base surge A turbulent, dilute flow of ash and either water or steam, which expands radially as a collar-like cloud from the base of a vertically venting eruption column generated by the explosive interaction of magma and water. The surges are commonly cold and wet, consisting of ash mixed with water at temperatures below 100°C. With a high magma : water mass ratio the surges can become dry and hot, consisting of ash mixed with steam. Base surges can be very hazardous, as was the one that occurred during the eruption of Taal, Philippines, 1965. Radially expanding basal clouds observed in nuclear explosions are a type of base surge. See SURGE.

base surge A turbulent, dilute flow of ash and either water or steam, which expands radially as a collar-like cloud from the base of a vertically venting volcanic eruption column generated by the explosive interaction of magma and water. The surges are commonly cold and wet, consisting of ash mixed with water at temperatures below 100°C. With a high magma: water mass ratio the surges can become dry and hot, consisting of ash mixed with steam. Base surges can be very hazardous, as was the one that occurred during the eruption of Taal, Philippines, 1965. Radially expanding basal clouds observed in nuclear explosions are a type of base surge.