USDA Forest Service
 

Deschutes & Ochoco National Forests
Crooked River National Grassland

Website Update - starting on Monday, May 16, you will be automatically redirected to our new website! We are excited to present a new face for the Deschutes and Ochoco National Forests and hope you enjoy it!

 
 

Deschutes National Forest
1001 SW Emkay Drive
Bend, OR   97702

(541) 383-5300

Ochoco National Forest
3160 N.E. 3rd Street
Prineville, OR   97754

(541) 416-6500

Crooked River National Grassland
813 S.W. Hwy. 97
Madras, OR   97741

(541) 475-9272

United States Department of Agriculture Forest Service.

Geology

Oregon Volcanoes

Middle Sister Volcano

SUMMARY

Type: stratovolcano
Activity: extinct
Last Eruption: estimated at about 50,000 yrs ago
Rock Type: predominantly basalt with andesite, dacite, and rhyodacite.
Eruptive Volume: ?
Latitude: 44.15 N
Longitude: 121.78 W
Location Maps: from TIGER Mapping Service

Topo Map from TopoZone

Middle Sister Photo Menu

GEOLOGIC BACKGROUND:

The Three Sisters area contains 4 large cones of Quaternary age -- North Sister, Middle Sister, South Sister, and Broken Top. 

  • North Sister and Broken Top are deeply dissected and probably have been inactive for at least 100,000 years. 
  • Middle Sister younger than the North Sister and older than the South Sister. It was active in late Pleistocene but not postglacial time. 
  • South Sister is the least dissected; its basaltic andesite summit cone has a well preserved crater. Most of South Sister predates late Wisconsin glaciation and is therefore older than 25,000 years; however, eruptions of rhyolite from flank vents have occurred as recently as 2000 years ago. 

HISTORIC ACTIVITY:

  • None

RECENT ACTIVITY:

  • During the period from about 10 am on March 23, 2004 to about 1 am on March 25 a swarm of earthquake occurred in the Three Sisters area. More than 100 small quake up to a magnitude of 1.9 occurred. Seismograms of swarm.

  • On May 8, 2001, U.S. Geological Survey scientists reported that by using Satellite Radar Interferometry (or InSAR) they had detected a broad area over which the ground has swelled upward slightly during the past few years.  The area is centered 5 kilometers (3 miles) west of South Sister volcano in the Three Sisters region of the central Oregon Cascade Range. The area of uplift is about 15 to 20 kilometers (9 to 12 miles) in diameter and the maximum amount of uplift at its center is about 10 centimeters (4 inches). 

 

DATA SOURCE:

  • USGS

ADDITIONAL INFORMATION

Geology Header Graphic
Page Counter

USDA Forest Service - Deschutes & Ochoco National Forests
Last Modified: Thursday, 25 March 2004 at 17:14:57 EDT


USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.