The volcanic activity they talk about at the end of the Cretaceous are not single volcanos like St Helens, Krakatoa,
or even Yellowstone size eruptions. They are talking about the outpouring of the Deccan Traps in Western India. These flood basalts covered 193000 square miles to a depth of 5660 feet or about 123000 cubic miles of basalt lava. The largest outpouring lasted about 30,000 years. The same is true at the end of the Permian. The Siberia Traps eruptions lasted less than 1 million years but poured 720000 cubic miles of lava onto Northern Siberia.
Excellent point. One theory I had was that the Yucatan meteor shocked the Deccan area so severely that it cracked and oozed for thousands of years. Then I read about the theory by an Indian scientist that there was a huge strike off the coast of Mumbai. I think he called it the Shiva Crater and his name may be Sattargee or something like that.
I know that there are at least strikes associated with the Chesapeake Meteor about 34MYA, there is also the Toms River crater and Popogai in Russia.