They are fast-moving fluidized bodies of hot gas, ash and rock (collectively known as tephra) which can travel away from the vent at up to 150 km/h.Source
The gas is usually at a temperature of 100-800 degrees Celsius.
The flows normally hug the ground and travel downhill under gravity, their speed depending upon the gradient of the slope and the size of the flow.
Most flows are around one to ten cubic kilometres and travel for several kilometres.
Mount Pinatubo Eruption
The greatest thickness of ash deposited 33 centimeters (13 inches) approximately 10.5 km (6.5 mi) southwest of the volcano.
From the Philippines in 1991 to NYC in 2001:
“There was so much of it. Everywhere, everything from there was ash. You have to wonder what they ended up doing with all of it after they were done sifting through it.”Bobbi Lawnichak, Red Cross volunteer at the WTC attacks.
Lawnichak said inspectors working around-the-clock first performed visual inspections of all the material brought to the landfill looking for clues before the material was sent through a series of screens from large to smaller and smaller before what remained were piles of fine gray ash.
Because of the sensitive nature of the work being performed, the Lawnichaks, as well as other volunteers, were prohibited from taking any pictures at either Ground Zero or the Staten Island landfill.
Were the government agents looking for 'clues' or gathering up and hiding evidence of the FALSE FLAG/INSIDE JOB of 9/11?
The video 911 Mysteries - Demolitions was released as a DVD in late 2006, and received acclaim from respected 9/11 Truth activists.911 Mysteries- Demolitions(part1)
0:39:04: As the buildings fell, they darkened Manhattan, filling the air with billowing clouds of dust and ash. What produces these huge, scudding cauliflower-like masses of slowly moving dust?
911 Mysteries narrator: "The US Geological Survey website provides us with a definition of a pyroclastic flow as a ground-hugging avalanche of hot gas and debris. The rising gas chimney is clearly visible in this photo of the North Tower implosion, with pyroclastic flows between buildings. The cauliflower shape of the debris cloud is a telltale sign of pyroclastic flows generated by massive explosions, typical of volcanic eruptions and controlled demolitions."
This film has 90 minutes of pure demolition evidence and analysis, laced with staggering witness testimonials. Moving from "the myth" through "the analysis" and into "the players," careful deconstruction of the official story set right alongside clean, clear science. The 9/11 picture is not one of politics or nationalism or loyalty, but one of strict and simple physics. How do you get a 10-second 110-story pancake collapse?
Now you can sift thru the evidence, use your brain, if it hasn't already been infected with the dreaded disease called 'Zionism' and make your own call on what really happened on 9/11.
If you still want to believe what the government shills have been pushing into American minds like some addictive drug, then that's your right, but for myself, I'll stick with my theory that 9/11 was a FALSE FLAG/INSIDE JOB.