The Wakashio, a large cargo ship chartered by Mitsui O.S.K. Lines, ran aground off the coast of Mauritius, an island nation in the Indian Ocean: some 900 km east of Madagascar. The accident spilled a huge amount of the ship's fuel, causing extensive damage to coral reefs and wetlands. People are now asking about the vessel's itinerary, how the accident occurred and the extent of the damage. Aerial photos and tracking data can answer some of these questions.

The Wakashio ran aground in waters 1.4 km southeast of Mauritius. Mauritius is located along busy sea lanes that see more than 2,000 vessels pass by each month. The waters around Mauritius are shallow. The ship's original route was to take it more than 32 km from the island.

It is believed that the vessel deviated to the north due to heavy seas. There are also reports that Mauritius' National Coast Guard had issued a warning that the ship was too close to shore, but that it approached land so that crew members could use their mobile phones.

Local police are gathering information on the ship's communications from recording devices that will provide more details on the accident. Nagashiki Shipping, the company based in Japan's western Okayama Prefecture that hired the crew, and Mitsui O.S.K. Lines, which chartered the ship, have not been able to speak with crew members as the captain has been arrested by authorities in Mauritius.

The Wakashio is a 300 meter-long bulk carrier. Bulk carriers are designed to transport natural resources and foodstuffs -- mainly iron ore, coal and grain -- in the open air. The Wakashio has five fuel tanks at the stern, four on the starboard side and one on the port side, which contained a total of about 4,000 tons of fuel when the vessel ran aground.

When full, cargo is carried amidships, but the ship's hold was empty when it ran aground. The Wakashio was sailing to Brazil to prepare for a possible request to transport iron ore.

According to Mitsui O.S.K. Lines, the ship's operator, and Nagashiki Shipping, the owner, the engine room began flooding after the ship ran aground on July 25. The two companies asked a salvage company to remove the fuel, but winter weather and high waves made operations difficult. The vessel was pushed by the current in a northeasterly direction from where it ran aground, damaging the hull, they said.

The vessel was confirmed to be leaking fuel on Aug. 6. Of the ship's five fuel tanks, the foremost tank on the starboard side, which contained 1,180 tons of heavy oil, was ruptured, spilling fuel into the sea. The Wakashio's hull broke in two on Aug. 15. No equipment failures or malfunctions have been confirmed on the ship so far.

Structure diagram of Wakashio

Mauritius' coral reefs are thought to contain 40% of Earth's hard coral species. This raises the question of how much environmental damage there will be to this rare and fragile ecosystem. If heavy oil adheres to corals, they suffocate and die, experts say. It can take decades for an area contaminated with oil to recover.

In addition, the spill is spreading to wetlands and mangrove forests about 2.8 km west of the grounding site. The area is registered under the Ramsar Convention, which aims to preserve ecosystems that are important to waterfowl and other animals. The roots of mangroves twist and turn in the seawater. They are thick and tangled, making cleaning up oil that washes ashore slow and arduous. There are also concerns about the economic impact of the spill, as one of Mauritius' main selling points to tourists is its pristine environment.

In 2010, an accident at an offshore oil platform in the Gulf of Mexico spilled 4.9 million barrels (more than 660,000 tons) of crude oil into the surrounding waters. The Wakashio is thought to have leaked about 1,180 tons of heavy fuel oil so far.

That is a small amount compared with the accident in the Gulf of Mexico. But in 2010 a Chinese ship spilled fuel oil on Australia's Great Barrier Reef and the company that owned the ship was forced to pay the Australian government 3 billion yen ($28.4 million at the current exchange rate) in compensation. The environmental impact of such accidents cannot be measured solely in terms of the amount of oil spilled.

Specialist contractors and volunteers brought in by Nagashiki Shipping and the Mauritius government are collecting the spilled oil with pumps and adsorption sheets. Authorities have not approved the use of chemicals that break down oil, so they cannot be used. There is a shortage of adsorption sheets, according to the Japan Disaster Relief Expert Team that was dispatched to the site by the Japanese government.