Pyroclastic fall

They exhibit mantle bedding—the deposits directly overlie pre-existing topography and maintain a uniform thickness over relatively short distances.

The distribution of pyroclastic ash depends largely on the direction of wind at intermediate and high altitudes between approximately 4.5 – 13 km.

The 1912 eruption in the Valley of Ten Thousand Smokes (Alaska) covered an area greater than 100,000 km2 to a depth of six mm.

Pyroclastic falls exhibit lateral and commonly vertical variations in the nature and size of fragments.

The 79 AD eruption of Mount Vesuvius[2] produced the Pompeii Pumice which is an example of lateral and vertical variations.

Pyroclastic fall layers of volcanic ash on Izu Oshima volcano in Japan. The ash fell on an uneven ground surface. The ash layers have not been folded after deposition.