Death Came Quickly to Those in the Path of the Pyroclastic

Death came quickly to those in the path of the pyroclastic flow that destroyed St.Pierre.Which of the following is not one of the possible causes?

A) Physical impact of the 190 km/h super-heated ash cloud
B) Inhaling the superhot gases
C) Burns from the hotter-than-700°C ash cloud
D) Burns from the low-viscosity lava that flowed rapidly down the volcano's slope and buried the city in a matter of minutes