Why do submarine lava samples offer advantages over samples from land?
Because molten lava chills rapidly underwater, trapping gases and preventing further crystallization, and because the rocks are not exposed to acidic rain and rapid weathering as they are on land, the outer glassy rinds retain the composition of the melt and interior crystals often remain in good condition. From them we can tell eruption temperatures and depth, differentiation due to storage in magma chambers, which volcano produced the flow, what evolutionary stage the volcano was in at the time, and possibly the age of the flow.
