Reddit reviews Eruptions that Shook the World

I believe there is a way to look at the volcanic ash and basically know everything there is to know about any particular eruption. Each volcano has a unique "fingerprint" in its ash deposits, and each eruption leaves its own signature in that ash.

It's likely that the researchers took samples from the ash deposit of 1707, which is buried in sediment (probably), and figured out how much pressure it must have taken to make that kind of ash, and how high it was sent up in the atmosphere, and how long it stayed in the air, etc etc.

Read "Eruptions that Shook the World" if you want to have your mind blown harder than Mt St. Helens.

By the way, I'm no geologist or volcanologist. I just read the book and kind of have an understanding of it.

I really like Horseshoe Crabs and Velvet Worms or any book by Richard Fortey, really if paleontology and the biological history of the earth is interesting to you.

Krakatoa: The Day the World Exploded is also great, especially if you like volcanoes. And sort of similarly is Eruptions that Shook the World.

I also second The Seashell on the Mountaintop that /u/ap0s suggested. It's very good!

One book I found particularly interesting was: Eruptions that shook the world by Oppenheimer https://www.amazon.co.uk/Eruptions-Shook-World-Clive-Oppenheimer/dp/0521641128
I am sure you can get it cheaper elsewhere, but it gives a good background to eruptions.