Conveniently, sand grains washed onshore during storms (see photo above) have a special way of tracking the time since the moment they came to rest. Deciphering this code made it possible for researchers from Delft University of Technology in the Netherlands to identify the timing and extent of a record-breaking storm that hammered the Dutch coastline in the 1770s.
In this case, the scientists were able to match the dune record to historical reports, which provide nifty verification that their sand grain analysis holds water. But the really cool implication of their work is that systematic scouring of coastal dunes anywhere in the world could turn up records of coastal flooding no one was there to see. That’s why the team, led by Jakob Wallinga, earned the cover story in the upcoming November issue of the of the journal Geology.
The more scientists know about past events, the better they can predict the future. Knowledge of specific storms is vital for strengthening statistical predictions about how often storms occur and how storm tracks change over time. Those changes are particularly important because many weather patterns, such as the weird ones that plagued Europe and North America this past spring, are a result of multiple forces.
Low-lying countries such as the Netherlands are especially keen to get a handle on the changing threat of floods from the seas. Fewer people may be dying in extreme weather events now than in the past, but many more severe events are being reported.
And severe weather, particularly along the world’s heavily populated coastlines, is bound to get worse as global climate warms.
A major stumbling block in making good predictions is that no one kept rigorous records of storm surges and related flooding until the late 1800s. That’s where the sand grains come in; they can give scientists a record of all sorts of past storms not yet accounted for. Here’s a quick analogy for how the method, called optically stimulated luminescence, works:
Think of each sand grain as a rechargeable battery. Exposure to sunlight (say, as the grain churns in the roiling surf) zaps the grain’s charge to zero. But once the grain is buried (as the storm abates), it accumulates a charge at a predictable rate from the minuscule dose of radiation that surrounds us all the time (because radioactive elements in the Earth’s crust emit radiation as they decay). So, if scientists can extract the grain from its burial place without exposing it to light, they can shine their own lights on it in the lab to capture a signal that lets them calculate the date the grain’s charge was last reset.
Wallinga’s team extracted their prescient sand grains story from dunes piled up near the town of Heemskerk. The initial clue turned up in a fresh cliff face chiseled into the seaward side of the dunes during storms in 2007. Sandwiched among the newly visible sand layers was a convoluted bed of intact shells and chunks of brick too heavy to have blown in on the wind; only the pounding surf of a storm surge could have carried the debris that far, in some cases ripping the live animals from their seafloor homes before sweeping them landward.
By mapping this debris layer using ground-penetrating radar, Wallinga’s team determined from the sediment that at some point floodwaters had reached far higher than any other storm surge on record in the Netherlands, including one that killed 2,000 people in 1953. Luminescence dating of sand grains nestled among the shells pegged the storm as happening sometime between 1760 and 1785 -- which matched perfectly with written accounts of major storms that occurred in 1775 and 1776.
Read more at Discovery News
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