Tongue of the Ocean, Bahamas Winter/Spring 1997. The shallow Bahama shelf and the southern portion of the deep Tongue of the Ocean (darker water, upper right) can be seen in this northwest-looking view. The Tongue of the Ocean is one of two main branches that form the Great Bahama Canyon. The vertical rock walls of this submarine canyon rise 14060 feet (4285 meters) from the canyon floor to the surrounding seabed. The Grand Bahama Canyon has been traced for more than 140 miles (225 km) in length. The canyon has a width of 23 miles (37 km) at its deepest point and an average floor slope of about 300 feet per mile (60 meters per km). During the last Ice Age, nearly 12000 years ago, much of the Bahama Shelf was above sea level. Rainfall during that period formed erosional type gullies or small canyons as rainwater flowed off the shelf into the Tongue of the Ocean. As the climate warmed and the ice melted, sea levels rose to present levels covering the eroded gullies seen on this image.