Waves quickly exploit joints, cracks and bedding planes in rock through hydraulic action. (Pressure is created when waves force air into crevices, pressure is released as waves retreat creating mini explosions.) Along the joint the sea will cut inland to form a cave. If the erosion continues upwards then with a little help from sub-aerial processes the line of erosion continues through the cliff to the top forming a blowhole. Blowholes get their name due to sea spray coming up and out in stormy weather much like a dolphin or whales blowhole.