Answer:
The type of volcanic material that indicates an eruption under water is pillow lavas. Pillow lavas are formed when lava erupts under water or flows into water, causing it to cool rapidly and solidify into pillow-like structures. These structures are typically smooth on the outside and have a fine-grained texture on the inside, and are often found in submarine volcanic environments such as mid-ocean ridges and submarine volcanoes. The other types of volcanic material mentioned, aa flows and pahoehoe flows, are formed by lava flowing on land and are not typically associated with underwater eruptions.