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No. Block lava is low-moving viscous lava, usually of andesitic or similar composition. A pyroclastic flow is a very fast-moving mixture of hot ash, rock and gas.
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Does mt st helens have pyroclastic flow?
No. It has a crater, which is not quite the same as a caldera.
Is a pyroclastic flow the same as an ash cloud?
No. The term ash cloud typically refers to the plume of ash and gas that rises above an erupting volcano. A pyroclastic flow is a denser mass that hugs the ground.
What is the difference between lava flow lava fountains and lava tubes?
A lava flow is basically a stream of lava on the surface. A lava tube is an underground cave through which lava flows downhill. A lava fountain is lava shooting into the air out of a volcano in much the same manner as a water fountain.
Why is a lava flow such a big problem when they could just freeze it?
That is easier said than done. The amount of water required too cool a lava flow would have to have a volume on the same order of magnetude as that of the flow itself. In most cases it is not reasonable to move this much water. Spraying a lava flow with water will form a crust that hels insulate it from further cooling. The lava will then breath through the crust again.
Are all lava flows the same?
No. Lava flows vary in composition. Most lava flows consist of basaltic lava, which can flow as smooth phoehoe or form jagged and broken a'a. Other lava flows are more viscous and will have blocky surfaces and tend to be short and thick.
How are pyroclastic flows formed?
There are a number of ways in which pyroclastic flows occur and the first follows a Plinian eruption. If a fountain collapse of its eruption column occurs the jet is not able to heat the air sufficiently and lack of convection causes the plume to fall rather than shoot upward and flow down the mountain. The second is the same type of collapse after a vulcanian eruption in which a gas cloud is created that is denser than the air around it and this turns into a pyroclastic low. Other ways include a lava dome suffering a gravitational collapse, the mouth of a vent in a volcano frothing when the erupted lava degasses and when a section of a volcano collapses and a directional burst occurs.
Is molten rock and lava flow the same thing?
Not exactly. Molten rock is called either magma or lava depending on whether it is underground or above ground. When lava flows on the surface like a river or flood it is called a lava flows, but lava is not always flowing downhill. Sometimes it can collect in a pool called a lava lake, or be flung into the air in a lava fountain.
Does mt st Helens have pahoehoe or AA lava?
Niether. Pahoehoe and a'a are both varieties of basaltic lava. The material from Pinatobo is of a dacitic composition, which is much more viscous than a'a or pahoehoe. It tends to erupt explosively, producing ash and pumice rather than lava flows. When dacitic lava does flow it creates a block lava flow.
Can welded and cemented tuff result from same volcano?
Yes. A welded tuff may form from pyroclastic flow deposits near the volcano with cemented tuff farther away or resulting from a different eruption.
Does all lava flow at the same speed?
No. The fastest lava flows on earth have been recorded at Mount Nyiragongo in the Congo flowing at 60 mph (100 km/h). In most cases, however, lava flows very slowly. Blocky lava flows are the slowest, moving at speeds comparable to glaciers.
Can lava kill you if you are underwater?
You can die if you do not get away quickly. The radiant heat from a lava flow, especially a basaltic lava flow, is very intense. Being close to a large flow without protection can quickly kill a person. Fortunately, these flows are slow moving, and the same radiated heat will often make it unbearable to get any closer before you could get close enough for it to kill you.
Can demolition explosions cause pyroclastic clouds?
No. The dust clouds produced by the demolition of a building may visibly resemble pyroclastic flows, but they are not the same thing.
