Questions About Monitoring Yellowstone

What are the main monitoring instruments of the Yellowstone Volcano Observatory?

Activity leading to a possibly impending volcanic eruption, hydrothermal event, 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.

How are Yellowstone earthquakes analyzed?

The University of Utah (UU) plots earthquakes in the Yellowstone area automatically on a map. In addition to the map, there are webicorder (seismogram) displays, also available from UU. The map and webicorders can be reached through the Yellowstone earthquake activity page. It was noticed during the Yellowstone Lake swarm that there were very small earthquakes visible on the webicorders that did not show up on the map.

There can be a delay in plotting the smaller earthquakes on the map.

Earthquakes with magnitudes greater than 1.5 (change from 2.5 occurred on October 1, 2010) are automatically located and then automatically plotted on the map. The smaller events must be analyzed by a seismic analyst to determine what are correct earthquakes from that area. Because the smaller events need to be individually located by a separate computer program from the automated system, they are added to the map later than those that are automatically located. The delay in reporting the smaller earthquakes is usually not very noticeable, except when there are large numbers of very small earthquakes.

Occasionally earthquake locations and magnitudes are found to be in error and are deleted or updated with improved information after being reviewed by a seismologist.

Only one week of earthquake data are plotted on the map.

The UU and USGS earthquake sites only plot the last week of data on the maps. That means that each day, one day of earthquakes will be erased from the map.

The data are available for you to view.

If you want to see all the data, you can access the located earthquake data from the University of Utah Seismograph Station archive of Yellowstone National Park Region Earthquake Listings. Also because the University of Utah is part of the Advanced National Seismic System (ANSS) all of its data are archived at the Data Management Center from which they can be downloaded. Also the earthquakes listings can be download from the USGS National Earthquake Information Center (NEIC) archive. The hypocenters (located earthquakes) we publish on the web site are not the "raw" data.

If you want to see what "raw" data, or waveforms look like, you can find them through the IRIS consortium. To make sense of the data you will need to do your own "picking" to locate earthquakes.

The calculations to determine the Yellowstone hypocenters are done by the University of Utah (UU). The UU is part of the ANSS run through the USGS earthquake program, and they follow the protocols set by the national seismic community.

To learn more about how earthquakes are measured we recommend starting with the USGS Earthquake Hazards Program FAQ on measuring earthquakes.

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 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 or hydrothermal fluids 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. Also stress changes on active faults can cause ground deformation that can be detected by GPS and InSAR methods.

There are a variety of techniques that can be used to monitor ground deformation. The earliest measurements of ground deformation in Yellowstone used precise surveying of elevation changes. This method is accurate to a few millimeters but did not provide horizontal measurement of ground motions. Electronic distance measurements (EDM, an instrument that both sends and receives an electromagnetic signal) were later used to determine both 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 only once or twice per year and take time to acquire and process. InSAR's great advantage 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. For example, 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 movements for tens to 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. Nonetheless the pronounced subsidence and uplift episodes of the Yellowstone caldera are closely monitored to discriminate between long-term periods of unrest from impending volcanic eruptions and large earthquakes.

What is the normal volcanic activity level for Yellowstone?

The volcanic system in Yellowstone National Park has displayed similar behavior since volcanic activity was first analyzed more than 50 years ago. By analyzing the activity over time, we gain a better understanding about what is background or normal activity. Different volcanoes have different levels of normal activity. Normal activity for Yellowstone includes extensive seismicity, periods of uplift and subsidence of the caldera, and intermittent changes to hydrothermal features at the surface. There are usually over a thousand earthquakes per year at Yellowstone. About 40% of the earthquakes every year are associated with swarms. The beautiful hydrothermal features in the park (geysers, hot springs, mud pots, etc.), the uplift and subsidence, and many of the earthquakes are caused by the movements of hydrothermal and/or magmatic fluids. The hydrothermal fluids are produced and maintained by the partially liquid magma chamber beneath the Park (see the questions and answers regarding research at Yellowstone for more information).

What is the current status of volcanic activity at Yellowstone?

The current status of volcanic activity at Yellowstone can be found in the Yellowstone Volcano Observatory's monitoring update. The update is written once a month. Additional updates are written for less frequent activity such as a large earthquake or earthquake swarm. The monitoring page also includes access to the near real-time data.