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The Volcanoes of Three Sisters Region, Oregon Cascades ) Li VOLCANOES OF THETHREE SISTERS REGION, OREGON CASCADES BY HOWEL WILLIAMS UNIVERSITY OF CALIFORNIA PUBLICATIONS BULLETINOF THE DEPARTMENT OF GEOLOGICAL SCIENCES Volume 27, No. 3, pp. 37-84, plates 4-12, 4 figures in text, 1 map UNIVERSITY OF CALIFORNIA PRESS BERKELEY AND LOS ANGELES 1944 UNIvitsITY OF CATJIrORNIA PUBLICATIONS BuIIrIN OF T±LE DEPARTMENT OF GEOLOGICAL SCIENCES Ernoas (BERnELEY): G. D. LOUDEanACK, C. A. ANDERSON, C. L. CAMP, B W CRANnY, HOwiL WILLIAMS VOLUME 25, 1940-1941 Durrell, Cordell. Metamorphism in the Southern Sierra Nevada Northeast of Visalia, California. Pp. 1-118, 29 figures in text, 1 map. April 13, 1940. $1.25. Clark, Samuel G. Geology of the Covelo District, Mendocino County, California. Pp. 119-142, 7 figures in text. May 3, 1940. 25 cents. VanderHoof, V. L., and Gregory, Joseph P. A Review of the Genus Aeb&rodon. Pp. 143-164, 8 figures in text. May 9, 1940. 25 cents. Stirton, B. A. Phylogeny of North American Equidae. Pp. 165-198, 52 figures in text, 1 chart. June 14, 1940. 50 cents. Bentson, Herdis. A Systematic Study of the Fossil Gastropod Exilia. Pp. 199-238, plates 1-3, 1 table. September 24, 1940. 50 cents. Williams, Howel. Calderas and Their Origin. Pp. 239-346, 37 figures in text. April 5, 1941. $1.25. Anderson, Charles A. Volcanoes of the Medicine Lake Highland, California. Pp. 347-422, plates 4-9, 15 figures in text, 1 map. April 11, 1941. $1.00. Welles, S. P. The Mandible of a Diadeetid Cotylosaur. Pp. 423-432, 2 figures in text. April 9, 1941. 25 cents. Index. Pp. 433-438. VOLUME 26, 1941-1942 Merriam, Charles W. Fossil Turritellas from the Pacific Coast Region of North America. Pp. 1-214, plates 1-41, 19 figures in text, 1 map. March 8, 1941. $2.50. Macdonald, Gordon A. Geology of the Western Sierra Nevada between the Kings and San Joaquin Rivers, California. Pp. 215-286, plates 42-46, 7 figures in text, 1 map. October 14, 1941. $1.00. Ruth, John W. The Mollusean Genus Siphonaia of the Pacific Coast Tertiary. Pp. 287-306, plates 47-48. March 24, 1942. 25 cents. Gregory, Joseph Tracy. Pliocene Vertebrates from Big Spring Canyon, South Dakota. Pp. 307- 446, plates 49-51, 51 figures in text. July 31, 1942. $2.00. Stirton, B. A., and Goeriz, H. P. Fossil Vertebrates from the Superjacent Deposits near Knights Ferry, California. Pp. 447-472, 8 figures in text. July 21, 1942. 35 cents. Index. Pp. 473-478. VOLUME 27, 1942- VanderHoof, V. IL. A Skull of Bion latifrons frin the Pleistocene of Northern California. Pp. 1-24, plates 1 and 2, 5 figures in text. November 20, 1942. 35 cents. Richey, K. A. A Marine Invertebrate Fauna from the Orinda, California, Formation. Pp. 25-36, plate 3, 1 figure in text. April 20, 1943. 25 cents. VOLCANOES OF THE THREE SISTERS REGION, OREGON CASCADES BY HOWEL WILLIAMS UNiVERSITY OF CALIFORNIA PRESS BERKELEY AND LOS ANGELES 1944 UNIVERSITY OP CALIFORNIA PUBLICATIONS BULLETIN or DRPAaT1SurT op GsoLooicAn ScmwcEs EDITORS (BERKELEY): (1. D. LOUDERBACK, C. A. ANDERSON, C. L. CAMP, R W. CNANEY, H0wEL WILLIAMS Volume 27, No. 3, pp. 37-84, plates 4-12, 4 figures in teYt, 1 map Submitted by editors May 16, 1942 Issued June 1,1944 Price, 75 cents UNIVERSITY o CALIFORNIA PRESS BEMVELsiY AND Los ANGEnsS CALIFORNIA CAi&rnuix UNIVERSITY PRESS LONDON, ENGLAND PRINTED IN TEE UNITED STATES OF AMERICA CONTENTS PAGE Abstract 37 Introduction 37 The basement rocks 39 Age of the volcanoes Volcanoes with exposed conduits 41 North Sister 41 Little Brother 43 The Husband 43 The Wife, the Sphinx, and Burnt Top 44 Broken Top 45 The lava shield 45 The summit cone and conduit fIllings 45 Black Crater 46 Mount Washington 46 The myth of Mount Multnomah 46 The younger glaciated volcanoes 47 The Middle Sister The South Sister The original lava shield The andesite-dacite cone 49 The summit lava-scoria cones 51 Devil's Hill, Kaleetan and Kokostick buttes 51 The Todd Lake Volcano 52 Bachelor Butte EJnglaciated volcanoes 52 Tumalo Mountain 52 Trout Creek Butte 52 Palapus and Katsuk buttes Recent vulcanism 53 The LeConte Crater and flows Cayuse cone and flows 54 Sims Butte and related flows 54 Scoria cones and flows north of the North Sister 55 The Belknap craters and flows 56 Belknap Crater 56 Little Belknap 57 Pumice deposits 57 Obsidian flows and domes 58 Rock Mesa 58 The Newberry and Devil's Hill obsidians 58 Summary of the volcanic history 59 Petrography 59 The older basalts and basaltic andesites 59 The plugs of the older volcanoes 61 Recent basalts and basaltic andesites 61 Andesites 62 Dacites 63 Plates 65 Map 84 VOLCANOES OF THE THREE SISTERS REGION, OREGON CASCADES BY HOWEL WILLIAMS ABSTRACT During Pliocene time a cluster of basaltic and basaltic andesite shield volcanoes was built in the Three Sisters region. Included in this cluster are the North Sister, Little Brother, Husband, Wife, Sphinx and Broken Top, the radial dikes and conduit fillings of which have been laid bare by glacial erosion. The view that this arcuate line of peaks marks the rim of a caldera formed by decapitation of an enormous central volcano, Mount Multnomah, is shown to be erroneous. During the Pleistocene, andesites and dacites were erupted, principally by the Middle and South Sisters, while new basaltic cones were growing elsewhere. During Recent time, still other cones of basaltic lava and scoria were formed and vast flows were poured from some of them, notably from the Belknap Craters near McKenzie Pass, while showers of pumice and viscous domes of obsidian were erupted by neighboring vents. Some of these eruptions ended only a few centuries ago; nowhere in the High Cascades has there been more volcanic aetivity within the last millennium. Taken as a whole, the magmatic history closely resembles that of the Crater Lake region and the post-Miocene activity of other parts of the Cascade Range farther south. INTRODUCTION THE CASCADE RANGE is divisible longitudinally into two belts, the Western and the High Cascades (fig. 1). The former consists of gently folded volcanic rocks that range in age from Eocene to upper Miocene. The topography in this region is mature and bears no relation to the original volcanic forms. The High Cascades, on the other hand, consist of Pliocene and younger volcanic rocks, almost completely unde- formed. The topography here is constructional, and the forms of the individual volcanoes, even where modified by glaciation, are easy to recognize. Throughout their length in Oregon, the High Cascades are crowned by huge snow- and ice-capped cones. For magnificence of glacial scenery, for wealth of recent lavas, and for graphic examples of dissected volcanoes no part of this range surpasses the area embracing the Sisters and McKenzie Pass. Seventeen glaciers still survive on the higher peaks; moraine-dammed lakes and ice-cut tarns occur in profusion around their feet; barren sheets of basalt, no more than a few centuries old, cover almost 100 square miles; youthful cinder cones and fresh fields of blocky obsidian add variety to the landscape; and the older volcanoes are so deeply denuded that their central conduits and radial dikes are magnificently displayed. When, in 1924, lodge1 made the first geological survey of this inviting country, he concluded that the Three Sisters rest upon the worn remnants of a vastly larger volcano. To this vanished peak, he gave the name Mount Multnomah. He supposed that at the close of the Miocene or at the very beginning of the Pliocene period, the top of the ancient mountain was destroyed by colossal explosions and that a caldera between eight and nine miles wide was formed in its place. Giving imagination sway, he pictured a lake within the ealdera, encircled by cliffs from 3,000-4,000 feet in height. When volcanic activity was resumed, the Middle and South Sisters were built within the great depression. Hodge's startling hypothesis gained wide credence. Many who saw the arc of peaks that runs from Broken Top through the Devil's Hill, the Wife and Sphinx, 1 lodge, E. T., Mount Multnomah, Ancient Ancestor of the Three Sisters, Univ. of Oregon Pubi., vol. 2, no. 10, 1925. A N A 0 A S I-I I N 0 -tt. Baiev T 0 0 10750 -Glacley IL -4Io436 ®SEATTLE _ Rai,/iey 1440: /. HeItur 9671 -'7)..j23O7 POR.TLAN o - 41tHaod j' _J1253 SALEMJ'0111. o L Bu. / 7243 ?-.-- TJeicram r\ /0495 GEN r /035* BEND ,1 -412Ideiz L11 7750 Q:'1J;;0111pk. - L;-7-./-' 1750 1 ,ThieIfw.. LaL 9/7S \DFORDMATHftcouj%In 9497 0 0 N çcMODOC N E V. - . \ 'CZ "LAVA \ BEDS \ -41tfAaria ?' <rI/1161 RED DING ' RED BLUFF Fig. 1. Map of the Oascade Range showing loeation of the Three Sisters. Williams: Volcanoes of the Three $isters Region 39 the Husband, Little Brother and North Sister, agreed that these might well mark an old caldera rim. Noting the long slopes that lead outward from the arc of peaks, it was easy to imagine them continuing inward and upward to an enormous, central cone. Study of many calderas in the circum-Pacific region had led the present writer to the view that large volcanic depressions are formed principally by collapse, that explosions by themselves seldom produce depressions more than a mile in width.' A survey of the ejecta blown from Mount Mazama had likewise led to the conclusion that Crater Lake was caused, nOt by explosive removal of the ancient peak, but by engulfment. One of the prime objects of the present reconnaissance was therefore to find out whether or not such a peak as Mount Multnomah ever existed, and, if it did, to discover how it was demolished.
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