NOAA Office of Ocean Exploration and Research, 2017 American Samoa. Download larger version (mp4, 18.9 MB).
What does lava look like after it has cooled underwater? Well, it looks like this.
These pillow lavas were imaged in 2017 at Vailulu'u Seamount, within National Marine Sanctuary of American Samoa. Scientists think the lava flows are likely less than five years old, meaning they are pretty young (geologically speaking). The lava erupted and was instantly cooled by the chilly seawater — creating a snapshot in time.
Learn more about Vailulu'u here.