Scientists have detected a supposedly rejuvenating uplift near the Three Sisters Volcano in Oregon. Using satellite imagery and sophisticated GPS instruments, geophysicists at the Cascade Volcano Observatory detected a subtle increase in surface uplift rates about 3 miles (5 kilometers) west of Oregon's three sister volcanoes.
Geologists have previously observed an increase in the rate of ascent in this area, and now the volcano's alert level and color code are still normal/green.
Data from satellite radar images show that between the summer of 2020 and August 2021, about 0.9 inches or 2.2 centimeters (about the width of an adult's thumb) occurred in an area 12 miles (20 kilometers) in diameter. Since August 2021, GPS data from a volcano monitoring station near the uplift center has measured at least 0.2 inches (0.5 centimeters) of the uplift.
The satellite radar interferogram spanned June 19, 2020 to August 13, 2021, and showed ground motion in the direction of the satellite. Red indicates a maximum bulge of about 2.2 centimeters (0.85 inches), which is located in the western part of the Southern Sisters. HuSB's consecutive GPS sites are marked by large black dots. Earthquakes that occur within the time period spanned by the interferogram are represented by small black dots.
In addition, seismologists observed brief small seismic eruptions in October 2021, December 2021, and January 2022. Most of these shallow earthquakes are too small to be accurately located, and those that are located are within the uplifted area.
Dan Dzurisin, a geologist at the U.S. Geological Survey, has set up a portable GPS monitoring device near Sister Mountain in central Oregon to track geological movements that have been going on for 25 years and are still in progress today. This is the uplift of the region west of the South Sister Volcano, the subtle rise of the surface.
The rise began in the mid-1990s and was first observed in radar satellite imagery. The U.S. Geological Survey, in partnership with the Forest Service, installed permanent monitoring stations to track the rate of uplift in the area. In addition, every summer, Dr. Dzurisin sets up a GPS station to collect ground deformation data. While radar satellites provide images of the entire area, these temporary GPS stations can measure the movement of individual points very accurately.
One thing that can cause uplifts is that magma moves underground, or magma in particular rises from greater depths on Earth to shallower depths, which forces the surface to move upward over a very wide area. It is worth noting that this process causes very few earthquakes. So if you don't use satellite radar data or other forms of data to look for it, an event like this might have happened elsewhere, maybe in central Oregon, just because we don't know.
Scientists at the U.S. Geological Survey are monitoring this activity as carefully and thoroughly as possible and will continue to monitor the area as long as it continues to gain more insight into the process.
The rise in the ground occurred in the same region in the mid-1990s. In the 25 years from 1995 to 2020, the center of the area rose by about 12 inches or 30 centimeters (equivalent to the height of a 2-liter soda bottle). While the current uplift rate is slower than the maximum rate measured in 1999-2000, it is significantly faster than the rate observed in the years before 2020.
The reason for the rise is a small pulse of magma accumulating about 4 miles (7 kilometers) below the surface. While any magmatic intrusion can eventually lead to a volcanic eruption, there may be detectable, more intense earthquakes, ground movements (deformations), and geochemical changes before the eruption. In general, when magma moves upward during an intrusion, it causes sustained or accelerated uplifts that fracture rocks to produce swarms of earthquakes and release large amounts of volcanic gases such as carbon dioxide. At the moment, we have not detected any of these signs.
CVO scientists will closely monitor the data in the coming months and release further data if necessary.