Blowhole (geology)

Mechanics

Blowholes form in coastal rock where crevices like lava tubes exist, especially along fault lines and on islands. When strong waves hit the shore, water forces its way into these openings and shoots out under high pressure, often with a loud boom and a wide spray, which makes them popular with tourists. These features are created by marine erosion on rocky coastlines and can be found worldwide, particularly where faults intersect and on windward shores that face the open ocean’s higher wave energy. A blowhole develops alongside a littoral cave, and together they form a blowhole system. Every such system has three parts: a catchment entrance, a compression cavern, and an expelling port. The arrangement, angle, and size of these parts control the force of the air-to-water mixture that blasts out. The blowhole itself sits at the far end of the littoral cave. As the name suggests, blowholes can move air quickly; strong reverse drafts from pressure shifts in the connecting cave can push wind speeds over 70 km/h. The system starts when a littoral cave forms, driven by wave action and the rock’s properties. How easily the rock weathers—whether it resists or breaks down—greatly affects cave development. Littoral caves form in two ways: limestone caves come from karst (dissolution) processes, while igneous rock caves come from pseudokarst (non-dissolutional) processes. Over time, the cave grows inland and upward along weak joints in the rock. As weathering wears on, the cave roof gets exposed and the blowhole widens; eventually the roof weakens and collapses, leaving a steep-walled inlet that leads to the next stage of coastal change. A large example is La Bufadora on the Punta Banda Peninsula in Baja California, Mexico. It is a littoral cave with a narrow opening that erupts every 13 to 17 seconds, shooting water up to 100 feet above sea level.