Answer to Question 1
C
Answer to Question 2
Pyroclastic flows consist of hot gases infused with incandescent ash and larger lava fragments. Also referred to as nue ardentes, these fiery flows are capable of racing down steep volcanic slopes at speeds that can exceed 100 kilometers per hour. Pyroclastic flows are propelled by the force of gravity and tend to move in a manner similar to snow avalanches. They are mobilized by expanding volcanic gases released from the lava fragments and by the expansion of heated air that is overtaken and trapped in the moving front. These gases reduce friction between ash and pumice fragments, which gravity propels downslope in a nearly frictionless environment. This accounts for the reason some pyroclastic flow deposits are found many miles from their source.