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).

Table 1. Guidelines used to assign eruption types to the world's volcanoes using the method of Mastin et al. 2009a. The symbol H indicates mode plume height of recent historical eruptions. We assume that the most likely future eruption will resemble past recent explosive eruptions. If both plume height and volcanic explosivity index (VEI) are available, the plume height that characterizes most eruptions at this volcano in recent decades is used to assign an eruption type. Eruption type S8 (elutriated ash column) is assigned to a volcano only during an eruption on the basis of whether large-scale pyroclastic flows are being produced, not on the basis of historical activity. Eruption types and source parameters assigned to each eruption type [the mass eruption rate M, erupted volume V, and mass fraction of fine ash m63 for each eruption type are based on mapping and characterization of the tephra-fall deposits at the example eruptions given in column 4. Plume height H and eruption duration D are from historical accounts of those example eruptions.]

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, 4/9–13/1992	7	60	1 x 105	0.01	0.05
M1		H ≤ 5 km or VEI ≤ 2	Mount Etna, Italy, 7/19–24/2001	2	100	5 x 103	0.001	0.02
M2		H = 5–8 km or VEI = 3	Cerro Negro, Nicaragua, 4/9–13/1992	7	60	1 x 105	0.01	0.05
M3		H > 8 km or VEI ≥ 4	Fuego, Guatemala, 10/14/1974	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, 8/18/1992	11	3	4 x 106	0.015	0.4
S1		H ≤ 6 km or VEI ≤ 2	Mount Ruapehu, New Zealand, 6/17/1996	5	12	2 x 105	0.003	0.1
S2		H = 6–12 km or VEI = 3	Mount Spurr, USA, 8/18/1992	11	3	4 x 106	0.015	0.4
S3		H ≥ 12 km or VEI ≥ 4	Mount St. Helens, USA, 5/18/1980	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.

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