Western Cascades
Encyclopedia
Portions of this article include public domain
text from the USFS Deschutes & Ochoco National Forests - Crooked River National Grassland.
The Western Cascades is a region of Oregon
, USA containing many shield
volcano
es, cinder cone
s and lava flows. The region was volcanically active from approximately 5-0.5 million years ago. The province is characterized as an older, deeply eroded volcanic range lying west of the more recent snow-covered High Cascade Range
. They range in elevation from 1700 feet on the western margin to 5800 feet on the eastern margin. The Western Cascades began to form 40 million years ago with eruptions from a chain of volcanoes near the Eocene
shoreline. Volcanic activity gradually shifted to the east in the Miocene
and Pliocene
.
The Western Cascades are made up almost entirely of slightly deformed and partly altered volcanic flows and pyroclastic rocks which range in age from late Eocene to late Miocene. These rocks have been heavily dissected by erosion and the only evidence remaining of the many volcanoes from which they were erupted are occasional remnants of volcanic necks or plugs which mark former vents. There are also minor Pliocene to Pleistocene
intracanyon lavas derived from the High Cascades or rare local vents. From youngest to oldest, the Western Cascade Range consists of four main units:
Public domain
Works are in the public domain if the intellectual property rights have expired, if the intellectual property rights are forfeited, or if they are not covered by intellectual property rights at all...
text from the USFS Deschutes & Ochoco National Forests - Crooked River National Grassland.
The Western Cascades is a region of Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
, USA containing many shield
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
es, cinder cone
Cinder cone
According to the , Cinder Cone is the proper name of 1 cinder cone in Canada and 7 cinder cones in the United States:In Canada: Cinder Cone In the United States:...
s and lava flows. The region was volcanically active from approximately 5-0.5 million years ago. The province is characterized as an older, deeply eroded volcanic range lying west of the more recent snow-covered High Cascade Range
Cascade Range
The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades...
. They range in elevation from 1700 feet on the western margin to 5800 feet on the eastern margin. The Western Cascades began to form 40 million years ago with eruptions from a chain of volcanoes near the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
shoreline. Volcanic activity gradually shifted to the east in the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
and Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
.
The Western Cascades are made up almost entirely of slightly deformed and partly altered volcanic flows and pyroclastic rocks which range in age from late Eocene to late Miocene. These rocks have been heavily dissected by erosion and the only evidence remaining of the many volcanoes from which they were erupted are occasional remnants of volcanic necks or plugs which mark former vents. There are also minor Pliocene to Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
intracanyon lavas derived from the High Cascades or rare local vents. From youngest to oldest, the Western Cascade Range consists of four main units:
- 0 to 4 million year old intracanyon basaltBasaltBasalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
and basaltic andesiteBasaltic andesiteBasaltic andesite is a black volcanic rock containing about 55% silica. Minerals in basaltic andesite include olivine, augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central America and the Andes of South America. Basaltic andesite is common in...
flows from the High Cascade Range. - 4 to 9 million year old basalt and basaltic andesite flows with lesser amounts of andesite and daciteDaciteDacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
. These rocks which cap the highest Western Cascade ridges were erupted prior to uplift and faulting along the east margin of the Western Cascade Range. This unit is compositionally identical to unit 1 and other rocks of the High Cascade Range, and therefore was probably erupted from vents in and adjacent to the High Cascades. - 9 to 18 million year old basalt, basaltic andesite, and andesite lavas with lesser amounts of dacite tuffs and lavas.
- 18 to 40 million year old silicic tuffs and lavas. Units 3 and 4 were erupted from many vents west of known High Cascade volcanic centers, although some of these older vents may be buried beneath the High Cascade Range.
Notable Vents
| Name | Elevation | Location | Last eruption | |
| meters | feet | Coordinates | ||
| Armet Creek | - | - | - | ~0.56 million years ago |
| Bachelor Mountain | - | - | - | - |
| Battle Ax Mountain Battle Ax Mountain Battle Ax Mountain, officially known simply as Battle Ax, is a shield volcano in the Cascade Range of Oregon. The shield is mostly made of andesite.The summit is in the Bull of the Woods Wilderness and can be reached by the Battle Ax Mountain trail.... |
- | - | 44.9°N 122.2°W | 1-2 million years ago |
| Crescent Mountain | - | - | - | - |
| Harter Mountain | - | - | - | - |
| High Prairie (Oregon) | - | - | - | ~1.98 million years ago |
| Iron Mountain | - | - | - | - |
| Snow Peak | - | - | - | ~3 million years ago |
| Three Pyramids | - | - | - | - |
See also
- List of volcanoes in the United States of America
- Types of volcanic eruptionsTypes of volcanic eruptionsDuring a volcanic eruption, lava, tephra , and various gases are expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed...