It is sort of like an iceberg in that we only see a small portion of what's there. The island of Hunga Tonga is only a small portion of the rim of the caldera (the summit crater) of a large volcano that is primarily underwater. Here's a view of the seafloor topography & island: pic.twitter.com/1UqAcuYIdF

— Alex Spahn (@spahn711) January 15, 2022