A glacier in Patagonia, Argentina, calves, with a sudden collapse of ice. Researchers say that the activity that precedes these types of tipping points and the triggers that cause them may follow predictable patterns.
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Supporters of ousted and deposed Honduran President Manuel Zelaya march during Independence Day in Tegucigalpa, Honduras, on Tuesday. Zelaya has vowed to return to the country and reclaim his office.
Orlando Sierra/AFP/Getty Images