Questions About Monitoring Yellowstone
What are the main monitoring instruments of the Yellowstone Volcano Observatory?
Activity leading to a possibly impending volcanic eruption or a large earthquake can be evaluated using the modern seismic and GPS networks of YVO. The instruments are designed to provide information in near real time using modern digital instrumentation and internet and telephone links.
What techniques does YVO use to measure ground deformation?
Our primary techniques for measuring ground deformation are GPS and InSAR, defined below. Scientists study ground deformation or movement of the earth's surface at volcanic sites to help them to determine what could be happening at depth. An injection of magma at depth can move the ground up (inflation) whereas magma draining out of a system, from an eruption or movement elsewhere, can cause the ground to subside (subsidence). Ground movement can be a precursor to magma moving towards the surface but there is evidence of ground movement at many volcanic systems for hundreds to thousands of years without an eruption.
There are a variety of techniques that can be used to monitor ground deformation. Early measurements were made by measuring distances with rulers or special measuring sticks to determine vertical ground movements. Electronic distance measurements (EDM - an instrument that both sends and receives an electromagnetic signal) were later used to determine horizontal movements and tiltmeters (like a sophisticated carpenter's level) were used to measure vertical motions. Originally, this type of monitoring could only occur when someone was able to go into the field to perform a measurement at each station.
Recent technological advances have allowed for continuous monitoring by some instruments using satellite relays to send the data to scientists. Two of the more recent instruments are the Global Positioning System (GPS) and InSAR (Interferometric Synthetic Aperture Radar). Both are very useful for collecting specific information about a system and when used together become a more powerful tool. GPS can be used to measure horizontal and vertical motions at a specific site. To study large areas, multiple GPS receivers are used to form a network. GPS has the advantage that data are collected continuously, allowing for use as a routine monitoring tool.
In contrast, InSAR measures a large area from space at one point in time. It can be used to observe a region as it changes over a period of months or years. InSAR cannot be used as a routine monitoring tool because the data are currently collected infrequently and take time to purchase and process. InSAR's great advatage is that it provides a detailed map view of the specific areas that have undergone changes. We currently use a combination of GPS and InSAR at Yellowstone to determine ground deformation.
Have uplift and subsidence been seen on other volcanoes? Does uplift mean that an eruption is coming?
Uplift and subsidence have been observed at scores of volcanoes. Most volcanoes around the world show some evidence of uplift prior to eruption. The May 18, 1980 eruption of Mt. St. Helens was preceded by the outward growth of the volcano's entire north flank by more than 80 meters (that's 80,000 mm or 262 feet) and 2 months of intense activity that included more than 10,000 earthquakes. In addition to detecting deformation before an eruption, we also see deformation immediately after an eruption, as was found at Westdahl and Okmok volcanoes in Alaska.
At other volcanoes, particularly calderas like Yellowstone, there may be up and down movement for hundreds or thousands of years without an eruption. Long Valley Caldera in Eastern California underwent several episodes of uplift in the 80s and 90s and the resurgent dome remains roughly 80 cm (31 inches) higher than it was in the late 1970's.
The Campi Flegrei caldera near Naples Italy had two episodes of uplift during 1970-1972 and again 1982-1984. The coastal town of Pozzuoli, within the caldera, was raised 170 cm (67 inches) and then 182 cm (72 inches) out of the ocean during those two intervals. Each time, some subsidence followed the uplift, but no volcanic eruption has occurred.
Probably the most astonishing example of volcanic uplift has been taking place on Iwo Jima, in the Volcano Islands, 1000 km S of Tokyo, Japan. The site of a critical WWII battle, Iwo Jima sits within a 4000 year-old caldera. Corals deposited on the ocean floor about 500 years ago are now found over 100 m (328 feet) above sea level. This requires uplift of the island of over 100 m (328 feet) within that short period of time. In addition, a shoreline landed upon by Captain Cook's surveying crew in 1779 is now 40 m (131 feet) above sea level. Clearly magma has accumulated a beneath the island, possibly as shallow as 2-3 km (1.6 miles), yet no eruption has occurred since the inflation began.
Two other examples of deforming volcanoes within the United States are at South Sister volcano in southern Oregon and Mount Peulik in the Aleutian Islands of Alaska. In each case, over 20 cm (8 inches) of uplift have been noted by InSAR during non-eruptive periods, presumably indicating some intrusion of magma beneath the volcanoes. Though future eruptions associated with these intrusions are possible, they are not required.
Clearly, deformation on volcanoes is a complicated process. Satellite-based technologies such as GPS and InSAR provide exciting new insight into the relationship between deep magmatic intrusion, ground movement and eruption processes. The coming years should provide more data and increase our ability to interpret ground movements of volcanic terrain.
Is it true that volcanic activity at Yellowstone has recently increased?
No. The volcanic system in Yellowstone National Park is displaying the same general types of restless activity today as it has since volcanic activity was first analyzed more than 50 years ago. Current behavior includes extensive seismicity, periods of uplift and subsidence of the caldera related to the movements of hydrothermal fluids that are produced and maintained by deeper magma beneath the Park, and intermittent changes to hydrothermal features at the surface.
What is the current status of volcanic activity at Yellowstone?
The monitoring update has information about the latest volcanic activity at Yellowstone.
