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Geologic Map of the Katmai Volcanic Cluster, Katmai National Park, Alaska by Wes Hildreth and Judy Fierstein

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Geologic Map of the Katmai Volcanic Cluster, Katmai National Park, Alaska by Wes Hildreth and Judy Fierstein Geologic Map of the Katmai Volcanic Cluster, Katmai National Park, Alaska By Wes Hildreth and Judy Fierstein Aerial view along the main volcanic chain from the caldera lake of Mount Katmai across the craggy peaks of Trident Volcano to snow-clad Mount Mageik, a distance of about 20 km. Sea fog from Shelikof Strait invades Katmai Pass (between Trident and Mageik) and fingers into the Valley of Ten Thousand Smokes, the pale-tan ignimbrite-filled floor that lies at right center. Katmai caldera formed on June 6-7, 1912, in response to withdrawal of magma that vented at Novarupta, 10 km west, at the head of the Valley of Ten Thousand Smokes. Caldera walls rise 250-800 m above the lake, which is 250 m deep and still filling. View toward southwest from helicopter. Pamphlet to accompany Geologic Investigations Series I–2778 2003 U.S. Department of the Interior U.S. Geological Survey CONTENTS INTRODUCTION ................................................................................................................................................................. 1 Physiography and Access ....................................................................................................................................... 1 Previous Work ........................................................................................................................................................ 1 Methods .................................................................................................................................................................. 4 GEOLOGIC SETTING ......................................................................................................................................................... 5 Basement Rocks ..................................................................................................................................................... 5 Convergent Margin ................................................................................................................................................. 5 THE QUATERNARY VOLCANOES .................................................................................................................................. 5 Mount Griggs .......................................................................................................................................................... 5 Alagogshak Volcano ............................................................................................................................................... 6 Mount Martin .......................................................................................................................................................... 6 Mount Mageik ........................................................................................................................................................ 7 Trident Volcano ....................................................................................................................................................... 7 Mount Katmai ......................................................................................................................................................... 10 Novarupta ............................................................................................................................................................... 11 Snowy Mountain .................................................................................................................................................... 11 Rainbow River Cone .............................................................................................................................................. 11 Clustered Stratovolcanoes ...................................................................................................................................... 12 Influence of ice ....................................................................................................................................................... 12 ERUPTIVE HISTORY OF THE KATMAI CLUSTER ....................................................................................................... 13 The Stratovolcanoes and Lava Domes ................................................................................................................... 13 Recent Eruptions .................................................................................................................................................... 14 The 1912 Eruption .................................................................................................................................................. 15 COMPOSITIONS OF THE ERUPTIVE PRODUCTS ........................................................................................................ 18 VOLCANO HAZARDS ........................................................................................................................................................ 19 ACKNOWLEDGMENTS ..................................................................................................................................................... 22 DESCRIPTION OF MAP UNITS ........................................................................................................................................ 22 REFERENCES CITED ......................................................................................................................................................... 38 Table 1. Data for Katmai Cluster Volcanoes ........................................................................................................................ 3 Figure 1. Regional Location Map ........................................................................................................................................ 2 Figure 2. Eruptive sequence of 1912 ................................................................................................................................... 17 Figure 3. Compositions of eruptive products ................................................................................................................. 20-21 i INTRODUCTION Thousand Smokes (Hildreth, 1987; Hildreth and Fierstein, 2000). The frontal volcanoes of this arc segment from Devils The Katmai volcanic cluster on the Alaska Peninsula Desk to Alagogshak were constructed along the pre-existing (fig. 1) was first brought to national and international atten­ rangecrest (the Pacific-Bristol Bay drainage divide), where tion by the great eruption of June 1912. Although many wil­ the rugged prevolcanic basement typically reaches elevations derness travellers and one geological party (Spurr, 1900) had of 1,200–1,600 m. As the volcanic summits reach 1,830– previously crossed remote Katmai Pass on foot, the National 2,290 m and lie in a region of high precipitation, all the cen­ Geographic Society expeditions of 1915-19 first mapped and ters are heavily ice covered, as (to a lesser degree) is reconnoitered the volcanic terrain surrounding the pass in 2,330-m-high Mount Griggs northwest of the frontal axis. the course of investigating the effects of the 1912 eruption The Katmai cluster lies entirely within the wilderness (Griggs, 1922; Higbie, 1975). The explosive ejection of rhy­ of Katmai National Park, 450 km southwest of Anchorage olitic, dacitic, and andesitic magma at Novarupta (fig. 1) over and 170 km west of Kodiak (fig. 1). The only convenient an interval of about 60 hr on June 6-8, 1912, (Martin, 1913; access is by boat or amphibious aircraft from King Salmon Curtis, 1968; Hildreth, 1983) was the world’s most volumi­ to Brooks Camp on Naknek Lake. Scheduled commercial nous 20th century eruption. At least 17 km3 of fall deposits air service is available during summer months, and scenic and 11±3 km3 of ash-flow tuff (ignimbrite) were produced, flight tours of the volcanoes can be arranged in good weather representing a magma volume of about 13 km3 (Fierstein at both places. A daily commercial shuttle bus or van traverses and Hildreth, 1992). This volume is larger than that erupted a 37-km-long dirt road from Brooks Camp to the Overlook by Krakatau (Indonesia) in 1883 and is known to have been Cabin, a visitor center perched on a scenic knoll near the exceeded by only four eruptions in the last 1,000 years terminus of the ash-flow sheet in the Valley of Ten Thousand (Simkin and Siebert, 1994). Syneruptive caldera collapse at Smokes. The distal part of the sheet can be reached in an Mount Katmai (Hildreth, 1991), 10 km east of the eruption hour’s walk by steep trail from the Overlook Cabin, but any­ site, and displacements elsewhere in the magmatic plumb­ thing more than a brief visit demands camping expertise and ing system generated 14 earthquakes in the magnitude range survival equipment. We have encountered moose, caribou, Ms 6 to 7 (extraordinarily energetic for volcanic seismicity) foxes, wolves, wolverines, and many brown bears, as well and as many as 100 greater than Ms 5 (Abe, 1992; Hildreth as various smaller critters that would eat your lunch. Reach­ and Fierstein, 2000). ing Novarupta requires a day-long backpack trip, each way. Within 15 km of the 1912 vent at Novarupta, five The surrounding ice-clad stratovolcanoes should not be andesite-dacite stratovolcanoes have erupted during the climbed without mountaineering skills and equipment. High Holocene and remain fumarolically active today: Mount winds, frequent rain and drizzle, brown bears, icy stream
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