The Great Blue Hole of Belize is a round sinkhole in the middle of a shallow lagoon, and have been found on its floor and its walls. Stalactites can grow only in a dry cave with water dripping through it. So what happened there?
It was a dry cave before the sea arrived. The Great Blue Hole is a , a cavity formed where water dissolved limestone. The stalactites on its floor and walls can only grow while a cave is open to the air with water dripping in it, so they prove the cavity was once dry. As the glaciers melted , flooded the cave and left a dark circle some 125 meters deep inside a shallow, bright lagoon.
A dark circle in the middle of a shallow, bright sea looks like a hole in the floor, and it is a sinkhole cut into limestone.
Slightly acidic rainwater dissolves limestone and creates caves, and when the roof of a cave loses its support it collapses inward, which is where the round shape comes from.
The evidence that the place was dry is the stalactites. A stalactite builds as a drop hangs in air and deposits mineral, and under water that process does not exist at all.
As the glaciers melted the sea rose by tens of meters and flooded the cave, which is why stalactites formed in air now lie deep. Those at mark the stages on the way. The sinkhole is a geological sign of a changed coastline this way. Other marine sinkholes formed along different routes, so this is not an explanation for every blue hole.
wat. The underwater stalactites in the Blue Hole of Belize grew in a dry cave before the sea rose and flooded it.
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The sinkhole is a clear geological sign that the coastline and the level of the sea have changed on an enormous scale.
How do we know?
Sediment cores, and mapping of the walls and the stalactites at different depths, reconstruct the stages of the cave and its flooding as the sea rose.
What is still unknown
Other marine sinkholes formed along different routes, so the history of Belize is not an explanation for every blue hole.
Learn something?
Where to next
Was the land under the North Sea a route or a home?sea level
Is sea level rising by the same amount everywhere?sea level