Looking at the picture of the island I would say that this was a case of an eruption with half the side sliding off into the sea. I found a photo of this with the kilometer shown by comparison. The new volcano has a diameter of almost 1/2 kilometer. That means the caldera is 10 to 12 kilometers in diameter or 6 to 8 miles in diameter. Pinatubo left a crater 3 miles in diameter by way of comparison.
https://en.wikipedia.org/wiki/Pico_do_Fogo