Bread Crust Bomb: 1912 Novarupta eruption

In Katmai National Park, the 1912 Novarupta/Katmai eruption left a huge ignimbrite deposit in the Valley of Ten Thousand Smokes, but after the main eruption, two lava domes formed at the Novarupta vent. The first dome was destroyed by a small explosion that spread bombs over the ignimbrite around the vent. This bomb is approximately 1.5 m wide and located about 100 m from the present Novarupta dome. The bomb formed from hot lava extruded when the dome collapsed. Hot gasses in the magma continued to exsolve into bubbles (vesicles), which caused the bomb to expand. The expantion of the inside of the bomb caused the surface to fracture and form the bread crust texture. Large bubbles are found inside the bomb, but small bubbles are on the outer surface, which cooled faster than the inside.