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Meanwhile, lava broke out of the base of this side of the cinder cone forming the Bonito Flow all around you. The lava pooled, trapped by surrounding older volcanoes, and accumulated to perhaps 100 feet (30 m) thick during at least three separate flows. On the opposite of the cone, lava flowed more than six miles (10 km), filling a narrow valley.

When the volcano coughed out its last cinders – after several months or perhaps several years – they were colored by the oxidation of iron in the magma. Similar to the way metal rusts, the magma came in contact with water-rich gasses emitted during the final stages of the eruption. These red cinders rim the top of the cone.



  • Eruption date: sometime between 1040 and 1100
  • Height: 1,000 feet (305 m)
  • Elevation at summit: 8,029 feet (2,447 m)
  • Diameter at base: 1 mile (1.6 km)
  • Diameter at top: 2,250 feet (868 m) from rim to rim
  • Depth of crater: 300 feet (91.4 m)
  • Extruded material: approximately 1 billion tons
  • Extent of ashfall: approximately 800 square miles (2,072 sq km)