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North and northeast wall of Katmai caldera viewed from southeast rim. 27) was recognized by Griggs (1922) to be a secondary pumiceous diamict emplaced at low temperature atop the stratified dacite fallout that concluded the plinian eruption, but several subsequent observers interpreted it as a hot pyroclastic-flow deposit, which it resembles (fig. 3). The mountain is located in Kodiak Island Borough, very close to its border with Lake and Peninsula Borough. Upper third of black and red wall at left is rhyodacite lava and breccia (unit krs), uppermost part of which banks against and overlies zoned scoria-fall deposit; beneath rhyodacites, middle third of wall is stack of dacite lava flows, one of which gave a 40Ar/39Ar plateau age of 81 7 ka. Lower sections of the Knife Creek Glaciers are a badlands of ice covered with as much as six feet of ash and pumice. At lower left, two promontories expose a west-dipping stack of altered lava flows and breccias that appears to be continuous with the northwest wall sequence; exposed for 100 m above lake level, the altered stack unconformably underlies the main dacite lava sequence that dominates the southwest wall (Fig. Many earthquakes were said to have been felt locally for at least five days prior to the eruption (Martin, 1913; Fenner, 1925), but none of them were recorded instrumentally. Lower flows of the stack continue for an additional 1.5 km southwest along the caldera rim; a 100-m-thick rim flow extends 500 m beyond the base of the buttress, then thins to 25 m before pinching out atop products of SW Katmai (Fig. Abbreviations: KPKatmai Pass; NNovarupta rhyolite dome; KRdfKatmai River pumiceous debris-flow deposit of June 1912. This unit and the rhyolite (unit krh) are discussed further in the section titled Youngest Eruptive Units. A few remnants of Pliocene and early Quaternary volcanic rocks (Hildreth et al., 2004) cap peaks and ridges near Mount Griggs, but most such rocks have been eroded from the area surrounding the Valley of Ten Thousand Smokes. Unit khi, Horseshoe Island dacite dome; unit kwa, remnant of pre-1912 agglutinated dacite fallout that mantles west rim and peak 6128 and thickens into a pre-1912 crater (Figs. On right skyline 20 km away, ice-clad Mount Mageik rises beyond twin peaks of Mount Katmais west rim (seen in Fig. Low point visible on rim is at 5000 ft (1525 m) elevation; camera at 250 ft (75 m) asl. Rhyodacite crag (unit krs) in South Notch, at center, is same as viewed from north in Fig. A wedge of coarse yellow-brown breccia as thick as 12 m is widespread on the calderas northwest rim (Fig. It also brought worldwide attention to a little known and obscure region of the Alaska Territory. Although the crystal-poor flows are seen to rest exclusively on Jurassic basement, they contain common angular xenoliths of plagioclase-rich pyroxene andesite, which were evidently entrained, either at the vent or high on the edifice. Agglutinate sheet continues beneath talus up slope at left and over and beyond summit of peak. Eruptive sequence of June 1912, showing estimated timing and magma volumes of eruptive units, magnitudes (Ms) of earthquakes accompanying caldera collapse, stratigraphic positions of main mud layers ejected from collapsing caldera, intervals of ashfall at Kodiak village (160 km downwind), and fluctuating proportions of rhyolite, dacite, and andesite pumice that erupted concurrently. Nonetheless, study of circum-caldera hydrothermal explosion deposits intercalated with Novarupta pumice-fall layers (Hildreth, 1991) and analysis of the seismic record for June 1912 (Abe, 1992) together permitted a fairly good reconstruction of the fitful collapse sequence (Hildreth and Fierstein, 2000), as summarized in Figure 23. The inclined seismic zone is well defined and 2030 km thick (Kienle et al., 1983). Two substantial glaciers west and south of the caldera exhibit inconsistent behavior. Bears are plentiful, however, some of the most populous areas of the park include Chiniak Bay, Geographic Harbor, Hallo Bay, Kaflia Bay, Kukak Bay, and Kuliak Bay. The acid-altered white package (Fig. Shelf of densely agglutinated stratified dacite fallout (unit kwa), thinning from 20 m to 10 m against foot of peak 6128, viewed southwestward from West Notch on caldera rim. NE Katmai began with a steep mafic cone, dated at 89 25 ka, that has >800 m of relief on the caldera wall and includes virtually the only Quaternary basalt in the Katmai region. Magma reservoir of 1912 is depicted (just before eruption) as a unitary chamber zoned from andesite (A) to dacite (D) to rhyolite (R) in the proportions (1:4.5:8) erupted. 8). 29). One of the best places to see them is from the observation deck at Brooks Falls. Abrupt truncation of the NNW Buttress, thinning of its shelf-forming andesite stack farther southwest, and the generally lower rim along the northwest wall of the caldera probably all reflect erosion by an edifice-mantling Pleistocene ice cap that flowed preferentially toward the valley that in 1912 became the Valley of Ten Thousand Smokes. Additional (unlocated) adjustments in the vent, caldera, caldera-fill, or magma-storage and plumbing systems continued for more than two months, as recorded by a magnitude 6.1 earthquake at 2104 on 11 June, a magnitude 6.2 earthquake at 0128 on 17 June, and an abundance of felt seismicity (not recorded instrumentally) that persisted at least through mid-August (Martin, 1913). It was shown that 87Sr/86Sr ratios for 55 samples from the arc-front centers in the Katmai cluster (Martin, Mageik, Trident, Katmai, and Snowy) exhibit a general trend toward more radiogenic values in more evolved rocks (fig. Flows were emplaced down 20 slope, probably over snow, enhancing autobrecciation and allowing some to drape over eroded or collapsed ledges of their predecessors. At the East Notch, a stack of dacite lava flows (5) from SW Katmai that forms the middle section of the southeast wall abuts and unconformably overlaps the sequence (4b) from NE Katmai (Fig. Things To Do: Bear watching, sport fishing, boating, and backcountry hiking and camping are just a few of the many activities you can enjoy. Displaced volume is modeled alternatively as conical funnel and cylindroid, each having top surface area (4 km2) equal to that of caldera floor. Alaska Peninsula crust is thought to be 3036 km thick farther to the northeast (Moore et al., 1991), as well as near the peninsulas southwest extremity (Fliedner and Klemperer, 2000). 26; Layers A through B2), which in turn rested on glacial ice, which has since melted. Parents refers to a larger category under which an object falls. The source area was a snow-mantled glacier 4 km2 in area that sloped 1114 southward and was blanketed by at least 5 m of pumiceous fallout. In other places, the pyroclastic flows change color from light at the base to dark near the top. Chemical analysis shows it strongly depleted in Na, Ca, and Mg, relatively enriched in Al, Fe, S, and H2O, and probably originally andesitic. These latest Pleistocene or early Holocene units were correlated by microprobe analysis of glass and Fe-Ti oxides (Fierstein, 2007). Along the east wall south of the summit, strata of the mafic cone dip 2530S and continue below the East Notch where they disappear beneath lake level (Fig. Individual flows are 2550 m thick and are eroded into a stair-step stack of ledges separated by rubbly autobreccias. Media and Press for The Bears of Brooks Falls, The Novarupta-Katmai Eruption of 1912Largest Eruption Eruption of the 20th Century Centennial Perspectives, Early September Bearcam Questions and Answers, Inspiration at Katmai Pass | Wandering at Large, Become a friend of the Katmai Conservancy, Fitz's favorite books about bears and salmon. The North Ridge extends 1.7 km northward as a sharp cleaver (Fig. Thirty-three of the 50 shocks had surface-wave magnitudes (Ms) greater than 5.5, and 14 were in the range Ms 6.0 to 7.0. A daily commercial shuttle bus traverses a 37-km-long dirt road from Brooks Camp to the Overlook Cabin, a visitor center perched on a scenic knoll near the terminus of the ash-flow sheet in the Valley of Ten Thousand Smokes. Andesitic lava flows and breccias are major components of both subedifices of Mount Katmai, and products more mafic than 55% SiO2 are limited. (1) The truncated face of the North Ridge, which towers as high as 6450 ft (erroneously shown as 6100 ft on topographic maps), consists of a stack of pyroxene-dacite lava flows (66% SiO2) and thick autobreccias (Fig. "Thank goodness. Decker, R., and Decker, B., 1989, Volcanoes: W.H. 3, 6, and 7). 7 and 8). 30) indicate small crustal contributions to most Trident, Katmai, and 1912 magmas, the combined Nd, Sr, and O isotope results show that the rhyolite magma was not substantially a partial melt of the Mesozoic and older stratified rocks constituting the Alaska Peninsula basement. Glaciers white; Knife Creek Glaciers numbered 15. 3) is avalanche debris consisting of late Tertiary or early Quaternary andesite from Noisy Mountain, on the south slope of which the headwall scarp extends as high as 900 m above the valley floor. Mount Katmai has long been recognized for its caldera collapse during the great pyroclastic eruption of 1912 (which vented 10 km away at Novarupta in the Valley of Ten Thousand Smokes), but little has previously been reported about the geology of the remote ice-clad stratovolcano itself. Three lava domes were emplaced at unknown times after Episode III: PDPhantom dome, dacite plug explosively destroyed and distributed around Novarupta vent to produce block bed that overlies Layer H; HIHorseshoe Island dacite dome on caldera floor; NNovarupta dome, 95% rhyolite but streaked with andesite and dacite. Summit 6715 and the 1-km-long, knife-edged rim south of it (Fig. 25). Together, the lava and pumice are unique among products of the Katmai volcanic cluster in having 71%72.3% SiO2 and nearly unique in containing hornblende microphenocrysts. Within the wall embayment below the West Notch (Fig. 13). The Quaternary volcanic front trends narrowly N65E along the Katmai segment of the Aleutian arc (Fig. The deposit is an unstratified sheet of poorly sorted 1912 ash and pumice lapilli. Lowest flow near center of image and rim flow at upper left are both 80 m thick. The Noisy Mountain landslide deposit in upper Katmai Canyon (Fig. The precipitous inner walls of the 1912 caldera remain too unstable for systematic sampling; so we provide instead a photographic and interpretive record of the wall sequences exposed. Because the arc-front 87Sr/86Sr values correlate with fractionation indices, we infer that intracrustal contributions govern the Sr budget to a greater degree than does the subduction component (Hildreth et al., 2004). Note that 1912 andesite ejecta alone span 87Sr/86Sr range for entire 1912 suite. Freeman, New York, 285 p. Fierstein, J., and Hildreth, W., 1992, The plinian eruptions of 1912 at Novarupta, Katmai National Park, Alaska: Bulletin of Volcanology, v. 54, p. 646-684. He suggested but could not confirm that Jurassic sedimentary rocks cropped out near the base of the caldera wall. In 1912, magma flowed beneath Mount Katmai and exploded through the Novarupta volcano. The sheet also dips northeastward off the peak as steeply as 35 before leveling off near the West Notch (Fig. Figure 30 presents 87Sr/86Sr data for Mount Katmai, Trident, and the 1912 eruption, plotted against such a fractionation index (1/Sr). Sedimentary rocks have been reported at an elevation of over 6,000 feet (1,830m) in the west wall of the caldera and near the bottom of the eastern wall near 3,400ft (1,040m). The Katmai area is renowned for grizzly bears and just seeing one is a highlight for most people. 3). (10,915 sq. Mount Katmai has long been recognized for its caldera collapse during the great pyroclastic eruption of 1912 (which vented 10 km away at Novarupta in the Valley of Ten Thousand Smokes), but little has previously been reported about the geology of the remote ice-clad stratovolcano itself. At center of notch, 50-m-high knob is dacite lava flow and breccia (64.4% SiO2) that extends north (to left) over strata of the NE Katmai edifice. Although these were deprived of contributions from higher on the foundered edifice, each remains actively crevassed and shrinkage is limited to the notches on the caldera rim. Abbreviations for other geographic features: BBrooks Camp; BLBrooks Lake; BRBrooks River; DPDumpling Mountain; IBIliamna Bay; HBHallo Bay; KBKatmai Bay; KFKaflia Bay; KGKaguyak Bay; KKKukak Bay; KMKamishak Bay; KNKinak Bay; KVKatmai village; PBPortage Bay; and PUPuale Bay (called Cold Bay in 1912). Reaching Novarupta requires a day-long backpack trip, each way. Exposure in image, 35 m high, displays upward transition from explosively emplaced surge (altered), fall, and agglutinate deposits to effusive andesitic lava flows. This might simply reflect glacial and fluvial erosion, but the many 50- to 150-m-thick glassy columnar andesite flows around the southern foot of Mount Katmai suggest that thick glacial ice could have generally prevented them from crossing the valley. For a while we could neither think nor act in a normal fashion., Griggs had discovered a transformed Ukak River valley.

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