'Hole in the clouds' in the Sarychev Peak eruption

Question

One of my favourite ever pictures taken from space is a picture of the 2009 eruption of Sarychev Peak (Ostrov Matua island, Japan) taken by an ISS astronaut during a lucky fly-over.

^{Image Source: Earth Observatory Image of the Day. I heartily recommend clicking through and seeing the animation.}

I always assumed that the hole in the cloud cover around the island was caused by some sort of shockwave originating in the eruption plume, most probably as a result of increased temperatures evaporating the cloud, or some such. However, upon revisiting the IOTD page, I was surprised to learn that this is not necessarily the case and that the origin of this hole is a matter of some controversy:

**Editor’s note: Following the publication of this photograph, the atmospheric and volcanic features it captured generated debate among meteorologists, geoscientists, and volcanologists who viewed it. Post-publication, scientists have proposed—and disagreed about—three possible explanations for the hole in the cloud deck above the volcano.

One explanation is that the hole in the clouds has nothing to do with the eruption at all. In places where islands are surrounded by oceans with cool surface temperatures, it is common for a sheet of clouds to form and drift with the low-level winds. When the cloud layer encounters an island, the moist air closer to the surface is forced upward. Because the air above the marine layer is dry, the clouds evaporate, leaving a hole in the cloud deck. These openings, or wakes, in the clouds can extend far downwind of the island, sometimes wrapping into swirling eddies called von Karman vortices.

The other two possibilities that scientists have offered appeared in the original caption. One is that the shockwave from the eruption shoved up the overlying atmosphere and disturbed the cloud deck, either making a hole or widening an existing opening. The final possibility is that as the plume rises, air flows down around the sides like water flowing off the back of a surfacing dolphin. As air sinks, it tends to warm; clouds in the air evaporate.

Has this controversy been settled? Is there a convincing, accepted explanation for the origin of the hole in the cloud cover?

Answer 1

This is a part answer, as it seems that the controversy is still current, due in no small part to the fact that no one was on the ground or nearby to obtain a side on view of the eruption. However, having said that, there are a few images of other volcanoes and similar weather phenomena to consider.

Note: this is not an attempt to fully answer the controversy.

Hole in the clouds or sometimes referred to as 'hole-punch clouds' such as the one below, observed in Mobile, USA:

According to the image source NOAA's page Unusual Cloud Structure Witnessed by Thousands, the formation of hole punch clouds is largely postulated to be due to

very small supercooled liquid water droplets can exist well below freezing (as low as -40 degrees (C, or Centrigrade) ). The temperature in the cloud layer was around -24 deg (C) at the time of occurrence. Sometimes...when ice and the supercooled liquid droplets coexist within a cloud...a process occurs whereby ice crystals grow at the expense of the droplets. If the mixed cloud is agitated...the supercooled droplets freeze instantaneously.

forming a 'hole' in the cloud. The key here is the the blast from the volcano could have provided the agitation needed for this process, as could the updraft from the island (mentioned in the quote in the question).

Other explosive volcanic eruptions interacting with clouds - a great example of this is the webcam image of an eruption of Popocatépetl is Mexico included in the article Webcam Captures Volcano Explosion and Shockwave in a Time-Lapse Video (Zhang, 2013), the stills from the webcam image is below:

Although there are some movement due to the shockwave in the very initial stage of the eruption, this occurred closer to the crater, and does not appear to affect the nearby clouds higher up.

Another example of an explosive eruption is Mt. Pinatubo, take a look at the image below of the early stages of the eruption, notice the clouds surrounding seem to be undisturbed, though, it is hard to say what is happening nearer to the eruptive column.

Image source