The Great Blue Hole is a giant, nearly perfect circularmarine sinkhole located off the coast of Belize. Measuring over 1,043 feet across and 407 feet deep, this site was not always underwater; it originally formed as a massive limestone cave system on dry land, when sea levels were much lower. As the oceans rose, the cave flooded and its roof collapsed, creating the deep blue circle we see today. The hole was made famous by explorer Jacques Cousteau and remains a top diving destination where visitors can explore massive underwater stalactites and stalagmites that prove its ancient, dry-land past.
Project
Draw a picture of you and your family on a boat over the Great Blue Hole.
Overview
Dimensions
By U.S. Geological Survey (USGS) – Source: [1], fetched September 2006. Caption on this USGS web page was, “Blue Hole: Aerial view of the 400-ft-deep oceanic blue hole (Lighthouse Reef Atoll Blue Hole) located east of Belize.”, Public Domain, Link
It formed over 150,000 years ago as a giant dry cave on land during the Ice Age when sea levels were much lower.
Deep inside the hole, divers can see huge stalactites (like icy drips hanging from a cave ceiling). These stone formations could only have formed when the cave was filled with air, proving it was once dry land.
It is famous for being almost perfectly circular! It is the largest natural feature of its kind in the world.
The hole is so large and its color is so dark compared to the surrounding shallow reef that it is easily seen from space!
If you dive deep enough (around 300 feet), the water becomes toxic and has no oxygen. This means the bottom of the hole is dark and almost completely without life.
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December 1, 2025
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