During the search for Malaysian Airlines Flight 370, experts have found lost shipwrecks and undiscovered volcanoes.

But they have not found any wreckage from the missing jetliner.

The passenger plane was traveling from Malaysia to Beijing, China, in March 2014. The flight disappeared over the Indian Ocean. On board were 239 people, and all are presumed dead.

An American company specializing in underwater searches will examine the waters off the west coast of Australia. The company will scan large areas of the ocean floor. A Chinese rescue ship will assist looking for MH370.

The Malaysian aircraft is thought to have crashed in very deep water. Parts of the Indian Ocean in the area are up to 6,000 meters deep. Searches have failed to find any debris.

An undated handout sonar image released by Joint Agency Coordination Centre (JACC) on Jan. 13, 2016 shows an iron or steel-hulled shipwreck some 3,700 meters below the surface and believed to have gone down at the turn of the 19th century.

The ocean floor in the search area is treacherous. An Australian search report mentioned "underwater mountains, crevasses, ridges and 2,000-meter sheer cliffs," are making missions difficult.

An underwater sonic device collided with a tall mud volcano in January. The cable snapped, and the device sunk to the ocean floor.

But two shipwrecks have been found. Sonar photos found a ship made of steel or iron from the 19th century. Wreckage from another ship was located in May.

The only wreckage of Flight 370 found so far was a piece of the plane washed up on Reunion Island in 2015. Reunion Island is in the western Indian Ocean near Madagascar.

The search area is now limited to 60,000 square kilometers off of Australia. Investigators say they will end all search efforts in June.

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Words in This Story

jetliner – n. a large jet airplane used for carrying passengers

treacherous – adj. very dangerous and difficult to deal with

debris – n. the pieces that are left after something has been destroyed

crevasses – n. deep, narrow openings or cracks in an area of thick ice or rock

cable – n. a thick, strong rope made of wires that are twisted together

sonar – n. a device used for finding things that are underwater by using sound waves