If you lived your life like a volcanic island, you would spend a long time growing without anyone knowing you were there, have an explosive debut into the atmosphere, continue growing but become much less explosive resulting in a bunch of resort hotels being built all over you, become so heavy you make the ground sink underneath you until you disappear from view and then end your life by falling in a ditch.
All volcanic islands spend part of their lives as seamounts, but not every seamount follows this life plan. Some seamounts never rise above the surface. Some, like the Louisville Seamount Trail, became islands at the wrong time in Earth’s history to be vacation destinations for human beings. Also, since we have explored less than 1% of the world’s estimated millions of seamounts, there is a good chance there is a lot more variety amongst them than what has been observed so far. Except for the resort hotel thing, this does appear to be the life story of the seamounts we are drilling on.
A seamount’s life begins when lava begins to erupt out of the ocean floor. In the deeper ocean, when the hot lava comes in contact with the cold ocean water, the outmost edges of the lava immediately solidify into a bulbous shell, resulting in a type of rock known as pillow basalts (see the NOAA photo below).
If the eruptions continue, they keep building up layers of basalt, one on top of the other until it reaches the surface. Once it reaches shallow water, the combination of lava, water and low pressure becomes literally explosive, causing lava to splatter and cool in small, angular chunks (see the USGS photo below) that eventually settle together and are cemented by limestones forming breccias, a type of rock that our geologists are very familiar with.
Once the seamount has risen high enough that the lava is no longer in contact with the water (i.e. it has become an island), the lava flows out gently and forms the kind of volcano found on the Big Island of Hawaii. Seafaring birds that ate fruits and berries on other islands begin finding the new island and poop all over it, leaving seeds and fertilizer that allow plants to grow. Thanks to bird poop, the island eventually resembles a tropical paradise on a travel brochure.
To learn about the death of a volcanic, read my next blog.