Monitoring:  | Gas | Ground Deformation | Hydrologic | Remote Sensing | Seismicity |

How much sulfur dioxide gas is released into the atmosphere during an explosive eruption?

Until scientists discovered that the total ozone mapping spectrometer (TOMS) sensor sent aloft in 1979 could be used to map the distribution of sulfur dioxide gas in the stratosphere, there was no way to know. The first TOMS sensors aboard the Nimbus-7 and Meteor-3 satellites detected 55 out of 350 known eruptions between 1979 and 1992, and also from several eruptions not known from ground studies. These early TOMS instruments could only measure the presence of sulfur dioxide gas from moderate to large eruptions that spread eruption clouds over enormous areas. Improved TOMS instruments on satellites launched in 1997 into lower orbits, however, are detecting sulfur dioxide gas from smaller eruptions and from the passive degassing of some volcanoes.

The TOMS sensor was designed to quantify the amount of ozone in upper levels of the Earth's atmosphere by measuring the amount of sunlight which is scattered back to the satellite compared to how much is incoming. Absorption of energy at six wavelengths is measured and used to estimate the total amount of ozone. Following the eruption of El Chichón in 1982, scientists noticed anomalously high values of ozone over Mexico. Subsequent research found that sulfur dioxide also absorbed energy at some of the same wavelengths as ozone, and a mathematical algorithm was developed for TOMS to measure the amount of sulfur dioxide gas released by volcanoes.

Map shows the location of Mount Spurr and its eruption cloud of sulfur dioxide gas about 15 hours after the volcano stopped erupting on August 18, 1992. Scientists estimated the eruption cloud contained about 240,000 metric tonnes of sulfur dioxide, spread over 370,000 km2. The amount of sulfur dioxide in the above image is shown in Dobson Units, which is the thickness of pure sulfur dioxide gas in centimeters, if the gas was brought down to standard temperature and atmospheric pressure.

More information about TOMS

TOMS volcanic sulfur dioxide and ash

This Web site describes the methodology and research performed by the TOMS SO₂ and Ash Group, based at the NASA Goddard Space Flight Center to detect, track and measure volcanic eruption plumes from space.

Total ozone mapping spectrometer inventory

Follow volcanic clouds in near real time with TOMS. This Web page shows both sulfur dioxide and aerosol index data. The sulfur dioxide signal is specific to volcanic clouds. The aerosol index will locate all absorbing aerosol clouds, which include volcanic ash clouds, dust, and smoke clouds.

Total ozone mapping spectrometer inventory

Website for information, data, and images from the Total Ozone Mapping Spectrometer (TOMS) instruments.

Other applications of volcano monitoring using satellites

• Detecting Eruption Clouds with Weather Satellites
• Detecting Thermal Features of Volcanoes