火山栓，海底火山爆发时，由于火山顶部是海水，喷涌而出的熔岩一旦接触到海水，便会凝固，形成固体外壳，堵住火山口，然而有时并不能完全堵住，随着岩浆的不断溢出，常在火山口形成一个突起，而后海陆变迁，地面上的火山栓往往成为旅游圣地。著名的火山栓有加州莫洛岩石，斯里兰卡的锡吉里耶。

A volcanic plug, also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of pressure if rising volatile-charged magma is trapped beneath it, and this can sometimes lead to an explosive eruption. Glacial erosion can lead to exposure of the plug on one side, while a long slope of material remains on the opposite side. Such landforms are called crag and tail. If a plug is preserved, erosion may remove the surrounding rock while the erosion-resistant plug remains, producing a distinctive upstanding landform.