eruption The release of lava and gas from the Earth's interior on to the Earth's surface and into the atmosphere. Where the gas component is minimal (e.g. in basaltic magma) lava is released quietly; where the gas component is large (e.g. in rhyolite magma) lava is explosively fragmented by the expanding gas as it is released, forming high eruption columns of ash and pumice above the vent. Such contrasts in the explosivity of eruptions have been used to define several eruption styles, ranging from the quiet Hawaiian type to the violently explosive Phreatoplinian type.

eruption XV. — (O)F. éruption or L. ēruptio, -ōn-, f. ērumpere, ērupt- burst forth, f. E- + rumpere break; see -TION.
So erupt, eruptive XVII.

eruption (i-rup-shŏn) n.
1. the outbreak of a rash.

2. (in dentistry) the emergence of a growing tooth from the gum into the mouth.