Get close to a pyroclastic flow

Julio Cornejo of the Santiaguito Volcano Observatory, INSIVUMEH (Spanish), in Guatemala is probably no more suicidal than anyone else who chooses a career that constantly brings them close to erupting volcanoes.

However, he captured very close footage of a pyroclastic flow last month, giving the rest of us a view of something that people don’t usually survive seeing close up.

It was a very small flow, not a big one like these, but the material was still hundreds of degrees hot and powerful enough to break trees. Turn your speakers up – those background noises of moving rock and breaking trees are quite unnerving.

It’s really a masterful, if risky, piece of filming.

It also answers a question I have had ever since reading Volcano Cowboys, in which the author, a highly educated layman, says that pyroclastic flows move silently. Logically, I can accept this since they move on superheated air, but I have seen videos where there were clinking, clanking sounds and wondered. The things do carry big rocks sometimes, after all.

Well, this flow moves silently. It’s there before you realize it (the billowing clouds).

OK. Now I know.

Below the video here is an explanation as per poster Rudiger Escobar Wolf Rudiger Escobar Wolf – I don’t know who he is or what he does, but as we saw Friday, he has access to technology as well as cats. He also refers below to PDCs, as a good scientist would – these things really are pyroclastic density currents, since they are gravity driven. And, it is this video that’s linked at INSIVUMEH’s site.

¡Gracias! INSIVUMEH.
 


 

00:00 to 00:06
First slow moving PDC front comes into scene, moving from left to right on the opposite bottom part of the channel. There seems to be only a moderate amount of ash, and to some extent the overriding cloud seems to vanish in parts (maybe due to a large water vapor component?), although some ash clearly lingers in the air.

00:07 to 00:10
A similar PDC wave is seen following a similar path.

00:11 to 00:18
The clouds rapidly lift, possibly aided by convection, and perhaps dominated by gases (mainly water vapor and droplets) and with relatively low ash.

00:19 to 00:24
A similar PDC wave comes across the scene in the center of the channel. The PDC is carrying logs and depositing them in this scene. The cloud of ash and gases/vapor doesn’t dissipate that quickly and remains over the area.

00:25 to 00:30
A continuous PDC can be seen moving across the channel bottom, carrying more rocks and logs, which move relatively slow and seem to come to rest.

00:31 to 01:00
A series of PDC pulses seem to come across the area, producing an increase in ash and gases/vapor rising from the channel and obscuring the actual flow processes.

01:01 to 01:10
The ash rising from the PDCs increases dramatically, and the sound of crushed and uprooted trees and vegetation (and perhaps colliding blocks) becomes very intense.

01:11 to 01:14
A tree (~ 15 m tall), presumably at the slope of the channel wall, is repeatedly hit by the PDCs and violently taken down in a matter of ~ 2 seconds. The noise of crushed vegetation (and perhaps colliding blocks) remains very loud.

01:15 to 01:35
Dense ash clouds continue to rise from the PDCs in the channel, engulfing the vegetation close to the channel margin, but in some cases quickly moving away.

01:36 to 01:42
A tree (~ 15 m tall) on the left part of the screen is violently shaken by the PDCs in the channel (similar to what happens between 1:11 and 1:14).

01:43 to 01:49
The camera momentarily moves away from the tree being impacted by the PDCs

01:50 to 01:59
The camera focuses again on the tree being violently shaken by the PDCs.

02:00 to 02:02
The tree is rapidly crushed by the PDC, appearing to be “sucked in” by the flow (probably being snapped or uprooted and leveled by the lateral impact of the PDCs. This happens so quickly that some of the leaves remain suspended in the air for a vew fractions of a second, and then slowly fall into the channel.

02:03 to 02:36
Dense ash clouds rise repeatedly from the PDCs in the channel, but appear to also be partially sucked in by the complex air circulation near to channel margin (possibly influenced by the PDCs flow and the associated convection).

02:37 to 02:39
A smaller tree (~ 10 m tall) is quickly “sucked into” the channel by the PDCs, in a similar way to the tree in 2:00 to 2:02.

02:40 to 02:47
A group of birds (parrots?) can be heard in the background, probably escaping the area.

02:48 to 03:42
Thick ash clouds keep rising from the PDCs in the channel, but the noise of vegetation and tress being crashed subsides. The circulation of the ash clouds suggests complex convection patterns near the channel.

03:43 to 07:19
This part of the video shows the broader upwards convective circulation of the ash clouds, as they rise from the PDCs in the channel.



Categories: Sunday morning volcano

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