Like a glassblower who blows air into molten glass to create a goblet or vase, gas released from lava may force the thin, glassy crust of a lava ﬂow to form a large circular bubble or blister. Blisters may also form through hydrostatic or artesian forces in the lava. They are usually one hundred to ﬁve hundred feet in diameter, with a maximum height of one hundred feet, and are hollow. The largest may form blister caves, although the geologic situations where this happens are rare, the most common being a calm volcanic eruption. Generally, blisters are too small to enter, but the more tenacious the lava is, the bigger the bubbles can become. The largest blister caves are found at Mount Fantale, Ethiopia. The basaltic lava ﬂows of the Kilauea Volcano in Hawai‘i have created smaller but no less deﬁned lava blisters.