THREE SISTERS (OREGON)

The 'Three Sisters' are three volcanic peaks of the Cascade Volcanic Arc and the Cascade Range in Oregon, each of which exceed in elevation. They are the third, fourth, and fifth highest peaks in the state of Oregon and are located in the Three Sisters Wilderness, about southwest from the nearest town of Sisters, Oregon. The three peaks have 15 named glaciers among them, nearly half of all the 35 named glaciers in Oregon. The Sisters were named Faith, Hope, and Charity by early settlers.^[1]
'North Sister' is high and is oldest of the three,^[2]
with towering rock pinnacles and glaciers. It has not erupted since the late Pleistocene. It is the most dangerous climb of the Three Sisters, due to its level of erosion, and thus rockfall.
'Middle Sister' at is the smallest and most poorly studied. It is also the middle in age. No reports on its potential for eruptions have been made.
'South Sister' at is the youngest and tallest volcano of the trio. It is a stratovolcano which last erupted about 1600 years ago. It has an uneroded summit crater about in diameter, which holds a small crater lake known as Teardrop Pool which is usually frozen except during the summer. This is the highest lake in Oregon. The standard climbing route up the South Ridge of South Sister is a long, steep, non-technical hike that can be easily completed in a day by reasonably fit hikers. Popular starting points are the Green Lakes or Devil's Lake trailheads.

Contents

Recent history

References

External links

Recent history

South Sister is the focus of recent volcanic activities watch

In 2000, a satellite discovered that there was a deforming uplift 3 miles (5 km) south of the South Sister. This could mean that the mountain is awakening. It is also possible that magma involved with the deformation could stop moving towards the surface and cool underground and it is possible that it may be some time before any eruptive activity were to occur. The type of magma involved in the uplift, the amount present and its properties would determine the nature of any eruptive activity. Activity could range from quiet emission of lava flows to more explosive and destructive eruptions. In mid-2005, it seems unlikely that any severe or catastrophic eruption would occur if an eruption were to occur in the near future. An eruption might or might not be centered at the current summit crater. A new vent or vents could open at or near the location of the uplift, and might produce lava flows, new cinder cones or other small volcanoes, or both. Activity could occur in more than one location around the volcano.
At about 10 AM PST on Tuesday, 23 March2004, an earthquake swarm began with epicenters in the area of uplift. The hundreds of small earthquakes subsided over several days. USGS scientists had been expecting such earthquake swarms to accompany the uplift, and they are not considered precursory events to an eruption.
In September of 2005, scientists discovered a rising bulge about three miles southwest of the South Sister. The ground in a 100 square-mile (259 square km) area is rising at a rate of per year. Scientists believe that a lake of fluid (likely magma), 1 mile (1.6 km) across and 65 feet (20 m) deep has formed at a depth of below the unpopulated area. The pooling fluid could be shifting magma or the creation of a new volcano.

References

1. USGS Cascade Volcano Observatory: Three Sisters Volcanoes, Oregon
2. Geologic Map of the Bend 30-×60-Minute Quadrangle, Central Oregon

External links

★

★ ''Bulge on South Sister Slows Down'' -- Oregonlive.com

★ Forest Service information