Actually, what he’s calling “Novarupta” is only the dome plug that blocked off the volcano’s main vent at the end of the eruption. The volcano itself, I believe, is a fissure that may have underground magma connections to Katmai and perhaps other nearby volcanoes.
This volcano’s complex details are sometimes hidden, but Novarupta’s 1912 blast was impossible to miss – an ultra-plinian eruption on a scale comparable to the 19th century eruption of Krakatoa.
As with Italy’s Campi Flegrei, you have to go out into space to get the whole picture.
That dome plug (“Novarupta Dome”) looks pretty small in the wide view, doesn’t it?
Note the big lake east of the dome. That’s Mount Katmai, which collapsed in on itself during the eruption, forming a caldera that Erik Klemetti describes as “one of the biggest red herrings in the history of geology.”
On June 5, 1912, the landscape above would have looked very different and more typical, say, of Denali National Park in summer.
Katmai would have been a big, fairly pointy-topped, white mountain like all the others.
There would possibly have been a cluster of smaller, snow-covered mountains, I think, west of Katmai, where the Novarupta dome and lots of gray-brown ash are now seen in the above AVO image.
If so, these small mountains probably resembled the current cluster (PDF), including Trident and Mageik volcanoes, that still stands near Katmai to the southwest.
We’ll never know for sure now.
June 6, 1912
Immediately after the eruption, once researchers could get into the area, they noticed that the top of Mount Katmai had collapsed and so assumed, reasonably, that it had been the source of the eruption and of the new, steaming and thick sheet of ash that now was called the Valley of Ten Thousand Smokes.
Here is what that valley looked like five years after the eruption:
I understand you could still cook eggs and boil water there in the 1980s, but all in all, the huge ash sheet has cooled quite a bit over time.
Anyway, in the 1970s, scientists noticed that the ash actually gets thicker as you move away from Katmai, so that volcano couldn’t have been the source for the 1912 eruption. Rather, they learned, it had come from an entirely new vent near the base of Mount Trident.
Katmai had collapsed, according to some scientists, because of the very complex underground magma network that fed this massive eruption. (Klemetti, 2012)
However, this volcanic complex’s “plumbing” is still quite poorly understood.
In any event, the 1912 eruption blew out nearly seven cubic miles of material in 60 hours, with roughly two-thirds of it going into the air and the rest scouring the surface as pyroclastic density currents (Oppenheimer, 2011)
Amazingly, no one that we know of was killed, although the ash caused health problems for humans, especially in Kodiak. It also devastated wildlife and plants on land and in the waters nearby.
All of southern Alaska had ashfall, as did Dawson, Ketchikan, and even Puget Sound. Per the Alaska Volcano Observatory, “Volcanic dust and sulfurous aerosol were detected within days over Wisconsin and Virginia; within 2 weeks over California, Europe, and North Africa; and in latter-day ice cores recently drilled on the Greenland ice cap.”
However, the eruption’s global impact was surprisingly light, according to Erik Klemetti, probably due to timing and location. It just caused some cooler temperatures in the northern hemisphere and affected the atmosphere’s opacity (which has something to do with the greenhouse effect) as far away as Algeria.
Clive Oppenheimer notes that if this all had happened in December rather than June, there could have been a much more pronounced greenhouse effect.
More information: I’ve only covered a few of the high spots. There is a wealth of free information online, especially after the 2012 centennial of the eruption.
One of the earliest thorough and yet very readable accounts of this event is The Valley of Ten Thousand Smokes (1922) by Robert Fiske Griggs and the National Geographic Society.