Eruption source parameters - how are they defined?

Each volcano is assigned an eruption type (e.g. MO see Table 1) subjectively based on its historical behaviour (or lack thereof), using the guidelines presented in in Mastin et al., [2009a] and summarised here and in Table 1.

At volcanoes where the magma type of recent eruptions is known, an eruption type "M" (mafic; for example, basalt or similar low viscosity magma) or "S" (silicic; for example, andesite, dacite, rhyolite, or other higher viscosity magma) is assigned.

For a given explosive eruption size as measured by plume height or erupted tephra volume, mafic and silicic eruptions typically display somewhat different durations and grain-size distributions and so are assigned slightly different source parameters in the classification scheme.

If the magma type is unknown or inaccessible, we assign it on the basis of the type of volcanic feature in the Smithsonian Institution database [Siebert and Simkin, 2002-9]. For example, shield volcanoes, fissure vents, cinder cones, and maars are considered mafic; whereas stratovolcanoes, lava domes, pumice cones, calderas, complex volcanoes, explosion craters, and bimodal volcanic fields are considered silicic.

For volcanoes with enough well-described historical eruptions to discern a trend, we assign future eruption type based on the range in plume height of observed eruptions (where available) or on the most common eruption size as listed in the Smithsonian Institution database, using the volcanic explosivity index (VEI) of Newhall and Self [1982].

For volcanoes that have erupted many times since 1900AD, particular weight is given to eruptions in the past few decades in assigning an eruption type. Volcanoes with no well-described historical activity are assigned default type M0 or S0, and volcanoes whose vents lie more than 50 m below the ocean surface are assigned type U0, which is assumed to produce no eruptive plume.

All those volcanoes that have had historical eruptions are highlighted in the database, using information from the Global Volcanism Program, Smithsonian Institute. Volcanoes that are ice-covered are also highlighted, using information from Hobbs et al. (2014).

Type Magma type Historical eruption characteristics Example
(date M/D/Y)
Htkm above vent D hr M kg/s V km3 m63
M0 Basalt or other mafic Insufficient historical data to characterize Cerro Negro, Nicaragua,
7 60 1 x 105 0.01 0.05
M1 H ≤ 5 km or VEI ≤ 2 Mount Etna, Italy,
2 100 5 x 103 0.001 0.02
M2 H = 5–8 km or VEI = 3 Cerro Negro, Nicaragua,
7 60 1 x 105 0.01 0.05
M3 H > 8 km or VEI ≥ 4 Fuego, Guatemala,
10 5 1 x 106 0.17 0.1
S0 Andesite, dacite, rhyolite, or other silicic composition Insufficient historical data to characterize Mount Spurr, USA,
11 3 4 x 106 0.015 0.4
S1 H ≤ 6 km or VEI ≤ 2 Mount Ruapehu, New Zealand,
5 12 2 x 105 0.003 0.1
S2 H = 6–12 km or VEI = 3 Mount Spurr, USA,
11 3 4 x 106 0.015 0.4
S3 H ≥ 12 km or VEI ≥ 4 Mount St. Helens, USA,
15 8 1 x 107 0.15 0.5
S8 Major pyroclastic flows, with an elutriated column rising primarily above the flows. Mount St. Helens, USA,
5/18/1980 (pre-9 AM)
25 0.5 1 x 108 0.05 0.5
S9 Active lava dome is present Soufrière Hills, Montserrat (composite) 10 0.01 3 x 106 0.0003 0.6
U10 All magma types Submarine vent with a water depth ≥ 50 m None 0 - - - -

Uncertainty in assigned eruption source parameters

These examples represent our best assessment of the typical type and size of future explosive eruptions, but actual eruptions will vary from these examples. These parameters are for use before actual observations of an eruption are available (e.g. during unrest) to support planning and preparation. To account for the possible range of values, modellers should consider running multiple scenarios, such as the following:

  1. Run forecasts for eruption types M1, M2, and M3 or for eruption types S1, S2, and S3 simultaneously, depending on the volcano's magma type.
  2. For type S9 volcanoes, run models S1, S2, S3, and S9.
  3. For type U0 volcanoes, run models for eruption types M1 and M2.
  4. As observations are acquired during an eruption, some scenarios can be eliminated, and others refined.


The information contained on this site concerning eruption source parameters is a combination of data and records from a wide variety of resources from around the world. It is provided "as is" and without any warranty or condition express or implied, statutory or otherwise as to its quality or fitness for purposes. Users therefore download and use the information purely at the own risk. All conditions, warranties, terms and undertakings express or implied or otherwise in respect of the data/information are hereby excluded to the fullest extent permitted by law.


Mastin, L G, et al. 2009a. A multidisciplinary effort to assign realistic source parameters to models of volcanic ash-cloud transport and dispersion during eruptions, J. Volcanol. Geotherm. Res., 186(1–2), 10–21,

Mastin, L G, Guffanti, M, Ewert, J W, and Spiegel, J. 2009b. Spreadsheet of eruption source parameters for active volcanoes of the world, in US Geological Survey open-file report 2009–1133, edited, p. 6.

Neal, C A, McGimsey, R G, Gardner, C A, Harbin, M L, and Nye,C J. 1995. Tephra-fall deposits from the 1992 eruptions of Crater Peak, Mount Spurr, Alaska, in The 1992 eruptions of Crater Peak, Mount Spurr, Alaska, USGS Bulletin 2139, edited by T E C Keith, pp. 65–79, US Geological Survey, Washington, D C.

Hobbs, L K. 1995. The role of cold supraglacial volcanic deposits in influencing glacial ablation. PhD thesis, Lancaster University, UK.

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