Why blowholes?

Several people have looked puzzled when I talk about blowholes in the desert because they have seen coastal blowholes spraying water into the air.

These blowholes are a long way from the coast and they blow air.

Early explorers saw and heard the air rushing in and out of the caves. Many of them were familiar with the sea breeze that blows on shore and assumed that the coastal winds were pressurising the underground caverns.

There are two major influences on the strong drafts that blow in and out of the underground caverns.

The first driving force is the temperature. During the day when the outside air may reach 40 degrees Celsius and the air in the caves is cold the air blows out to equalise the pressure. (Hot air is not as dense as cold air.)

At night the situation is reversed. The outside air can fall below freezing on a frosty night while the caves maintain about 10 degrees Celsius. The caves draw in the colder air.

The other influence is the barometric pressure changes of the weather cells. A large high pressure cell may stand over the caves for days forcing air into the cave system. When it is displaced by a low pressure cell the air is released from the caves.