Centuries of Hurricane Records Deciphered

An Alabama lake has dutifully recorded when catastrophic hurricanes have pounded the coast during the last 700 years. Now scientists have unravelled the lake's history of severe storms by deciphering a core sample they've taken from the lake's bottom. The core reveals that major hurricanes have sometimes come in clusters.

The most powerful hurricanes left their signatures when they dumped seawater into Lake Shelby. The normally freshwater lake sits about 250 metres (820 feet) inland from the Gulf of Mexico, separated from the ocean by sand dunes. A storm surge produced by Hurricane Ivan in 2004 flooded Lake Shelby with Gulf waters, as have other severe hurricanes in the past.

The boost of nutrients from the ocean eventually leaves its mark in the muck at the bottom of the lake. With the extra nutrients, Lake Shelby grows more algae. The temporary spike in organic production gets recorded in isotopes of carbon and nitrogen left in a layer of sediment.

A sediment core that researchers extracted from the lake's center showed 11 nutrient spikes occurring between 1320 and 2002 when the lake was flooded with a storm surge. One of the spikes corresponds to a devastating unnamed hurricane that hit in 1717. A French ship carpenter living in Mobile at the time, André Pénicaut, recorded in his journal that the storm completely destroyed the port city while people and animals drowned in the storm-waves.

The 11 hurricanes that have pushed ocean waves into the lake did not arrive at regular intervals. Five of the storms happened in 60 years, from 1460 to 1520. They were followed by 180 years without storm surges. The core shows another two catastrophic hurricanes hitting during the 1800s and one in the mid-1900s.