A supervolcano eruption destroyed the Roman city of Pompeii, near the coast of the Bay of Naples, in 79 A.D. Now it seems that a repeat is on the way: http://collapse.news/2017-02-07-report-supervolcano-that-could-kill-millions-of-europeans-ready-to-blow.html.The supervolcano is called Campi Flegrei, and is under Naples in Italy. There have been recent seismic signs that the volcano is reawakening and a big eruption will kill millions of Europeans. Clouds of ash could black out the sun, making Europe dark for years, if not a decade. Air travel, probably across the world, at least involving jets, would cease. Media reports say that the eruption could accelerate global warming, which is the religious faith. Actually volcanic eruptions contribute to global cooling, and a volcanic winter would be more of a concern than any hypothetical global warming: https://en.wikipedia.org/wiki/Volcanic_winter.
This has happened in the past. The Lake Toba supervolcano in Indonesia erupted around 74,000 years ago and wiped out over two thirds of the humans existing at the time. Global temperatures dropped 10 C for over a decade : https://www.theregister.co.uk/2014/01/06/scientists_discover_the_trigger_that_could_set_off_a_supervolcano/.
A more substantial eruption would have an absolutely devastating effect on the modern world, which is more vulnerable than most comfortably living city folk realize: http://www.academia.edu/21332548/Volcanic_eruptions_and_human_vulnerability_in_traditional_societies_past_and_present_Towards_a_palaeosocial_volcanology.
Professor Bill McGuire, a volcanologist and Benfield Professor of Geophysical Hazards at University College London and Director of the University’s Benfield Hazard Research Centre, says in his book, Surviving Armageddon, (Oxford University Press, Oxford, 2005), that technology is only able to predict a volcanic eruption, not stop it. He discusses the usual scenario of “nuking” it, as well as a hypothetical use of nanobots to dig away and release, more slowly the pressure, and says that such schemes “ignore the unimaginable energies locked up in these overwhelming natural phenomenon…exploding nukes and burrowing bots will bare about the same effect on a giant magna reservoir as a mosquito probing an elephant’s hide.” (p.p. 127-128)
McGuire also mentions the ultra-dangerous mass of rock on the western flank of La Palma’s Cumbre Vieja volcano: “this colossal mass of rock threatens to plunge into the adjacent ocean, generating (a) catastrophic tsunami capable of unprecedented destruction and loss of life around the entire North Atlantic rim.” (pp. 128-129) In 1949, this mass of rock, as large as the UK’s Isle of Man, dropped 4 metres closer to the sea. It is thought to be inexorably moving to the sea, set to doom much of coastal civilisation in the region: https://www.thesun.co.uk/news/1915593/tenerifes-mount-teide-volcano-threat-gives-chilling-reminder-of-nearby-la-palmas-cumbre-vieja-which-could-cause-mega-tsunami-when-it-next-erupts/.
I have a really bad feeling that it is only a matter of time before the human race’s phenomenal good luck, runs out.