| Age or interval1 (in years) | Age control2 | Composition | Unit or event |
| <6845 | paleomagnetic pole position; superposition |
andesite, rhyodacite |
Postcaldera volcanism: Merriam Cone, Wizard Island, and rhyodacite platform |
| 6845 +/- 45 | radiocarbon age; paleomagnetic pole position | mafic andesite, andesite, rhyodacite | Climactic eruptions: (1)Plinian eruption of air-fall tephra; (2) Wineglass Welded Tuff; (3) collapse of caldera concurrent with emplacement of ash-flow deposits and backflow of Cleetwood lava into caldera; (4) phreatic (?) ejection of intracaldera debris |
| 7015 +/- 45 | radiocarbon age; paleomagnetic pole position | rhyodacite | Eruption of lower pumice fall from Llao Rock eruptive center |
| 6845 - 7200 (?) | radiocarbon age; paleomagnetic pole position; superposition | rhyodacite | Emplacement of four lava flows and associated tephra: Redcloud (oldest), Llao Rock and Grouse Hill (relative age between those two not well established), Cleetwood (youngest). |
| >12,000 (?) | glaciated; paleomagnetic pole position; superposition | basalt, mafic andesite | Vents outside Mazama shadow zone. Ages vary and are poorly constrained; one may be Holocene. |
| 22,000-26,000 | radiocarbon age; lies on glaciated surface; glaciated | dacite | Palisade flow erupted from vent south of Palisade Point. |
| 22,000-30,000 | lies on glaciated surface; glaciated; paleomagnetic pole position; superposition | basalt, mafic andesite, andesite, dacite | Forgotten Crater complex; eruption of basalt and mixed intermediate lavas from west-northwest-trending radial fractures. |
| 22,000-30,000 | glaciated; superposition | dacite(?) | Emplacement of dome east of Llao Rock. |
| 22,000-30,000 (?) | glaciated | dacite(?) | Sharp Peak domes; erupted on northeast-trending radial fractures. |
| 22,000-50,000 | lies on glaciated surface; glaciated; paleomagnetic pole position; superposition | dacite | Debris-flow and lithic-pyroclastic flow deposits in Munson Valley, Sun Valley, and on west caldera rim; probably represent dome emplacement high on southwest flank. |
| 30,000-50,000 | lies on glaciated surface; glaciated; preliminary K-Ar whole-rock age; superposition | andesite, dacite | Middle Wisconsin lava flows; present on southwest, north, and northeast wall. |
| 50,000-60,000 | lies on glaciated surface; superposition | dacite | Tephra and local lava flows of "Pumice Castle" and ash-flow deposits on southwest wall. |
| 50,000-60,000 | glaciated; lies on glaciated surface; superposition | dacite | Lavas of Scott Bluffs; may belong to early part of "Pumice Castle" eruptive episode. |
| 50,000-75,000 | lies on glaciated surface; glaciated; superposition | andesite, dacite | Early Wisconsin lava flows; some probably emplaced near boundary between oxygen isotope stages 3 and 4. |
| >50,000 | superposition | mafic andesite | Lava sheets of Cloudcap Bay |
| 60,000-75,000 | lies on glaciated surface; superposition | -- | Early Wisconsin glacial deposits. |
| 67,000-73,000 (?) | glaciated; preliminary K-Ar whole-rock age; superposition | andesite | Lavas and tephra of Hillman Peak. |
| 75,000-110,000 | glaciated; superposition | -- | Hydrothermal alteration of most pre-Wisconsin units exposed on caldera walls; may have been multiple episodes, some of which could be older than 110,000 years B.P. |
| 110,000-115,000 | lies on glaciated surface; preliminary K-Ar whole-rock age; superposition | andesite, dacite | Lava flows and domes and lithic-pyroclastic-flow deposits of Merriam Point. |
| 110,000-185,000 | glaciated; preliminary K-Ar whole-rock age | mafic andesite, andesite | Lava sheets of Llao Bay. |
| 75,000-340,000 | lies on glaciated surface; glaciated; superposition | andesite, dacite(?) | Lava flows of Sentinel Rock; extensive glacial erosion of under-lying lavas suggest flows are younger than approximately 250,000 years (Shackleton and Opdyke, 1973). |
| 190,000-340,000 | glaciated; preliminary K-Ar whole-rock age; superposition | andesite, dacite | Lavas of Dutton Cliff. |
| 340,000 | glaciated; preliminary K-Ar whole-rock age; superposition | andesite, dacite | Lavas of Danger Bay. |
| 400,000 | preliminary K-Ar whole-rock age; superposition | andesite(?) | Phantom Cone lavas and pyroclastic rocks. |
| >340,000 | glaciated; superposition | rhyodacite | Southern rhyodacitic lava flows; may or may not be related to Mazama magmatic system. |
| >75,000 | glaciated | All(?) -- basalt, mafic andesite, andesite, dacite, rhyodacite | Mount Scott and other volcanic rocks east of caldera; may or may not be related to Mazama magmatic system; mafic cones may be younger than 75,000 years. |
|
1Interval refers to bracketing dated units or events and does not
indicate the duration of an event. Ages based on preliminary K-Ar dates are
rounded.
2Radiocarbon ages are of associated soil or carbonized wood; preliminary K-Ar whole-rock ages are from M.A. Lanphere (written commun., 1981, 1982); paleomagnetic pole position dates from D.E. Champion (written commun., 1981, 1982). |
|||
| Table format modified by: Lyn Topinka, USGS/CVO, 1998, 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, p.57-115 | |||
Return to:
[Report Menu] ...
[Crater Lake Caldera Menu] ...
[Crater Lake Eruptive History Menu] ...
