Katrina. Harvey. Maria. Dorian. In recent years, hurricanes have killed thousands of people and caused billions of dollars in damage. But getting a handle on how frequently these destructive storms have pummeled the planet is tough because records stretch back only about a century and a half.

Now, researchers have assembled a 1,500-year history of hurricanes in the Bahamas, based on sand and shell fragments pulled up from submarine caverns known as blue holes. Their results, published in October in Paleoceanography and Paleoclimatology, show that hurricane activity has varied over time. In fact, recent hurricane activity in the Bahamas has been low compared with historical highs, despite intense activity elsewhere in the Atlantic arena. The fluctuations are likely driven by changes in atmospheric and oceanic circulation and volcanism, the scientists suggest.

In the aftermath of Hurricane Dorian and the destruction it caused in parts of the Bahamas, this historical record is “a wake-up call,” said Lisa Kennedy, a geographer at Virginia Tech who was not involved in the research. “We are only beginning to understand hurricane patterns and processes in the context of long-term history.”

Blue holes form when carbonate rock erodes, collapses and fills with water; they are revered among divers for their deep, clear waters. They are also important keepers of the scientific record, as hurricanes wash coarse material like sand, gravel, shells and pieces of coral into them.