Olympus sized vulcano found under the pacific.

[Anomalocaris]

What happens when an Olympus-sized underwater volcano erupts? eeek!

Some future generation gets more oil.

Seriously, surprisingly little happens to the life on earth. No mass extinction event has been found that could be correlated to tamu massif eruption. Nor indeed has one been found to match the even larger Ontong java underwater eruption which occurred 20 million years later then the tamu eruption. Appearently the impact of these giant underwater volcanic eruption on the biosphere seems minor considering the enormous size of these eruptions. This is in contrast to similar sized eruptions on land, which has been correlated with some of the largest extinction events in history.

But the later Ontong java eruption is closely correlated with a profound change in deeper ocean chemistry, resulting in a sharp spike in the formation of patroleum bearing shale rock strata on sea floors world wide. Tamu eruption has also been proposed to have caused a minor surge in formation of oil bearing shale. So these volcanos may be directly responsible for a good portion of the world's patroleum deposits.