The volcanic morphologies, and the maar-diatreme crater structures in particular, are fairly well preserved. The overall sequence shows that the initial crater-forming explosions were followed by strombolian activity. The San Venanzo eruptions caused progressive widening and deepening of the craters, which remained set in the sedimentary substratum. The initial products of San Venanzo volcano consist of breccias containing large accessory-blocks coming from the sedimentary substratum.
Late products consist of mainly lapilli-sized juvenile deposits.
Pyroclastic surge and minor pyroclastic flow are the main depositional mechanisms.