Because gigantic volcanic eruptions involving pacific islands were completely unknown in the nineteenth century? https://en.wikipedia.org/wiki/1815_eruption_of_

Because gigantic volcanic eruptions involving pacific islands were completely unknown in the nineteenth century? https://en.wikipedia.org/wiki/1815_eruption_of_Mount_Tambora https://en.wikipedia.org/wiki/1815_eruption_of_Mount_Tambora