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Crater Lake National Park SOUTHWEST

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Are~: 183,224acres;.287squaremiles

Phone:541-594-3100

Establishedasa National Park:May22, 1902 Address:P.O.Box7, CraterLake,OR97604

E-mail:[email protected] Website:www.nps.gov/crla/index.htm

Crater Lake, 21 square miles in size and over 1900 feet deep, lies in the caldera of a collapsed volcano. Mazama, one of the composite cones in the High Cascades, exploded in climactic eruptions nearly 7000 years ago. In 11!ulticoloredwalls, encircling the lake and rising 500 to 2000 feet from the water, are the records of intense volcanic and glacial activity during Mazama's construction and destruction. ~

Pumice pinnacles, a pumice /Idesert," plug domes, satellite craters, cinder cones, U-shaped valleys, and more are in this remarkable national park. 'C'

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northoverCraterLakeand WizardIsland.LlaoRockjuts out fromthe calderarim. NationalParkServicephoto by C. L.Summer.

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. . . The color of the water is ultramarine, bordered by turquoise along the shores. Set in majestic cliffs, it is a most attractive natural jewel... -1.S.

Diller, U.S. Geological Survey, 1911.

If you have seen Crater Lake, you can imagine how astonishing and mysterious it must have seemed to early visitors to Oregon Territory. John Wesley Hillman, a young prospector, came upon the place quite by accident in 1853 as he was following his mule up a ridge in search of a lost mine. When the mule suddenly stopped on the brink of a cliff, Hillman looked down over the edge and saw below the indigo water of the lake in its great caldera, a good five miles from rim to rim. He called it "Deep Blue Lake." The spot where he stood, on the southwest side of the rim, is now Discovery Point. Later, settlers in the region decided "Crater Lake" was the ideal name. This name has been retained, despite assertions by teachers, geologists, and park rangers that it should be called "Caldera Lake"! The lake's intense blue color is due to the purity of the water and the great depth of the caldera. Crater Lake's officially measured depth is 1932 feet, which makes it the deepest lake in the United States. The water, which has accumulated from rain and snow, contains little dissolved or suspended material. Measurements of visibility in this transparent water have reached depths of over 325 feet. The lake was devoid of aquatic life until some 60 years ago when fish were introduced. Freshwater shrimp had to be brought in first so that when the lake was stocked with trout, the fish would have something to eat. Except for minor seasonal changes, the level of the water remains fairly constant from year to year; the intake from precipitation balances loss from seepage and evaporation. Springs on the outer slopes of the caldera are fed by local ground water, not by subterranean discharge from Crater Lake. Summer temperatures of the lake water average 55° F; winter temperatures approach freezing, but the lake seldom freezes over. The seasonal and annual variability of Crater Lake make it an extremely complex and dynamic system. Monitoring programs involving consistent data collection have not been in place long enough for scientists to understand fully how the lake's ecosystem works, although considerable progress has been made since the Limnological Study (funded by Congress) began in the .

early 1980s. Nevertheless, except for the consequences of fish introductions, long-term changes caused by human activities could not be separated from changes caused by natural phenomena. For example, during a period in the 1970s, when the lake's clarity appeared to decrease, higher than expected nitrate levels were found in water samples, especially from one of the springs in the caldera wall. As a precaution, a septic system's drain field was moved well away from the caldera rim. Since then nitrate level{have not changed significantly in the lake or the spring, but in 1994, researchers recorded the highest clarity readings to date in the lake. Since chemical analyses did not show a connection between the original drain field and the spring in question, it may be that the water in that spring has a natural source for the slightly higher nitrate readings. The main source of nitrogen in the lake water, about 90 percent, comes from the atmosphere. As a part of the study, a submersible was brought in to explore the lake floor. Helicopters landed the 7000pound submersible and more than 20,000 pounds of equipment on Wizard Island. Scientists who cruised the lake bottom in the submersible observed hydrothermal vents where they discovered blue saline pools, bacteria mats, and fields of moss (Weingrod 1995). An Oregonian, Judge William Gladstone Steel, was instrumental in the movement to preserve the Crater Lake region as a national park. As a boy in Kansas, he had read about a mysterious, deep blue lake in Oregon. When he was 18 years old, his family moved to Oregon, and soon young Steel began searching for the lake, asking all the oldtimers where it was. Finally, in 1885, after 13 years of searching, he stood on the caldera's rim and looked down at Crater Lake. Then and there, he decided that it must be protected and preserved. Geologist Clarence Dutton helped Judge Steel organize a U.S. Geological Survey party in order to gather scientific data to support their hopes for a national park. In 1886, members of the party carried in a 26-foot boat that they lowered into the lake. By making soundings with a pipe and piano wire in different parts of the lake, the men obtained a depth reading quite close to the official depth of today (1932 feet). Meanwhile, a topographer surveyed the caldera rim and vicinity and prepared the first map of Crater Lake. Steel gave names to many of the features.

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Highways into the park lead to a scenic drive around the caldera rim. Probably the best vantage point to see many features of geologic interest is the top of Mount Scott, reached by a trail from Rim Drive. Looking down one can see both volcanic and glacial landforms around the caldera, as well as an incomparable view of the lake. To the north and south rise the High Cascades, topped by snowcapped volcanoes. To the west is "a sea of peaks and ridges"-the Western Cascades. Beyond them, the more distant KlamathSiskiyou Mountains are seen. To the east stretches an immense platform of basalt (the Columbia River basalts) that goes farther than one can see into Idaho. The lava plateau is cut by canyons, and a few steepscarped, tilted, fault-block mountain ranges break the flatness of the surface in the distance.

GeologicFeatures Mazama'sVolcanicRocks Basalt, andesite, trachyte, and rhyolite are compositional varieties of dense-textured, extrusive igneous rocks, ranging from the darker basalts (higher in iron and magnesium, lower in silica) to light-colored rhyolite (lower in iron and magnesium, higher in silica). Dacite, a compositional variety containing principally plagioclase and quartz, is difficult to distinguish from rhyolite without the use of petrographic techniques. Much of the rock at Crater Lake is described as rhyodacite.

Pumice is a textural term for a frothlike volcanic glass that cooled from liquid lava during eruption.A typical pumice contains so much trapped air that it can float. The composition is usually that of rhyolite or trachyte. Tuff is a general term for consolidated rocks made up of pyroclastic fragments of various sizes. A tuff breccia, for example, consists of about half ash and half larger fragments. In a welded tuff, glass shards, hot ash, pumice, and cinders have been fused by hot gases and the weight and heat of overlying materials. Uneven compaction causes laminations and banding. The composition is highly siliceous. Scoria refers to cinders or a cindery crust that has a vesicular texture (full of holes). Escaping volcanic gases during the eruption and solidification of lava produce vesicular texture. Scoria, which is usually darker and heavier than pumice, is andesitic or basaltic in composition.

VolcanicFeatures The large caldera occupied by Crater Lake plus the encircling flanks and ridges are about all that is left of once-mighty Mazama. Its early history was similar to that of the other Cascade volcanoes. Like its contemporaries-Mount Rainier (Chapter 35) and Lassen (Chapter 37)-Mazama grew during the Pleistocene, while alpine glaciers advanced and retreated on its slopes. From its foundation rocks at the base (between 5000 and 6000 feet in elevation), Mazama rose another 6000 feet to an elevation of approximately 11,000 feet above sea level. The cone was broader and less steep than Shasta's or Rainier's because the subsidiary vents and overlapping cones gave the volcano a bulky, irregular shape. The present caldera rim is 7000 to 8000 feet above sea level, and geologists have estimated that the original cone probably rose 2500 to 3500 feet above that. Associated with the construction and destruction of Mazama are a variety of extrusive and intrusive features. Thick pumice and ash deposits, relics of the violent explosive eruptions, lie on the flanks of the mountain, relatively fresh and only mildly weathered by the elements since they fell. Some of the deposits are welded tuffs produced by fiery clouds and ash flows. The Pumice Desert, which stretches away to the north from the rim, is a very thick blanket of ash that is mostly devoid of vegetation. The pyroclastic material is too loose to hold water and too siliceous to develop soil or support much plant growth. The Pinnacles, an area of tall spires about 5 miles southeast of the rim, are erosional remnants of tuff deposits, 200 to 300 feet thick, ejected in flaming ash flows during the climactic eruptions. Steam clouds rose for years after the hot pyroclastics blanketed the slopes and filled the canyons. Where steam was localized, as in fumaroles, particles became cemented together in the shape of pinnacles, or spires, and were more resistant to erosion. Thin, hollow tubes, where gas escaped, still go down through the centers of some of the pinnacles (fig. 36.3). Associated Composite Cones Mount Bailey and Mount Thielsen, both a short distance north of the park, probably became inactive early in the Pleistocene, perhaps around the time that Mazama started up. Mount Scott, highest point in the park (8926 feet), developed as a parasitic cone from

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Mazama's eastern base. Mount Scott's very steep cone is made up of layers of andesite lava, closely related chemically to some of the earlier flows of Mazama. Evidently, Mount Scott became extinct before the end of the Pleistocene. A large cirque on the northwest side indicates glacial erosion that was not "repaired" by postglacial volcanic activity. Not much is left of Union Peak in the southwest corner of the park except its volcanic plug, an erosional remnant of lava that solidified to resistant rock in the neck of the volcano.

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Basalt lavas and andesitic basalts built a number of satellite cones and craters around Mazama. Crater Peak formed as a shield volcano of andesite and basalt flows and later erupted pyroclastics of andesite and dacite. Another shield volcano, Timber Crater, in the northeast corner of the park, is also made up of basalt and basaltic andesite flows, but its shield is capped by two cinder cones. None of the cinder cones are more than a thousand feet high from base to summit. Examples are Desert Cone, Bald Crater, Red Cone, and Diller Cone. Volcanic bombs (fragments of lava, or ejecta, usually rounded, ropey, or spiral, that hardened while in the air) lie on the cinder cones in myriad sizes and shapes. Some of the cinder cones are aligned on what seems to have been a fissure system tapping a magma chamber. Wizard Island, the large cinder cone in Crater Lake, resembles a wizard's hat, for which it was named. It formed in the caldera from eruptions after Mazama's collapse. The cone rises nearly 800 feet above lake level. Its well developed crater is 400 feet across and about 90 feet deep (fig. 36.1).

Dikes and Other Features of the CalderaWalls Most of the large andesite dikes exposed in the park are old conduits and radial fissure fillings that probably served as feeders for Mazama's flank eruptions. Devil's Backbone, which runs up the -cliffsof Crater Lake from the water's edge to the west rim, is the most conspicuous dike (fig. 36.4). A similar dike forms a high vertical wall immediately beneath the Watchman and merges upward into the Watchman lava flow (western rim). Phantom Ship, a much older eroded dike or conduit remnant, sticks out of the water near the lake's south shore (fig. 36.5B). ~

FIGURE 36.3 The Pinnacles, somefivemiles southeastof the calderarim,werefusedby hot gases escapingthroughmanyfeet of ashafterthe climatic eruptionover6,000yearsago.Erosionhasremovedthe thickcoverof looseash,leavingthe resistantpillars standingin the deepcanyonof SandCreek.Onthewall in the backgroundthe lowerlightareaof the welded tuff hasa rhyodacitecomposition,whilethe upper darkerareahasan andesiticor basalticcomposition. NationalParkServicephoto.

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thought to have been formed by a lava flow that filled a glacial trough; but more recent evidence indicates that the flow was emplaced in an explosion crater (Bacon, 1983). Feeder dikes of Hillman Peak are exposed in the remaining half of the old conduit that was laid bare by explosions that removed the eastern half of its cone (fig. 36.6). Hillman Peak, highest spot on the rim, was one of the parasite cones of Mazama and now reveals a nearly perfect cross section of its interior due to the blasting out' of the caldera. The unusual colors displayed in the caldera wallshues of yellow, buff, brown, orange, and faint purpleare the result of hydrothermal weathering of the volcanic rocks by ascending ground water and chemically charged gases. Caves in the caldera walls, mostly along the water level, are the result of the erosion of lavas or mudflows between lava flows. Some caves, also eroded from lava, are outside the rim.

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Dacite Domes Dacite flows that began erupting toward the end of Mazama's development tended to become thicker and more viscous. Some earlier dacite flows are overlain by andesite or by glacial drift. The later, more viscous dacites formed domes. Some, such as Lookout, Pothole, and Dry Buttes, are isolated domes. Others, like the group south and east of Mount Scott, are in

clusters.

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GlacialFeatures

FIGURE 36.4 The Devil's Backbone, a large andesitedikeexposedbyerosionof the soft materialin the caldera's westwall. NationalParkServicephoto.

Dacite dikes, several of which are clustered near Llao Rock, are smaller and less prominent. Llao Rock (fig. 36.1) was formed by a massive rhyodacite flow that came from near the bottom of a satellite cone that exploded, not long before Mazama's climactic eruptions. Because of its shape, Llao Rock was earlier

Between eruptions, when the mountain was quiet, glaciers rebuilt themselves and carved out deep valleys on the flanks of the volcano. When eruptive activities resumed, the glacial troughs provided convenient channels for hot lavas, ash flows, lahars, and glowing avalanches. The culminating eruptions and explosions truncated, or "beheaded," glacial valleys that extended from the high slopes to elevations lower than the present caldera rim. Kerr Valley and Sun Notch on the southeast side are spectacular U-shaped troughs beheaded by the explosions and now exposed in the precipitous caldera wall. Also exposed in the cliffs rising from the lake are horizons of glacial debris interspersed with layers of lava and pumice. Grooves of glacial striations come to the very brink of the cliffs; where layers of andesite jut out slightly from the cliff

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FIGURE 36.5 A Sun NotchandKerrNotch,U-shapedglacialtroughsbeheadedbythe explosionof Mazama, are separatedby Dutton Cliffs. National ParkServicephoto. ~

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FIGURE 36.5 B The PhantomShip is a remnant of a volcano that existedbefore Mount Mazama.It was coveredby the younger volcano and was not exposeduntil the calderaformed. National ParkServicephoto.

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FiGuRE.;36.6 HillmanPeakis 8100feet highon the caldera'swestrim. Pumicedepositsaridblocksof lava blanketthe slopebetweenthe peakandRimDrive.NationalParkServicephoto. walls, more striations can be discerned on the angular tops. This indicates that after a lava flow hardened, glaciers had time to abrade the surface (fig. 36.7). A large glacier on Mazama flowed down Munson Valley on the southwestern flank by the present location of park headquarters. Munson Glacier went on into Annie Creek Valley and down beyond the park's southern boundary, perhaps as far as Fort Klamath. Meltwater streams from the extensive glaciers of the southern and eastern slopes can:ied large quantities of outwash into the Klamath Marsh. On the west side, several glaciers joined and went down the valley of the Rogue River; while on the north slopes, the Mazama glaciers joined those of Mounts Bailey and Thielsen. Moraines are of many ages and types. Some are almost completely buried by pumice and by the ash of the culminating explosions. The youngest moraines were deposited after the explosions had ceased, indicating an interval of colder climate sometime within the past 6000 years. No glaciers exist in Crater Lake

National Park at the present time, but heavy snows fall each winter, about 50 feet from September through May.

Geologic History 1. Development of the Western Cascades, middle and late Tertiary time. Along the western part of the Cascade Range lies a belt of older lavas and pyroclastics that make up the Western Cascades. These mountains were folded and deeply eroded long before the Cascade volcanoes began to erupt. Both the Western Cascades and the younger High Cascades are the result of the continuing subduction of oceanic crust beneath the westwardmoving North American plate (box 35.1). None of the Tertiary volcanics are exposed in Crater Lake National Park; however, some of these rocks may underlie the base of Mazama.

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FIGURE 36.7 The grooveson theserocksperchedon the calderarimareglacialstriationsthat wereincisedby glacierson Mount Mazamalong before the climatic eruptions. National ParkServicephoto. ~'

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2. Miocene 4plift ~nd Pliocene volcanism; building of the High Cascades. As the volcanic mountain system was uplifted, it became a parrier to the moisture-carrying winds from the Pacific that dropped rain and snow on the slopes. Glaciers had probably begun to form at the higher elevations by the end of Miocene time. The High Cascades evolved as a north-south belt east of the Western Cascades, with younger volcanics overlapping older Tertiary rocks. Pliocene lava flows, mostly basalts and and.esites,built up lava plateaus and the older volcanoes near Crater Lake, such as Mounts Bailey and Thielsen and Union Peak. 3. Construction of Mazama in middle and late Pleistocene time. / The Mazama cone began to grow on top of Pliocene and Pleistocene lavas approximately 75,000 years ago. Mazama's summit may have attained about the same elevation as Lassen, Hood, and Bakeraround 11,000 feet-but never grew as high as Rainier and Shasta. Like the other Cascade volcanoes, Mazama was built up by mostly andesite lava flows and pyroclastic eruptions. The volcano had a number of parasitic cones and numerous flank eruptions. Mount Scott is the largest surviving satellite cone. 4. Pleistocene glaciations before, during, and after volcanic eruptions. Throughout much of its history, Mazama was capped by snow and ice. In the caldera wall, layers of glacial deposits are interbedded with lavas down to and below the lake surface. From this record, we can see that glaciers advanced and retreated many times, because of climatic variations and because of destruction by volcanic activity. When Mazama was at its maximum height, high peaks and ridges stuck up through the glacial ice. The absence of till at the top of Hillman Peak and Watchman suggests that these p~aks were never entirely covered by ice. Hillman Peak probably acted as a "cleaver," or arete, similar to Mount Rainier's cleavers that divide glaciers coming down from the summit (Chapter 35). Long periods of quiescence followed times of active eruptions. Bands of soil containing charred vegetation at the top of till deposits, later covered by lava flows and pumice, record such quiet times when reforestation of the slopes could take place.

It seems likely that the time of maximum glaciation was near the end of the andesitic eruptions and after the early dacitic flows that erupted mainly from fissures along the north side of the mountain. This activity may be the reason why glacial erosion was more severe on the south side. The large U-shaped valleys on the south side, Munson, Kerr, and Sun, were deeply excavated during this time. Glacial ice was probably a thousand feet thick in the troughs.

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5. Quiet ending of Pleistocene time; differentiation of magma. After Mazama had reached its maximum height, large-scale volcanic activity on the main cone ceased for about 40,000 years. In the interim, the Wisconsinan stage of glaciation came to a close. The discovery of carbonized stumps of trees that had been growing in till in a glacial col near Discovery Point implies that a long period of quiescence preceded the last catastrophic explosions. The pumice that buried the trees can be correlated with those explosions. The presence of trees on lower slopes also suggests that at the time of the explosions, the glaciers had receded to higher elevations on the mountain. Several miles below the surface of the High Cascades, magma collected and became concentrated in the magma reservoir while the volcanoes were relatively quiet. Mazama's magmatic system was reorganized and strengthened. Gradually a kind of chemical zoning took place in the magma chamber, with layers of lighter, more siliceous magma rising nearer the top and the denser, more mafic magma sinking toward the bottom. 6. The beginning of the end of Mazama. During the last few hundred years before the climactic eruptions, several vents along the northern slopes of Mazama began to "leak out" volcanic material. These dacitic eruptions of lava and pumice included the Llao Rock, Redcloud, and Cleetwood flows plus 'several others. During the brief, but very intense, Cleetwood flow, which directly preceded the culminating explosions, quantities of hot tephra were ejected, and blocks of old andesite from inside the summit were thrown out with the pumice.

7. Mazama'sclimactic eruptions 6845 :!:50 years ago. The single-vent phase. The initial tremendous explosion was sudden, thunderous, and violent. A huge

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column of fiery, gaseous pumice shot 5 to 10 miles high in the air at nearly twice the velocity of sound (fig. 36.8A). The column may have been a mile in diameter and perhaps "spouted" for more than a day. As it began to collapse, glowing avalanches sped down from the vent. Some became the intensely welded tuff of the Wineglass (northeast part of the caldera rim) (fig. 36.8B). The tephra ejected in the initial explosion was almost entirely rhyodacitic in composition. On the slopes and around the base of Mazama, many feet of ash and pumice fragments of various sizes

accumulated. Finer ash particles were carried many miles by the prevailing winds, principally toward the east and north. Deposits of various thicknesses fell over a considerable range, landing as far away as Alberta and Saskatchewan to the north, Nevada and northern California to the south; Idaho and Montana to the east, and even to the northwest corner of Yellowstone National Park in Wyoming (fig. 36.9). Radiocarbon dating of the Mazama ash layer places these eruptions at about 6845 years ago, with a plus-orminus factor of 50 years. However, some pollen studies

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FIGURE 36.9 The darkerareashownon the map was blanketed by varyingthicknessesof Mazamaash from the climactic eruption. Dust and ash, borne on prevailingwinds, alsofell farther to the east and northeast,far beyondthe PacificNorthwest. Modified after Williams 1942.

have yielded dates that nearly pinpoint the eruption. Dates from a bog in western Montana, in which pollen is associated with Mazama ash, place the ash fall within a maximum time "window" of only three years around the postulated 6845 years ago. Wherever a Mazama ash deposit is found, it provides a significant date of reference for geologists and archaeologists. Indian artifacts (mats, points, scrapers, etc.), preserved by Mazama ash, have been found at sites many miles to the east of Crater Lake. Geologists have been able to determine average rates of sedimentation in a number of lakes in the Pacific Northwest since the time of the Mazama ash falls. They can also tell which glacial moraines in the Cascades are younger than Mazama ash and which ones are older. The ring-vent phase: multiple vents. Due to the release of pressure and the rapid extrusion of large volumes of tephra, the cone's upper section could no

longer support its own weight. The whole summit area fractured and collapsed back into the volcano's center. A series of large glowing avalanches boiled out from vents all around the collapsing crater and roared down the mountain flanks, branching into the glacial valleys and spreading destruction everywhere. The whole mountain was set ablaze as trees and anything else combustible were incinerated. One fiery ash flow traveled 40 miles down the Rogue River valley. Another went north in the valley between Mounts Bailey and Theilsen, crossing Diamond Lake and then dumping pumice bombs into the valley of the North Umpqua River. Flows that went east carried large boulders of pumice many miles across the flats east of the volcano. To the south, some flows ended in the Klamath Marsh. Floating chunks of pumice, resembling styrofoam, were later washed down into the Klamath Lakes (fig. 36.8C). During the ring-vent phase, as collapse continued and the caldera began to form, some of the hot ash and lava flowed back into the volcano's center. The Cleetwood flow, which preceded the culminating explosion, had not completely cooled when it was flattened and rifted by backflow oozing down the caldera wall. The last eruptions apparently came from very deep in the magma chamber. Dark-colored scoria covered some of the light-colored pumice of the earlier avalanches. On the north side, dark scoria created Pumice Desert. Light and dark pumice layers are especially noticeable in the Pinnacles. After the eruptions had ended, the air was full of choking, acrid volcanic smog and dust. Heavy rains fell and clouds of steam and fine dust continued to billow upward. Pumice-filled canyons remained hot and smoking for years. When the dust finally settled and the air cleared, only a great pit was left where the cone had been. The caldera was 5 miles wide and 4000 feet deep (fig. 36.8D). How much of Mazama's previous bulk disappeared due to explosion and collapse? According to estimates based on a number of measurements, approximately 15 cubic miles of brecciated rock and pyroclastic material were engulfed by the collapse of the cone into the caldera. The volume of ejected and erupted material was even greater. In all, about 25 cubic miles of tephra were thrown out by the ash falls and ash flows.

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FIGURE 36.10 Schematicgeologic crosssectionacrossthe calderafloor of the present-dayCrater Lake(not drawn to scale).From C.H. Nelsonet al. 1994. GeologicalSocietyof America Bulletin, p. 701. @ GeologicalSocietyof America. Usedby permission. ~

8. Postcollapseactivity.

Volcanic features younger than the climactic eruptions developed only within the caldera and were by no means extensive. Lava oozed out over the caldera floor, constructing Wizard Island, Merriam Cone, smaller cones, the central platform, and, eventually, a rhyodacite dome. A variety of sediments accumulated on the caldera floor, for the most part during the first 2000 years after the great explosion. As the caldera cooled down, rain and snow collected, forming a lake. Large-scale wall failures around the rim formed avalanche debris fans; sheetwash moved loose materials into sediment aprons on the lakebed. Turbidites spread finer sediments over the basin plain. Steam vents, along with hydrothermal springs, were active during this time. As the caldera continued to be quiescent for many years, very fine sediments, consisting of airborne silt, ash, mudflows, and siliceous ooze, covered the older features in the lakebed (fig. 36.10). Around the caldera, the walls were attacked by the forces of erosion-landsliding, mud flows, freezing, and thawing. A brief recurrence of small glaciers at "

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higher elevations left drift patches on top of pumice. Running water reestablished a,radial drainage pattern as it tried to clear out the debris-choked valleys. After a time, dense forests grew around the base and up the slopes, hiding some of the scars.

Williams, H. 1942. The Geology of Crater Lake National Park, Oregon (with geologic map). Washington, D.C.: Carnegie Institution of Washington Publication 540.

Alt, D.D. and Hyndman, D.W. 1978. Roadside Geology of Oregon, Missoula, Montana: Mountain Press Publishing Co. Bacon, C.R. 1983. Eruptive History of Mount Mazama and Crater Lake Caldera, Cascade Range, U.S.A. Journal of Volcanology and Geothermal Research 18:57-115. -. 1987. Mount Mazama and Crater Lake Caldera, Oregon. Centennial Field Guide, Cordilleran Section,

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Hill, M. ed. v. 1. Boulder, Colorado: Geological Society of America. p. 301-306. -.1988. Crater Lake National Park, Oregon; Map and text on back of Map U.S. Geological Survey. Cranson, K.R. 1982. Crater Lake, Gem of the Cascades, the Geological Story of Crater Lake National Park, 2nd edition. Lansing, Michigan: KRC Press. Harris, S. L. 1988. Fire Mountains of the West: the Cascade and Mono Lake Volcanoes. Missoula, Montana: Mountain Press Publishing Co. Nelson, C.H.; Bacon, c.R.; Robinson, S.w.; Adam, D.P.; Bradbury, J.P.; Barber, J.H., Jr.; Schwartz, D.; and Vagenas, G. 1994. The Volcanic, Sedimentologic, and PaleolimnologicHistory of the Crater Lake Caldera Floor, Oregon: Evidence for Small Caldera Evolution. Geological Society of America Bulletin 106:684-704, May.

Orr, E.L.; Orr, W.N.; and Baldwin, E.M. 1992. Geology of Oregon, 4th ed. Dubuque, Iowa: KendallIHunt Publishing Company. p. 141-166. Weingrod, C. 1995. A Commitment to Clarity. National Parks 69:42-47, July/August. Williams, H. 1942. The Geology of Crater Lake National Park, Oregon (with geologic map). Washington, D.C.: Carnegie Institution of Washington Publication 540. -.1976. The Ancient Volcanoesof Oregon, 7th edition. Condon Lectures. Eugene, Oregon: Oregon State System of Higher Education.

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Note: To convert English measurements to metric, go to www.heipwithdiy.comlmetric_collversion_calctilator.htmi

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