Volcanoes are the most dangerous things on Earth. Everything else I have seen listed is something that could cause a massive catastrophe. Volcanoes have caused massive, extinction-level events and they will again. Let me quote Wikipedia:
One proposed volcanic winter happened c. 70,000 years ago following the supereruption of Lake Toba on Sumatra island in Indonesia. According to the Toba catastrophe theory to which some anthropologists and archaeologists subscribe, it had global consequences,  killing most humans then alive and creating a population bottleneck that affected the genetic inheritance of all humans today…
It has been suggested that volcanic activity caused or contributed to the End-Ordovician, Permian-Triassic, Late Devonian mass extinctions, and possibly others. The massive eruptive event which formed the Siberian Traps, one of the largest known volcanic events of the last 500 million years of Earth's geological history, continued for a million years and is considered to be the likely cause of the "Great Dying" about 250 million years ago.
That is a series of numbers that are so large your brain is tempted to give up even trying to comprehend the scale… and it gets even crazier when you look at specific massive eruptions.
Let’s take the biggest eruption in the last 10,000 years, Tambora. This thing’s eruption was so loud that people 1600 miles away reported hearing the sound of guns firing. It shot 10 billion tonnes of matter into the air and caused ash to fall from the sky over 810 miles away from the site of the eruption.
What about beyond 10,000 years ago? Let’s take a trip to Yellowstone. Yellowstone is not just a fun park to visit, it is also a supervolcano that has erupted multiple times and each time it was gigantic. The largest occurred some 2.1 million years ago and was 2,500 times larger than Mount St. Helens. This eruption created the Huckleberry Ridge Tuft.
None of this mentions the atmospheric fallout effects that can last for centuries, the tidal waves, or the magma which just keeps flowing and flowing after these eruptions.
And if all that’s not real enough for you, just take a look at any picture from Pompeii.
I’d much rather take my chances with the mosquitos and H-bombs… we might be able to stop those. If a super volcano erupts, all we could do is pray.
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