MORPHOLOGY, ERUPTION RATES, AND RHEOLOGY OF LAVA DOMES - INSIGHTS FROM LABORATORY MODELS

The growth of lava domes can be either quiescent or violent, with tran sitions between styles of behavior commonly occurring with little warn ing. Here we propose that the behavior depends on the eruption rate, t he magma rheology, and the thickness of the cooling surface. We presen t a model, based on laboratory simulations, field measurements, and ph otographic analysis, that relates the morphology and texture of a dome to the thickness of its cooled carapace, and thence to eruption condi tions. A sequence of four main types of dome (spiny, lobate, platy, an d axisymmetric) is identified in laboratory analog experiments with a Bingham plastic. These regimes are associated with progressively highe r effusion rates, lower cooling rates, lower yield strengths, and (in real lava flows) decreasing tendency for explosive decompression durin g flow front collapse and are ordered according to the value of a sing le dimensionless number. The model allows an estimate of the yield str engths of the magma forming active domes based on data for the effusio n rate and composition. It also permits the eruption rates of prehisto ric or extraterrestrial lava domes and flows to be appraised from thei r morphology, if their compositions can be estimated. A comparison wit h the laboratory results suggests that the Venusian ''pancake domes'' are likely to have basaltic to basaltic andesitic composition.