DESCRIPTION:
Mount Mazama Volcano and Crater Lake Caldera, Oregon

CraterLake05_aerial_crater_lake_mount_scott_12-10-05.jpg
Aerial view, Crater Lake, Wizard Island, and Mount Scott, as seen from the west.
USGS Photograph taken on December 10, 2005, by Mike Doukas.
[medium size] ... [large size]

Crater Lake Caldera

Location: Oregon

Latitude: 42.93 N

Longitude: 122.12 W

Height: 2,487 meters (8,156 feet - Hillman Peak)

Type: Caldera

Number of eruptions in the past 200 years: 0

Latest Eruptions: 4,000 years ago ² ... at least 800-900 years ago (Wizard Island) ³.

Present thermal activity: None

Remarks: Largest known eruption from Cascade Range volcano. Catastrophic, caldera-forming eruption 7,000 years ago; post-caldera lava and domes ² ... From a probable altitude of roughly 12,000 feet, the top of former Mount Mazama was lost to eruption and collapse that left the present huge crater and the deepest lake (1,932 feet) in North America. Explosive eruptions built Wizard Island and two other cones (submerged) on present crater floor ³.

Crater Lake caldera formed by collapse during the catastrophic eruption of approximately 50 cubic kilometers of magma, 6,845 carbon-14 years B.P. (before present). The 8x10 kilometer caldera lies in the remains of Mount Mazama, a Pleistocene stratovolcano cluster covering 400 square kilometers in the southern Oregon Cascades. Prior to its climactic eruption, Mount Mazama's summit had an elevation between 3,300 meters and 3,700 meters (10,800 - 12,000 feet). Its southern and southeastern flanks were deeply incised by glacial valleys, now beheaded, that form U-shaped notches in the caldera wall.

Mazama was one of the major volcanoes of the High Cascades and is the largest edifice between Mount Shasta and the Three Sisters volcanoes. Around Mazama are monogenetic cinder cones, lava fields, and small shield volcanoes that produced calc-alkaline basalt and andesite, primitive tholeiite, and rare shoshonitic andesite. These range in age from around 600,000 years to perhaps 40,000 years ago, and are similar to monogenetic volcanoes up and down the High Cascades.

Individual stratovolcanoes and shields that make up Mount Mazama become younger in a west-northwest sense. The oldest Mazama lavas dated are flows near lake level at Phantom Ship and the lavas of Mount Scott (around 400,000 years). The youngest stratovolcano is Hillman Peak (around 70,000 years). Local andesite flows on the north rim are 50-40,000 years old.

Post-caldera volcanic landforms are present beneath the lake surface and poke through to form Wizard Island. The central platform, Merriam Cone, and Wizard Island are all andesite evidently erupted within a few hundred years of caldera collapse. The small rhyodacite dome 30 meters belows lake level one kilometer east of Wizard Island is the youngest feature. ...

Crater Lake is located in Southern Oregon on the crest of the Cascade Mountain range, 100 miles (160 kilometers) east of the Pacific Ocean. It lies inside a caldera, or volcanic basin, created when the 12,000 foot (3,660 meter) high Mount Mazama collapsed 7,700 years ago following a large eruption.

Generous amounts of winter snow, averaging 533 inches (1,354 centimeters) per year, supply the lake with water. There are no inlets or outlets to the lake. Crater Lake, at 1,958 feet (597 meters) deep, is the seventh deepest lake in the world and the deepest in the United States. Evaporation and seepage prevent the lake from becoming any deeper.

The lake averages more than five miles (8 kilometers) in diameter, and is surrounded by steep rock walls that rise up to 2,000 feet (600 meters) above the lake's surface.

Following the collapse of Mount Mazama, lava poured into the caldera even as the lake began to rise. Today, a small volcanic island, Wizard Island, appears on the west side of the lake. This cinder cone rises 760 feet (233 meters) above the lake and is surrounded by black volcanic lava blocks. A small crater, 300 feet (90 meters) across and 90 feet (27 meters) deep, rests on the summit. The crater is filled by snow during the winter months, but remains dry during the summer.

The lake level fluctuates slightly from year to year. The highest level was reached in 1975 when the water level rose to 6,179.34 feet (1,883.47 meters) above sea level. The lowest level was recorded in 1942 when it dropped to 6,163.20 feet (1,878.55 meters). For such a deep lake, the maximum observed variation of 16 feet (5 meters) is minor (less than 1 percent).

Mount Mazama and Crater Lake caldera lie at the intersection of the Cascade chain of volcanoes with the Klamath graben, a north-northwest trending basin bounded by faults whose displacement is mainly vertical. At this latitude, the western margin of the Basin and Range province, characterized by north-south to northwest-southeast trending faults, impinges upon the Cascades. Focusing of volcanism at Crater Lake and the development of the shallow magma chamber which fed the climactic eruption are linked to this regional tectonic situation.

North and south of Crater Lake are many shield volcanoes of modest size and many more cinder cones with associated lava flow fields. Both represent short-lived activity at isolated vents. These monogenetic volcanoes are manifestations of regional volcanism throughout the Oregon Cascades.

Mount Mazama is the name applied to the volcano in which Crater Lake caldera formed. Before the caldera-forming eruption, the summit of Mount Mazama stood at ~3,700 meters (~12,000 feet) elevation. Mount Mazama was constructed during the last approximately 400,000 years by episodic growth of many overlapping shield and composite volcanoes, each of which probably was active for a comparatively brief period (Bacon, 1983). The erupted magma was mainly andesite. As the volcanic complex evolved, so did its eruptive style, such that the last ~70,000 years saw more highly explosive eruptions of silicic magma (dacite and rhyodacite). In the last ~30,000 years, the only record of activity, prior to the caldera-forming climactic eruption of ~7,700 years ago, was limited to a small number of preclimactic pyroclastic eruptions and ensuing lava flows of rhyodacite. Subsequent to the climactic eruption, all volcanic activity has occurred within the caldera itself. Wizard Island is a cinder cone and lava flows of postcaldera andesite, erupted soon after the caldera formed. Several more postcaldera volcanoes are hidden by the lake.

[Map,38K,InlineGIF]
Generalized Geologic Map of Mount Mazama and Vicinity
-- Modified from: Bacon, et.al., 1997, USGS Open-File Report 97-487

Local Native Americans witnessed the collapse of Mount Mazama and kept the event alive in their legends. One ancient legend of the Klamath people closely parallels the geologic story which emerges from today's scientific research. The legend tells of two Chiefs, Llao of the Below World and Skell of the Above World, pitted in a battle which ended up in the destruction of Llao's home, Mt. Mazama. The battle was witnessed in the eruption of Mt. Mazama and the creation of Crater Lake.

1853

In the spring of 1853, eleven miners from Yreka, California stopped in for supplies at Isaac Skeeter's mercantile store in Jacksonville, Oregon (approximately 90 miles south of Crater Lake). They began bragging that they knew how to find the legendary "Lost Cabin" gold mine. Skeeters quickly gathered up ten other Oregonians and set out, using the information overheard in his store. The trip was financed by John Wesley Hillman, a 21 year old who had recently returned home from a successful trip to the California goldfields. On June 12, three members from this party came upon a large body of water sitting in a huge depression. Hillman exclaimed that it was the bluest water he had ever seen. Skeeters suggested the name "Deep Blue Lake." Lack of provisions soon drove the miners down the mountains and back to Jacksonville where they reported the discovery of the lake. However, without the prospects of gold and fear of the unknown region to the north, there was no interest in confirming this discovery. It was soon forgotten.

1862

In 1862, another party of Oregon prospectors explored this area of the Cascade Range, including Crater Lake. The leader, Chauncy Nye, subsequently wrote a short article for the Jacksonville Oregon Sentinel. His article stated, "The waters were of a deeply blue color causing us to name it Blue Lake". This piece is the first published description of the lake.

1865

Hostilities between settlers and Native Americans developed in the area. In response, the U.S. Army established Fort Klamath seven miles southeast of the present park boundary in 1863. This led to the construction of a wagon road from Prospect in the Rogue River Valley to the newly established Fort Klamath. On August 1, 1865, the lake was "rediscovered" by two hunters attached to the road crews. Several soldiers and civilians journeyed to see the now-legendary lake. One of the participants, Sergeant Orsen Stearns, was so awestruck by what he saw that he climbed down into the caldera and became the first non- Native American to reach the shore of Crater Lake. Captain F. B. Sprague soon joined him and suggested the name "Lake Majesty."

1869

In July, 1869, newspaper editor Jim Sutton and several others decided to visit Lake Majesty and explore it by boat. By August, a canvas boat had been constructed and lowered onto the lake. Five people reached Wizard Island and spent several hours exploring the cinder cone. Sutton wrote an article describing the trip for his Jacksonville newspaper. Instead of Lake Majesty, Sutton substituted the name "Crater Lake" for the crater on top of Wizard Island.

1869-1918

William Gladstone Steel devoted his life and fortune to the establishment and management of Crater Lake National Park. His preoccupation with the lake began in 1870. In his efforts to bring recognition to the park, he participated in lake surveys that provided scientific support. He named many of the lake's landmarks, including Wizard Island, Llao Rock, and Skell Head. Steel's dream was realized on May 22, 1902 when President Theodore Roosevelt signed the bill giving Crater Lake national park status. And because of Steel's involvement, Crater Lake Lodge was opened in 1915 and the Rim Drive was completed in 1918.

In 1886, Steel assisted with the mapping of the lake, which had been undertaken by Clarence Dutton for the U.S. Geological Survey. During the original survey, soundings of the lake were conducted using pipe and piano wire. The maximum depth determined by the survey was 1,996 feet {608 meters), only 64 feet off from the sonar measurement of 1,932 feet officially recorded in 1959.

Mount Mazama was formed over a period of nearly half a million years by a succession of overlapping volcanoes. The first eruptions about 420,000 years ago built Mount Scott, located just east of Crater Lake. Over the next several hundred thousand years, Mount Scott and other nearby volcanoes became extinct, while new volcanoes grew to the west. Layers of lava flows from these volcanoes are visible in the caldera walls and in landmarks along the south rim of Crater Lake, including Applegate and Garfield Peaks. During the growth of Mount Mazama, glaciers repeatedly carved out classic U-shaped valleys. Some were filled with lava from later eruptions, while others, such as Kerr Notch and Sun Notch, were not. By about 30,000 years ago, Mount Mazama began to generate increasingly explosive eruptions that were followed by thick flows of silica-rich lava, an outward sign of the slow accumulation of a large volume of highly explosive magma deep beneath the volcano. Grouse Hill and Redcloud Cliff are thick lava flows erupted between 30,000 and 25,000 years ago. Another such eruption about 7,900 years ago formed a white layer of pumice and ash and the thick lava flow of Llao Rock. Within 200 years of the eruption at Llao Rock, another thick lava flow erupted near present-day Cleetwood Cove. These eruptions reached a peak 7,700 years ago in the largest explosive eruption in the Cascades during the past 1 million years.

Mount Mazama is the name applied to the volcano in which Crater Lake caldera formed. Before the caldera-forming eruption, the summit of Mount Mazama stood at ~3,700 meters (~12,000 feet) elevation. Mount Mazama was constructed during the last approximately 400,000 years by episodic growth of many overlapping shield and composite volcanoes, each of which probably was active for a comparatively brief period (Bacon, 1983). The erupted magma was mainly andesite. As the volcanic complex evolved, so did its eruptive style, such that the last ~70,000 years saw more highly explosive eruptions of silicic magma (dacite and rhyodacite). In the last ~30,000 years, the only record of activity, prior to the caldera-forming climactic eruption of ~7,700 years ago, was limited to a small number of preclimactic pyroclastic eruptions and ensuing lava flows of rhyodacite. Subsequent to the climactic eruption, all volcanic activity has occurred within the caldera itself. Wizard Island is a cinder cone and lava flows of postcaldera andesite, erupted soon after the caldera formed. Several more postcaldera volcanoes are hidden by the lake.

From the unabridged Webster's dictionary: From mazame (see mazama) from Nahuatl "mazatl" (deer) "A name applied by early writers to various American ruminants supposed to be the Rocky Mountain Goat." The club founders thought that the strongest climber in the mountains (the goat) was an appropriate symbol. The southern Oregon mountain that collapsed and became Crater Lake (Mt. Mazama) was named for the club.

Crater Lake caldera formed by collapse during the catastrophic eruption of approximately 50 cubic kilometers of magma, 6,845 carbon-14 years B.P. (before present). The 8x10 kilometer caldera lies in the remains of Mount Mazama, a Pleistocene stratovolcano cluster covering 400 square kilometers in the southern Oregon Cascades. Prior to its climactic eruption, Mount Mazama's summit had an elevation between 3,300 meters and 3,700 meters (10,800 - 12,000 feet). Its southern and southeastern flanks were deeply incised by glacial valleys, now beheaded, that form U-shaped notches in the caldera wall.

Mazama was one of the major volcanoes of the High Cascades and is the largest edifice between Mount Shasta and the Three Sisters volcanoes. Around Mazama are monogenetic cinder cones, lava fields, and small shield volcanoes that produced calc-alkaline basalt and andesite, primitive tholeiite, and rare shoshonitic andesite. These range in age from around 600,000 years to perhaps 40,000 years ago, and are similar to monogenetic volcanoes up and down the High Cascades.

Beneath the eastern half of Mount Mazama and extending to the southeast is an extensive field of rhyodacite flows and doms, apparently 700-600,000 years old, covering at least 350 square kilometers. Hornblende dacite underlies the rhyodacite in the southeastern part of the field. Generally north-south trending normal faults cut monogenetic vent lavas and rhyodacite, with most displacement down to the east. The same faults cut older Mazama flows, but dispalcements are not evident in the younger lavas and no tectonic faults have been detected in the caldera walls.

Individual stratovolcanoes and shields that make up Mount Mazama become younger in a west-northwest sense. The oldest Mazama lavas dated are flows near lake level at Phantom Ship and the lavas of Mount Scott (around 400,000 years). The youngest stratovolcano is Hillman Peak (around 70,000 years). Local andesite flows on the north rim are 50-40,000 years old. Shields are composed of sheet flows of agglutinated mafic andesite that are typically around 5 meters thick and form bands on the caldera walls. More viscous magma of andesite and dacite flows resulted in thicker flow units, up to 30 meters with larger proportions of flow-top rubble to dense lava. Even so, most of these also appear to be composed of agglutinated bombs. Undercooled inclusions of crystal-poor andesite magma are common in many andesite and dacite flows. Such flows make up Mount Scott (2,271 meters), east of the caldera rim, and Phantom Cone and other centers evident in the southern caldera walls. Some andesite lava flowed into glacial valleys forming thick intracanyon flows, such as at Sentinel Rock. At many places in the caldera walls and on the flanks of Mazama exposures of small glassy columns and piles of monolithologic glassy breccia provide evidence of lava/ice interaction. Many flows bury glaciated lava surfaces.

Explosive silicic eruptions occurred at several vents around 70,000 years ago. The most impressive was at Pumice Castle on the east wall, where layers of a dacitic Plinian fall deposit become densely welded near their vent. The deposit is non-welded to the south and in poor exposures on the north caldera wall from Cleetwood Cove to Steel Bay. Other welded dacite pumice fall deposits occur on the north side of Cloudcap and in the wall beneath the east flank of Llao Rock. Dacite pyroclastic flow deposits are present below Llao Rock and in the southwest wall. The Watchman flow is also dacite, as are monolithologic breccias and lithic-pyroclastic-flow deposits in the had of Munson Valley. Dacite forms the silicic endmember in the basalt-andesite-dacite mingled lavas of William Crater (formerly Forgotten Crater). There is no evidence of andesitic or dacitic volcanism between 40,000 years ago and the climactic eruption.

Rhyodacitic magma erupted as pumice and lava flows between 30 and 25,000 years ago at Grouse Hill, Steel Bay, and Redcloud Cliff. All are hornblende phyric, chemically evolved rhyodacite that apparently leaked from the growing climactic magma chamber, Sharp Peak and adjacent rhyodacite domes form a northeast-trending linear array that probably vented in the latest Pleistocene or early Holocene. They are compositionally identical with climactic rhyodacite (70% SiO2). The Llao Rock flow and preceding Plinian fall deposit were erupted 7,015 years ago and are zoned from 72 to 70 percent SiO2. The Cleetwood flow and pumice were erupted 100-200 years later, because the flow was still hot when the caldera collapsed during the climactic eruption at 6,845 years B.P. Cleetwood and climactic rhyodacites are compositionally homogeneous and identical. This rhyodacite makes up around 90 percent of the volume of climactic ejecta.

An interesting variation of a composite volcano can be seen at Crater Lake in Oregon. From what geologists can interpret of its past, a high volcano -- called Mount Mazama -- probably similar in appearance to present-day Mount Rainier was once located at this spot. Following a series of tremendous explosions about 6,600 years ago, the volcano lost its top. Enormous volumes of volcanic ash and dust were expelled and swept down the slopes as ash flows and avalanches. These large-volume explosions rapidly drained the lava beneath the mountain and weakened the upper part. The top then collapsed to form a large depression, which later filled with water and is now completely occupied by beautiful Crater Lake. A last gasp of eruptions produced a small cinder cone which rises above the water surface as Wizard Island in, and near the rim, of the lake.

Crater Lake caldera formed by collapse during the catastrophic eruption of approximately 50 cubic kilometers of magma, 6,845 carbon-14 years B.P. (before present). The 8x10 kilometer caldera lies in the remains of Mount Mazama, a Pleistocene stratovolcano cluster covering 400 square kilometers in the southern Oregon Cascades. Prior to its climactic eruption, Mount Mazama's summit had an elevation between 3,300 meters and 3,700 meters. ...

The climactic eruption began as a plinian column producing a widespread fall deposit mainly to the north-northeast. This column eventually collapsed and generated at least four flow units which colled together to form the Wineglass Welded Tuff. The Wineglass is present only on the north and east flanks of Mazama, and thus the vent for this valley-hugging ignimbrite was north of the summit. Eruption of the Wineglass ceased with onset of caldera collapse when highly mobile pyroclastic flows, derived from many vents, traveled radially down the flanks of the mountain to fill all the major drainages. Near the caldera and on all high ground these ring-vent-phase deposits consist of lithic breccia, while pumiceous ignimbrite occupies the valleys. This deposit is spectacularly compositionally zones: homogeneous rhyodacite (70% SiO2) followed by andesite (<61% SiO2) and mafic cumulate scoria (to as low as around 48% SiO2). ...

Timing of caldera collapse is well documented, because the interior of the Cleetwood flow was sufficiently plastic at the time of the climactic eruption that remobilizsed lava flowed northeast in response to seismicity and also down the caldera wall at Cleetwood Cove. Scarps on the brittle flow surface expose Plinian fall deposit and thin Wineglass Welded Tuff, but the proximal lithic breccia of the ring-vent-phase ignimbrite is banked agains them, indicating disruption of the Cleetwood flow surface after emplacement and welding of less than 2 meters of Wineglass but beofre deposition of the last lithic breccia. Thick, densely welded Wineglass in paleovalleys at the caldera rim sagged towards the caldera, showing that collapse took place before complete solidification fo this ignimbrite.

Crater Lake occupies a caldera formed 6,850 years ago during the climactic eruption of Mount Mazama which was a cluster of Pleistocene stratovolcanoes. A period of 15,000-40,000 years was required to form the silicic component of the climactic magma chamber. During that period, eruptions of basalt, andesite, dacite, and rhyolite occurred in the Mount Mazama area.

During the few centuries preceding the climactic eruption, at least two small- to moderate-volume (<1 to several cubic kilometers) eruptions of rhyolite occurred in the area underlain by the magma chamber. Tephra from one of these eruptions extended into southeastern Oregon and western Nevada and the same tephra, or one or more others, fell as far away as eastern Washington. The explosive eruptions were followed by the extrusion of rhyolite lava flows.

The climactic eruptions 6,850 years ago produced voluminous tephra-fall and pyroclastic-flow deposits. The tephra deposits are about 40 centimeters thick at points 200 kilometers northeast of the volcano and 4-5 centimeters thick at 1000 kilometers; layers have been found in 8 western states and 3 Canadian provinces. The tephra fall was followed by two episodes of pyroclastic-flow formation. The first was of small extent, but it was followed by voluminous pyroclastic flows that moved outward in all directions to distances of as much as 60 kilometers. The total volume of magma erupted during the climactic eruption was about 50-60 cubic kilometers, which is an order of magnitude larger than that produced during any other explosive eruption in the Cascade Range during postglacial time.

Following the climactic eruption, an andesite scoria cone and lava flows were erupted within the caldera to form Wizard Island. The initial postcaldera eruptions probably occurred shortly after the climactic eruption, prior to the development of the lake. Other eruptions occurred after the lake had begun to form. A rhyolite dome on the flank of the Wizard Island volcano records the youngest known eruptive activity.

New investigations of the geology of Crater Lake National Park necessitate a reinterpretation of the eruptive history of Mount Mazama and of the formation of Crater Lake caldera. Mount Mazama consisted of a glaciated complex of overlapping shields and stratovolcanoes, each of which was probably active for a comparatively short interval. All the Mazama magmas apparently evolved within thermally and compositionally zoned crustal magma reservoirs, which reached their maximum volume and degree of differentiation in the climactic magma chamber approximately 7,000 years B.P.

Summary of the eruptive history of Mount Mazama -- Modified from: Bacon, 1983

The history displayed in the caldera walls begins with construction of the andesitic Phantom Cone, approximately 400,000 years B.P. Subsequently, at least 6 major centers erupted combinations of mafic andesite, andesite, or dacite before initiation of the Wisconsin Glaciation approximately 75,000 years B.P. Eruption of andesitic and dacitic lavas from 5 or more discrete centers, as well as an episode of dacitic pyroclastic activity, occurred until approximately 50,000 years B.P.; by that time, intermediate lava had been erupted at several short-lived vents. Concurrently, and probably during much of the Pleistocene, basaltic to mafic andesitic monogenetic vents built cinder cones and erupted local lava flows low on the flanks of Mount Mazama. Basaltic magma from one of these vents, Forgotten Crater, intercepted the margin of the zoned intermediate to silicic magmatic system and caused eruption of commingled andesitic and dacitic lava along a radial trend sometime between approximately 22,000 and 30,000 years B.P. Dacitic deposits between 22,000 and 50,000 years old appear to record emplacement of domes high on the south slope. A line of silicic domes that may be between 22,000 and 30,000 years old, northeast of and radial to the caldera, and a single dome on the north wall were probably fed by the same developing magma chamber as the dacitic lavas of the Forgotten Crater complex. The dacitic Palisade flow on the northeast wall is approximately 25,000 years old. These relatively silicic lavas commonly contain traces of hornblende and record early stages in the development of the climatic magma chamber.

Some 15,000 to 40,000 years were apparently needed for development of the climactic magma chamber, which had begun to leak rhyodacitic magma by 7015 +/- 45 years B.P. Four rhyodacitic lava flows and associated tephras were emplaced from an arcuate array of vents north of the summit of Mount Mazama, during a period of approximately 200 years before the climactic eruption. The climactic eruption began 6845 +/- 50 years B.P., with voluminous airfall deposition from a high column, perhaps because ejection of approximately 4-12 cubic kilometers of magma to form the lava flows and tephras depressurized the top of the system to the point where vesiculation at depth could sustain a Plinian column. Ejecta of this phase issued from a single vent north of the main Mazama edifice but within the area in which the caldera later formed. The Wineglass Welded Tuff of Williams (1942) is the proximal featheredge of thicker ash-flow deposits downslope to the north, northeast, and east of Mount Mazama and was deposited during the single-vent phase, after collapse of the high column, by ash flows that followed topographic depressions. Approximately 30 cubic kilometers of rhyodacitic magma were expelled before collapse of the roof of the magma chamber and inception of caldera formation ended the single-vent phase. Ash flows of the ensuing ring-vent phase erupted from multiple vents as the caldera collapsed. These ash flows surmounted virtually all topographic barriers, caused significant erosion, and produced voluminous deposits zoned from rhyodacite to mafic andesite. The entire climactic eruption and caldera formation were over before the youngest rhyodacitic lava flow had cooled completely, because all the climactic deposits are cut by fumaroles that originated within the underlying lava, and part of the flow oozed down the caldera wall.

A total of approximately 51-59 cubic kilometers of magma was ejected in the precursory and climactic eruptions, and approximately 40-52 cubic kilometers of Mount Mazama was lost by caldera formation. The spectacular compositional zonation shown by the climactic ejecta -- rhyodacite followed by subordinate andesite and mafic andesite -- reflects partial emptying of a zoned system, halted when the crystal-rich magma became too viscous for explosive fragmentation. This zonation was probably brought about by convective separation of low-density, evolved magma from underlying mafic magma. Confinement of postclimactic eruptive activity to the caldera attests to continuing existence of the Mazama magmatic system. ...

The age of the lower pumice fall (Llao vent) is 7015 +/- 45 years, on the basis of radiocarbon dating of carbonized twig fragments from the upper (approximately) 1 centimeter of a 15-centimeter-thick soil developed on glacial drift beneath the deposit at the Wineglass. ... Ash beds that are apparently correlative with the lower pumice fall are present in northern Washington (Mack, et.al., 1979), approximately 700 kilometers (435 miles) from Crater Lake, in eastern Washington (Blinman, et.al., 1979), near Steens Mountain, southeastern Oregon (Blinman, et.al., 1979; P.J.Mehringer, oral commun., 1982), and in the Lake Lahontan area, western Nevada (Tsoyawata Bed of Davis, 1978; J.O. Davis, written commun., 1982). The lower pumice fall must have been deposited over a period of at least several days in order for sufficient variation in wind direction to occur to account for the wide dispersal. The volume of magma equivalent to the lower pumice fall deposits is probably around 2-10 cubic kilometers. ...

The climactic, caldera-forming eruption of Mount Mazama (6,845 +/- 50 years B.P.) can be divided into two phases: single vent and ring vent. Onset of collapse of the caldera probably caused the switch from the first to the second phase of eruption; the timing of this switch can be documented through stratigraphic relations. ... Deposits of the single-vent phase consist of two units erupted successively from the same vent area: the climactic pumice fall and the Wineglass Welded Tuff of Williams (1942). The climactic pumice fall represents air-fall deposition from a high Plinian column; the Wineglass Welded Tuff was deposited by ash flows derived from a collapsed column. ... Deposits of the climactic pumice fall account for a large part of the material erupted during the single-vent phase. ...

The widespread Mazama tephra has been used extensively as a stratigraphic marker. Much of the climactic pumice fall was carried to the northeast; only sparse, thin patches of redeposited pumice are present near the caldera rim around the southwest quadrant. The informally-named Mazama ash is >50 centimeters thick (20 inches) at Newberry Volcano, 110 kilometers (68 miles) from Crater Lake, and >1 centimeter thick (less than 1/2 inch) in southwestern Saskatchewan, 1,200 kilometers (745 miles) from its source. ...

MORE Mazama Ash Information

CraterLake82_crater_lake_and_wizard_island_09-82.jpg
Crater Lake and Wizard Island.
USGS Photograph taken in September 1982 by Lyn Topinka.
[medium size] ... [large size]

Following the collapse of Mount Mazama, lava poured into the caldera even as the lake began to rise. Today, a small volcanic island, Wizard Island, appears on the west side of the lake. This cinder cone rises 760 feet (233 meters) above the lake and is surrounded by black volcanic lava blocks. A small crater, 300 feet (90 meters) across and 90 feet (27 meters) deep, rests on the summit. The crater is filled by snow during the winter months, but remains dry during the summer.

From a probable altitude of roughly 12,000 feet, the top of former Mount Mazama was lost to eruption and collapse that left the present huge crater and the deepest lake (Crater Lake - 1,932 feet) in North America. Explosive eruptions built Wizard Island (at least 800-900 years ago) and two other cones (submerged) on present crater floor.

The only volcanic features in the Crater Lake area younger than the climactic eruption occur within the caldera. Williams (1961) interpreted the geology of the caldera floor on the basis fo bathymetric data obtained by the U.S. Coast and Geodetic Survey (1959) and samples dredged by Nelson (1961). No subaerial tephra deposits correlative with postcaldera events have been recognized. Recent investigations (Nelson, 1967; Nelson et.al., 1980; Williams and Von Herzen, 1983) lead to some important revisions.

Merriam Cone, a small (approximately 0.1 cubic kilometer) olivine-bearing andesitic vent on the north margin of the caldera floor, is the smallest of three distinguishable volcanic features. The caldera floor partly surrounding Merriam Cone owes its comparatively flat surface to sedimentary fill (Nelson, et.al., 1980), not to lava flows, as suggested by Williams (1961). Wizard Island forms the subaerial part of a voluminous pile of presumably similar andesitic material. The Wizard Island edifice accounts for approximately 1 to 2 cubic kilometers of magma, depending on where its base is drawn. Like Merriam Cone, the Wizard Island andesitic magmas were erupted near the inferred structural margin of the caldera.

The broad platform east of Wizard Island suggests silicic lava flows or coalescing domes. At the west end of this platform is a small dome composed of hornblende rhyodacite. The bathymetric map suggests that the platform may extend beneath the north side of the Wizard Island pile. Nelson (1961), however, did not report any Wizard Island tephra in dredge hauls from the platform or the rhyodacite dome, and so it may be that some silicic volcanism occurred after the last andesitic eruptions. The volume of silicic lava erupted was between approximately 0.5 and 2 cubic kilometers, depending on tis extent beneath and west of the dome. Erupted inboard of the two andesitic centers, the rhyodacite is about as differentiated as the most evolved magma of the climactic chamber (Bacon and Smith, unpubl.data, 1981). The postcaldera rhyodacite may represent either (1) uppermost climactic magma, which escaped eruption prior to formation of the caldera, or (2) the first leak from a new batch of silicic magma regenerated after the climactic eruption. ...

Whatever the ages, relative or absolute, of the postcaldera eruptive units the Mazama magmatic system apparently remains the focus of volcanic activity for a large region. Areas of very high heat flow on the caldera floor provide evidence for ongoing hydrothermal circulation (Williams and Von Herzen, 1983), and the elevated chloride and sodium contents of lake water relative to other surface waters may indicate a component of geothermal fluid (J.M.Thompson, unpubl. data, 1981; Williams and Von Herzen, 1983).

[Map,25K,InlineGIF]
Geologic Map of Crater Lake Caldera Floor
-- Modified from: Bacon, et.al., 1997, USGS Open-File Report 97-487

An interesting variation of a composite volcano can be seen at Crater Lake in Oregon. From what geologists can interpret of its past, a high volcano -- called Mount Mazama -- probably similar in appearance to present-day Mount Rainier was once located at this spot. Following a series of tremendous explosions about 6,600 years ago, the volcano lost its top. Enormous volumes of volcanic ash and dust were expelled and swept down the slopes as ash flows and avalanches. These large-volume explosions rapidly drained the lava beneath the mountain and weakened the upper part. The top then collapsed to form a large depression, which later filled with water and is now completely occupied by beautiful Crater Lake. A last gasp of eruptions produced a small cinder cone which rises above the water surface as Wizard Island in, and near the rim, of the lake.

Crater Lake caldera formed by collapse during the catastrophic eruption of approximately 50 cubic kilometers of magma, 6,845 carbon-14 years B.P. (before present). The 8x10 kilometer caldera lies in the remains of Mount Mazama, a Pleistocene stratovolcano cluster covering 400 square kilometers in the southern Oregon Cascades. ...

Post-caldera volcanic landforms are present beneath the lake surface and poke through to form Wizard Island. The central platform, Merriam Cone, and Wizard Island are all andesite evidently erupted within a few hundred years of caldera collapse. The small rhyodacite dome 30 meters belows lake level one kilometer east of Wizard Island is the youngest feature.

The only volcanic features in the Crater Lake area younger than the climactic eruption occur within the caldera. ... Merriam Cone, a small (approximately 0.1 cubic kilometer) olivine-bearing andesitic vent on the north margin of the caldera floor, is the smallest of three distinguishable volcanic features. ... Wizard Island forms the subaerial part of a voluminous pile of presumably similar andesitic material. The Wizard Island edifice accounts for approximately 1 to 2 cubic kilometers of magma, depending on where its base is drawn. ... The broad platform east of Wizard Island suggests silicic lava flows or coalescing domes. At the west end of this platform is a small dome composed of hornblende rhyodacite. ...

Lake researchers have discovered two areas on the lake bottom affected by hydrothermal spring water. Mineral-rich water, at a slightly elevated temperature, pools in some locations and leaves iron deposits in others. Communities of bacteria mark the venting sites.

Between 1980 and 1984, the U.S. Geological Survey's David A. Johnston Cascades Volcano Observatory (CVO) established baseline geodetic networks at Mount Baker, Mount Rainer, and Mount St. Helens in Washington, Mount Hood and Crater Lake in Oregon, and Mount Shasta and Lassen Peak in California. To this list of potentially active volcanoes, CVO extended its monitoring program in 1985 to include Newberry and South Sister volcanoes in central Oregon. The Newberry and South Sister networks were re-measured in 1986 and will be measured periodically in future years. Improvements since 1984 in the recording of endpoint and flightline temperatures resulted in better overall data than obtained previously. The improvements included: calibration of all the sensors and precision thermistors, installation of a new recording system for flightline data, and recording of endpoint temperatures 6 meters above ground level. The data collected in 1985 and 1986 indicate little or no apparent deformation at either volcano between surveys.

In addition to locating regional earthquakes, the Pacific Northwest Seismograph Network (PNSN), in cooperation with the Cascades Volcano Observatory, is also responsible for monitoring seismic activity at volcanoes in the Pacific Northwest. The PNSN currently operates seismometers on or near Mount Adams, Mount Rainier, Mount St. Helens, Mount Hood, Mount Baker, Three Sisters, and Crater Lake.

Crater Lake Monitoring Menu

Crater Lake National Park attracts approximately 500,000 visitors per year, with the high season being July and August. Crater Lake National Park is located in southern Oregon on the crest of the Cascade Range, 100 miles from the Pacific coast. The National Park was established in 1902 and encompases 183,244 square miles. The 33-mile Rim Drive around Crater Lake is a two lane road that has more than 20 scenic overlooks. From mid-October until mid-June, the north entrance and Rim Drive are closed to the public due to deep snow and ice buildups along the road. Rim Drive around the east side of the lake can be closed earlier than mid-October and may not open until July. Deer and other wildlife crossing the road and icy conditions at any time of the year provide hazards to drivers.

Crater Lake National Park is accessible from the south and north via Oregon Highways 62 and 138, respectively. A paved road runs around the caldera rim. Access to the lake is limited to the trail at Cleetwood Cove, where tour boats provide a good close-up view of the caldera walls.

"Visit A Volcano" - Crater Lake National Park

[Map,24K,InlineGIF]
Geologic Map, Crater Lake Caldera Floor and Caldera Walls, with Points of Interest
-- Modified from: Bacon, et.al., 1997, USGS Open-File Report 97-487

Chaski Bay Landslide

• Geologic evidence for the rapid formation of Crater Lake caldera by catastrophic collapse during the climactic eruption of Mount Mazama indicates that most of the caldera wall dates from that time. However, the bench on the south wall, informally known as Chaski slide, wall-parallel lake-facing scarps near Garfield Peak, and similar faults mapped in the Sun Notch to Eagle Point area suggest that large blocks of the south wall have the potential to fail. Nelson and other (1988, 1994) described a landslide deposit on the lake floor from Chaski Bay to the center of the lake that apparently formed soon after the caldera collapse and the central platform volcano erupted but before a deep lake was present. -- Excerpt from: Bacon, et.al., 1997, Volcano and Earthquake Hazards in the Crater Lake Region, Oregon: USGS Open-File Report 97-487

Cleetwood Flow

• Within 200 years of the eruption at Llao Rock, another thick lava flow erupted near present-day Cleetwood Cove. -- From: Klimasauskas, et.al., 2002

Crater Lake

• Generous amounts of winter snow, averaging 533 inches (1,354 centimeters) per year, supply the lake with water. There are no inlets or outlets to the lake. Crater Lake, at 1,958 feet (597 meters) deep, is the seventh deepest lake in the world and the deepest in the United States. Evaporation and seepage prevent the lake from becoming any deeper. The lake averages more than five miles (8 kilometers) in diameter, and is surrounded by steep rock walls that rise up to 2,000 feet (600 meters) above the lake's surface. -- Excerpt from: U.S. National Park Service, Crater Lake National Park Website, 2001

Discovery Point

• Discovery Point is the site of John Wesley Hillman's "discovery" of Crater Lake in 1853. -- Excerpt from: U.S. National Park Service, Crater Lake National Park Website, 2001

Grouse Hill

• Grouse Hill and Redcloud Cliff are thick lava flows erupted between 30,000 and 25,000 years ago. -- Klimasauskas, et.al., 2002

Hillman Peak

• Hillman Peak is the westernmost andesitic stratocone in the cluster of polygenetic volcanoes that make up Mount Mazama. -- Excerpt from: Bacon, Charles R., 1983, Eruptive History of Mount Mazama and Crater Lake Caldera, Cascade Range, U.S.A.: Journal of Volcanology and Geothermal Research, v.18 (1983), p.57-115

• Hillman Peak is 1,980 feet (604 meters) above the water, highest point on the caldera rim -- Excerpt from: U.S. National Park Service, Crater Lake National Park Website, 2001

• Individual stratovolcanoes and shields that make up Mount Mazama become younger in a west-northwest sense. The oldest Mazama lavas dated are flows near lake level at Phantom Ship and the lavas of Mount Scott (around 400,000 years). The youngest stratovolcano is Hillman Peak (around 70,000 years). Local andesite flows on the north rim are 50-40,000 years old. -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.193-195, Contribution by Charles R. Bacon

Llao Rock

• 7,900 years ago, a white layer of pumice and ash and the thick lava flow of Llao Rock. -- From: Klimasauskas, et.al., 2002

Palisade Point

• Palisade Point is 507 feet (155 meters) above the water, lowest point on the caldera rim -- Excerpt from: U.S. National Park Service, Crater Lake National Park Website, 2001

Phantom Ship

• Individual stratovolcanoes and shields that make up Mount Mazama become younger in a west-northwest sense. The oldest Mazama lavas dated are flows near lake level at Phantom Ship and the lavas of Mount Scott (around 400,000 years). The youngest stratovolcano is Hillman Peak (around 70,000 years). Local andesite flows on the north rim are 50-40,000 years old. -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.193-195, Contribution by Charles R. Bacon

• Phantom Ship is 167 feet (51 meters) above the water. -- Excerpt from: U.S. National Park Service, Crater Lake National Park Website, 2001

Redcloud Flow

• Grouse Hill and Redcloud Cliff are thick lava flows erupted between 30,000 and 25,000 years ago. -- Klimasauskas, et.al., 2002

Mount Scott

• Individual stratovolcanoes and shields that make up Mount Mazama become younger in a west-northwest sense. The oldest Mazama lavas dated are flows near lake level at Phantom Ship and the lavas of Mount Scott (around 400,000 years). The youngest stratovolcano is Hillman Peak (around 70,000 years). Local andesite flows on the north rim are 50-40,000 years old. -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.193-195, Contribution by Charles R. Bacon

• Mount Scott - highest peak in the park, historic fire tower, strenuous climb, 1,500 foot rise. -- Excerpt from: U.S. National Park Service, Crater Lake National Park Website, January 2001

Wizard Island and Merriam Cone

• From a probable altitude of roughly 12,000 feet, the top of former Mount Mazama was lost to eruption and collapse that left the present huge crater and the deepest lake ( Crater Lake - 1,932 feet) in North America. Explosive eruptions built Wizard Island (at least 800-900 years ago) and two other cones (submerged) on present crater floor. -- Excerpt from: Foxworthy and Hill, 1982

• The only volcanic features in the Crater Lake area younger than the climactic eruption occur within the caldera. ... Merriam Cone, a small (approximately 0.1 cubic kilometer) olivine-bearing andesitic vent on the north margin of the caldera floor, is the smallest of three distinguishable volcanic features. ... Wizard Island forms the subaerial part of a voluminous pile of presumably similar andesitic material. The Wizard Island edifice accounts for approximately 1 to 2 cubic kilometers of magma, depending on where its base is drawn. ... The broad platform east of Wizard Island suggests silicic lava flows or coalescing domes. At the west end of this platform is a small dome composed of hornblende rhyodacite. -- Excerpts from: Bacon, Charles R., 1983, Eruptive History of Mount Mazama and Crater Lake Caldera, Cascade Range, U.S.A.: Journal of Volcanology and Geothermal Research, v.18 (1983), p.57-115

• Following the collapse of Mount Mazama, lava poured into the caldera even as the lake began to rise. Today, a small volcanic island, Wizard Island, appears on the west side of the lake. This cinder cone rises 760 feet (233 meters) above the lake and is surrounded by black volcanic lava blocks. A small crater, 300 feet (90 meters) across and 90 feet (27 meters) deep, rests on the summit. The crater is filled by snow during the winter months, but remains dry during the summer. -- Excerpt from: U.S. National Park Service, Crater Lake National Park Website, 2001

• See "Post-Climactic Eruption" above for MORE Wizard Island and Merriam Cone information

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