Pyroclastic flow across the ocean.. method theory?

Question

Pyroclastic flow from violent volcanic eruptions is known to be able to traverse vast distances across the ocean. My theory is that this is achieved via an effect similar to pouring liquid nitrogen onto living tissue except in reverse... upon contact the extreme heat levels of the pyroclastic flow vapourise the surface water into super heated steam creating a cushion along which the flow can ride. Eventually this cools with progresion along the ocean surface leading to the termination point of the flow. At this point the effect is insufficient to support the flow and the volcanic cloud collapses into the ocean.

What do you volcano experts out there think? Fact or myth? If not true please suggest a more educated theory.

Pyroclastic flow from violent volcanic eruptions is known to be able to traverse vast distances across the ocean. My theory is that this is achieved via an effect similar to pouring liquid nitrogen onto living tissue except in reverse... upon contact the extreme heat levels of the pyroclastic flow vapourise the surface water into super heated steam creating a cushion along which the flow can ride. Eventually this cools with progresion along the ocean surface leading to the termination point of the flow. At this point the effect is insufficient to support the flow and the volcanic cloud collapses into the ocean.

What do you volcano experts out there think? Fact or myth? If not true please suggest a more educated theory.

NEW: Whats peoples thoughts on jimboites' magma degassing theory to create a cushion? Interesting point about traversing across the land as well..

Answer 1

I think you are correct. The pyroclastic flow, being a density-driven flow on land (sort of like a giant , hot, terrestial turbidite debris flow!) can ride over the ocean surface for considerable distances on a bed of super-heated steam. The precise distance being determined by the speed of the pyroclastic flow, its temperature, and the conditions of the ocean surface (one imagines a pyroclastic flow wouldnt't get so far over a stormy sea!).

Once the pyroclastic flow has cooled sufficiently, it stops generating steam and simply sinks to the sea-bed, forming a layer of marine tuff. Once on the sea-bed, and mixed in with sediment, it might however be quite difficult to differentiate from other types of marine tuff that have been derived by more conventional "airfall" means. But there might be geochemical and/or grainsize and grain character differences that could be used to discriminate (I don't know for sure, as I'm only a geologist, not a vulcanologist!).

I have only recently (i.e. within the last five years) heard of this theory, but I believe that it has been scientifically tested and proven on a small scale in the laboratory.

Answer 2

Sounds right to me. The behavior of hot pyroclastic flows when they interact with cold seawater has been a topic of great debate in the field of volcanology, largely because the process has rarely been observed. As a result of the Soufriere Hills eruption, this process was captured on video for the first time. A remarkable feature of this interaction is that part of the hot flow continues over the surface of the water. There is speculation that as a flow travels across the sea surface it is supported by a layer of steam that develops at its base, much like a hovercraft skimming over water at high speed. An extreme example of a pyroclastic flow travelling over water occurred during the great eruption of Krakatau volcano in Indonesia. On August 27, 1883, a large pyroclastic flow was generated during the eruption and part of the flow traveled over 40 kilometers of water to the coast of Sumatra, where the hot gases and particles killed more than 1,000 people.
Good picture at the second link!

Answer 3

Rivers flow into the ocean because water flows downhill, towards lower ground. See, there are these things called "mountains" that are really really tall, and so when the snow on the mountains melts, the water flows down the mountains, making rivers that flow into the ocean because of this other thing called "gravity." You know, any science book from first grade could have told you all this. Try reading something other than the Bible once in a while.

Answer 4

Although your idea sounds plausible, it is essentially wrong. Pyroclastic flows also occur over land where water may or may not be available. What really happens is that the magma degases, creating a "cushion" upon which the lava rides. This degassing event is what propels lava away from the volcano.

EDIT: This is not my "theory" but what I was taught when I took Mineralogy class. The fact that lava contains volatiles, and that those volatiles are released during eruptions, is common knowledge among geologists.

Answer 5

Vulcanologists determined through a number of studies over years that this is the actual way that pyroclastic flows can flow over ocean (and other water).
I don't have the date when it was published (I thought it was sometime around 1995 but that may be wrong).

Answer 6

I'm not a volcano expert but that sounds about right to me.

Answer 7

Your theory is correct and can be scientificly confirmed.

Keep on studying we can never learn too much.

Answer 8

i had exactly this conversation 3 days ago, we both came to your conclusion.

Answer 9

confusing step. try searching with yahoo or google. just that might help!