Relationship between crater size and ejecta volume of recent magmatic and phreato‐magmatic eruptions: Implications for energy partitioning

Abstract

Relationships between crater diameter (D in meters) and ejecta volume (V in cubic meters) of recent magmatic and phreato‐magmatic eruptions are expressed as D=0.11 V 0.42 , and D=0.97 V 0.36 , respectively. Crater diameters of phreato‐magmatic eruptions are ca. 2–5 times larger than those of magmatic eruptions of similar ejecta volume, suggesting that magma‐water interaction in phreato‐magmatic eruptions generated mechanical energies of crater formation 1–2 orders of magnitude larger than equivalent‐volume magmatic eruptions. The conversion ratio of thermal energy to kinetic energy in phreato‐magmatic eruptions is estimated to be 0.7–10 percent, which is in accord with the presently available data of laboratory experiments on melt‐water interaction [ Wohletz and McQueen , 1984].