On the morning of December 26, 2004, a massive earthquake shook the seabed off the coast of Indonesia. It was so powerful that it shoved part of the seafloor upward and sent a wall of water rushing across the Indian Ocean. By the end of the day, the tsunami had reached 14 countries, becoming the deadliest in modern history.
Out in the open sea, the wave was only a few feet tall - ships barely felt it pass under them. But as it raced toward the coast at over 500 mph, it slowed down and piled up. By the time it hit shorelines in Indonesia, Sri Lanka, India, Thailand and Africa, the water rose into walls over 100 feet high.
After the disaster, countries around the Indian Ocean built a network of sensors floating on buoys to detect new tsunamis. If a wave forms, the buoys radio satellites, which send alerts to phones and TVs in seconds. The system has already saved many lives - turning a tragedy into the start of a much safer warning network.
