Neanderthals sang like sopranos
http://www.abc.net.au/science/news/stories/s1323798.htm
“all the volcanoes apparently erupted around the same time” apparently refers to several European volcanos, but the time period is geological not linear. Exact dates are not known: the eruptions may have been separated by hundreds or thousands of years, and neither is the all important question of eruption duration known.
So take this theory with a huge dose of NaCl.
Mt. Vesuvius has a huge caldera which may represent a huge blowout around 25,000 years ago. Sakura-jima in Japan blew a 15 mile diameter crater around 22,000 years ago. Several such events would have further decimated Neanderthal/human populations, especially if they had also been reduced by events 40,000 years ago. Lots more here to study and undersatnd.