Bread Crust Bomb: 1912 Novarupta eruption

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In Katmai National Park, a massive ignimbrite deposit was left in the Valley of Ten Thousand Smokes after the 1912 Novarupta/Katmai eruption. Following the main eruption, two lava domes emerged at the Novarupta vent. A small explosion destroyed the first dome, sending bombs crashing over the surrounding ignimbrite. One of these bombs measures approximately 1.5 meters wide and lies about 100 meters from the present-day Novarupta dome. This bomb was formed when hot lava burst forth as the dome collapsed. Gases within the magma continued to escape into bubbles (vesicles), causing the bomb to swell dramatically. As the inside of the bomb expanded, its surface cracked and developed a bread crust texture. Large bubbles are visible inside the bomb, while smaller ones line its outer surface, which cooled faster than the interior.