"This island is home to caves of great snotty stalactites, secretly named after Snotlout for their undeniable "charm"."
―Dragons: Rise of Berk
According to the Official Description, Snottite Stop is riddled with large caves containing stalactites (and therefore stalagmites). Though it is unclear what exactly a "snotty" stalactite is, it might be presumed that the stalactites are actively forming and are therefore wet and drippy with mineral-laden ground water. Their presence also implies a very wet island and one rich in limestone. There are volcanic stalactites, however, the adjective "snotty" would make less sense.