USGS On the Road - Sampling in the Dark

Are you afraid of the dark?

Not this scientist. He is using a special technique to examine sediment samples that can help scientists study historical hurricanes.

Turns out, the last time this soil saw the light of day was 1972, when it was being pelted with rain. But not just any rain, rain from a hurricane that devasted the east coast and etched its name into the history books (and sediment): Hurricane Agnes.

Physical Scientist Zach Clifton is on the hunt for sediment layers that were deposited during flooding from Hurricane Agnes, which typically contain larger particles. By scouring the sediment core for these layers, Clifton is increasing scientists' understanding about the flooding caused by large hurricanes like Agnes.

To confirm he’s found a layer deposited by Agnes, Clifton used optically stimulated luminescence dating. To use this dating technique, the samples must be kept in the dark. 52 years later, this soil finally saw the light again, but a different kind of light, a red light which doesn’t affect the dating technique.

It works because radiation from the sun causes reactions within the sediment, so the sample can be fated by examining the decay of molecules known to react to sunlight. Since the rate of decay is known, scientists can look at the amount of decay and work backwards to the last exposure of sunlight.