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Current, which sweeps up the western coast of South America, carrying cold water from Antarctica. At the Equator, it turns west past the Galápagos Islands and out into the Pacific Ocean. The cold waters of the Humboldt Current are rich in micro- scopic food, which supports much of the wildlife in the region. But each December, the current gets weaker as the strong winds that drive it ease off. This allows warmer water, very poor in food, to flow in from the north. This seasonal effect is called El Niño. It usually lasts for four to six weeks, but every few years, it can last for up to nine months, wiping out the food supply in the region. Fish vanish, seabirds starve, and the warm water disrupts the climate, causing droughts and coastal flooding throughout the tropics. The opposite of a strong El Niño year is known as La Niña. During a La Niña period, the Pacific Ocean has cooler-than- usual temperatures at the Equator. A La Niña period often, but not always, follows a strong El Niño period. In the United States, the impacts of El Niño and La Niña can be most clearly seen during wintertime. During El Niño years, winter temperatures are warmer than normal in the Midwestern states, and cooler than normal in the Southern states. During a La Niña year, winter temperatures are gener- ally warmer than normal in the Southeast and cooler than nor- mal in the Northwest. Waves and Tides The wind also heaps up the waves that roll across the oceans. Waves are ripples on the ocean surface, like the ripples on the surface of a pond. Yet the weight of water in a wave can be

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Oceans