The growth of lava domes can be either quiescent or violent, with transitions between styles of behavior commonly occurring with little warning. Here we propose that the behavior depends on the eruption rate, the magma rheology, and the thickness of the cooling surface. We present a model, based on laboratory simulations, field measurements, and photographic analysis, that relates the morphology and texture of a dome to the thickness of its cooled carapace, and thence to eruption conditions. A sequence of four main types of dome (spiny, lobate, platy, and axisymmetric) is identified in laboratory analog experiments with a Bingham plastic. These regimes are associated with progressively higher effusion rates, lower cooling rates, lower yield strengths, and (in real lava flows) decreasing tendency for explosive decompression during flow front collapse and are ordered according to the value of a single dimensionless number. The model allows an estimate of the yield strengths of the magma forming active domes based on data for the effusion rate and composition. It also permits the eruption rates of prehistoric or extraterrestrial lava domes and flows to be appraised from their morphology, if their compositions can be estimated. A comparison with the laboratory results suggests that the Venusian pancake domes are likely to have basaltic to basaltic andesitic composition. ¿ 1998 American Geophysical Union