Magma mixing at the El Hierro submarine eruption The eruption
started from a submarine fissure system on 10 October extending
in a N-S direction in the submarine prolungation of El Hierro's
southern rift zone, beginning at about 6 km distance from La
Restinga at depth of 1000 m, until the closest vent at about 2
km distance and depth of ca. 300 m. Above the vents, floating
(still hot) scoria and bombs of up to 30 cm diamenter were first
observed and sampled on 15 Oct. The shape and texture of these
scoria, with quenched surfaces due to rapid cooling with sea
water, were similar to the scoria composing the cinder cones
dotting the rift zone on land. This suggests that the eruption
is a submarine equivalent of basaltic strombolian fissure
eruptions. The fragments were mainly black and of basanitic
composition, i.e. extremely poor in silica (even less than
basalt). They contain 43‐45% de SiO2 and about 2% of volatiles
(H2O, CO2, Cl, S, ...) and were erupted at temperatures around
1200 ºC. Their density was about