1The property of being explosive; the degree to which something is explosive.
2Volcanic activity characterized by the forceful ejection of pyroclastic material; the magnitude of such activity during an eruption or phase of an eruption; the property of erupting in this way.
explosivity/ˌɛkspləʊˈsɪvɪti/ /ˌɛkspləʊˈzɪvɪti/ /ɪkspləʊˈsɪvɪti/
Early 20th century; earliest use found in Journal of the American Chemical Society. From explosive + -ity, in sense 1 after German Explosivität.