential disaster was examined from near Fancher Field to State declaration (see related article in this issue), a Hazard Route 28 (Fig. 1). Evidence obtained during this Mitigation Survey Team was assembled. Division study supports a conclusion that a combination of geologists were asked to contribute technical input. geology, weather, and land modification was respon Although there were many individual sites in the sible for the changes in the canyon and damage on disaster area, most were affected by floods and did its alluvial fan. not require investigation of geologic features. Our Canyon B is a deeply incised V-shaped canyon study was limited to the Canyon B area located just occupied by an ephemeral stream that has cut north of East Wenatchee in Douglas County. through several lithologic units. Most of these units During the second week in March 1989, flood have been displaced by landslides that began in the waters charged with sand, mud, and rocks flowed Pliocene and have continued sporadically to the pre from Canyon B, plugging culverts, covering roads, sent (Gresens, 1983; Tabor and others, 1982). ' l \ \ \ \ \ \ t I 0 Y, mile 0 2000 feet Figure 1. Location of the Canyon B area. 3 Washington Geologic Newsletter, Vol. 17, No. 3 The oldest rock unit, Eocene sandstone of the Chumstick Formation, is exposed only in the lower reaches of the canyon. The overlying Oligocene Wenatchee Formation is composed of tuffaceous shale, siltstone, and sandstone with thin interbedded coal seams. Yakima Basalt and interbedded sand stone of Miocene age overlie the Wenatchee Forma tion. Breaching of these rocks during the Pliocene by the Columbia River caused loss of lateral support and resulted in slumping of the valley walls. Pleistocene catastrophic floods mantled these landslide materials with poorly consolidated sand and gravel bar deposits that form a terrace at about 1,400 feet elevation. The surface of the terrace has been modified in recent years. A berm several hundred feet long was Figure 2. Gully formed during March 1989 event. A recently constructed berm is to the left of the gully. constructed between Fancher Field and the adjacent Note the undermined chain-link fence on the right. property to the east (Fig. 2). The ground surface was View is toward the south. graded so that it sloped toward the berm, creating an artificial channel on the terrace. Under normal con ditions, these modifications probably would not have affected the stability of the main canyon walls. How ever, the weather conditions during February and March set the stage for disaster. A cold spell in February froze the exposed ground surface in much of eastern Washington. Be fore the ground could thaw, an insulating layer of Figure 3. Sand-covered canyon floor at the base of a minor slope failure. The terrace on the left was deposited during flood stage. The 55-gal drum provides scale. Figure 5. Confluence of a tributary and the main channel. Note the contrast between the well-armored Figure 4. A typical shallow slope failure in the main tributary channel floor and the sand-choked main channel canyon walls. channel. Bushes are about 2 feet tall. Washington Geologic Newsletter, Vol. 17, No. 3 4 Figure 6. Reactivated portion of the deep-seated failure. View is to the northwest. snow was deposited in early March. Rain fell on the snow during the second week of March. The combi nation of rain and melting snow could not penetrate the frozen ground. The resulting runoff was chan neled by the berm and the sloped surface to the canyon rim just east of Fancher Field where a new gully was formed between two older gullies. Erosion must have been rapid in the essentially cohesionless Pleistocene flood sands that make up the angle-of-re pose canyon walls in this area. Several sections of chain-link fence were undermined during the flood event, providing evidence of how much erosion has occurred. A large quantity of sand was introduced into the main canyon (Fig. 3), choking the channel, covering the normal channel cobble and boulder armor, and causing the water to rise to a level where it began to undercut the unprotected canyon walls. As a result, many small canyon-wall failures occurred (Fig. 4), adding to the sediment load of the flood stream and increasing the amount of erosion. The confluence of the main canyon stream and a tributary from the north is shown in Figure 5. Sand covers the main channel floor, but lag gravel and cobbles pave the channel of the tributary. No signifi cant failures occurred along the tributary walls, but small landslides are common in the main channel from the new gully to the canyon mouth. The tributary channel crosses a large deep seated ground failure on the north side of the main channel. Part of this landslide was reactivated during the storm event, probably by breaching and under cutting of the slide toe (Fig. 6). Movement of the Figure 7. An alluvial terrace in the canyon at the landslide into the main channel caused a temporary toe of the deep-seated failure. The present canyon impoundment of runoff (Fig. 7). Breaching of the floor is several feet below the terrace (at hammer slide toe probably caused the surge of flood water level), indicating that the landslide toe dammed the and debris that aggravated canyon wall erosion canyon and was subsequently breached.

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