On the genesis of ignimbrites how ignimbrites and other pyroclastic products originate from a flowing melt

All the textural and structural characteristics of the alkaline ignimbrites of Northern Latium have been studied in detail. The study clearly indicates that these «ignimbrites» are the products of differential gas exolution from gas-oversaturated melts during and after their moving on the surface. It was also found that the processes of differential gas expansion, depending on the initial melt viscosity, mechanical stresses, etc., result in the whole series of features recognised as typical of ignimbrites. A careful re-examination of the «classic» Italian acid calc-alkaline ignimbrites, and a critical review of analogous materials known from the international literature allowed the Authors to extend the genetic trend of the alkaline ignimbrites of Latium to all deposits having ignimbritic character, and to rearrange their broad range of variability into a comprehensive genetic picture.