San Francisco Peaks
Composite or stratovolcanoes have sharp peaks or less steep sides. Mount St. Helens, Mount Fuji, and the San Francisco Peaks, seen here in the distance, are examples of this classic volcano type.
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Curtain of Fire
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)
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Survival in Extremes
Notice the different patterns of vegetation around you. Volcanic eruptions alter plant communities, destroying some, creating new habitat for others, and changing growth rates for those remaining. On the lava flow in front of you most soil has come from wind-blown material that collects in cracks and holds water. Consequently, soil and moisture vary dramatically across the flow. And, since seeds blow in, colonization is quite random. Classic succession with lichens breaking down rock into soil, and plants returning in predictable sequence is not occurring here.
As plants return to the barren landscape, so do the animals that use the plants for food and shelter. Many animals that live here are nocturnal. Some take shelter in the lava flow. Others blend in so well with their surroundings that they are difficult to spot. A careful observer may see evidence such as tracks or droppings.
Paricutin
Volcanic eruptions may seem destructive but they are among the beneficial forces of a living planet: forces that build mountains, create oceans, and provide for live. Only when our planet has finished cooling will there be no volcanoes. Then, Earth will be a dead planet much like Mars. The eruption of Parícutin in Mexico, 1943, is considered the modern day equivalent of the Sunset eruption.
Dating Debates
What if scientists always agreed, never argued, or changed their minds?
Clues in Buried Homes: Until archeologists discovered Sinagua-style pithouses beneath the cinders, scientists did not suspect Sunset Crater was so young. Knowing the age of the pithouses from tree-ring dates and pottery types found in these homes, they concluded the eruption occurred after 1046 and before 1071.
Patterns in Tree Rings: Trees near an erupting volcano, if they are injured but continue to live, show a growth disturbance in their rings. Based on the growth pattern seen in three wood specimens from nearby Wupatki Pueblo, scientists hypothesized that the eruption occurred between the growing seasons of 1064 and 1065. But, this evidence is limited and inconclusive.
Magnetism in Rocks: Geologists have taken more than 100 core samples from the Sunset Crater lava flows for paleomagnetic studies. Using both paleomagnetic dating and stratigraphic evidence, geologists currently restrict the Sunset eruption to sometime between 1040 and 1100.
Obsidian Projectile Points
Description: Obsidian projectile points. Dimensions: Left-2.3 cm (L), 1.0 cm (W), 0.3 cm (Th), Middle-2.7 cm (L), 1.3 cm (W), 0.4 cm (Th), Right-1.78 cm (L), 1.22 cm (W), 0.4 cm (Th). Collection: On display at the Sunset Crater Volcano National Monument Visitor Center (catalog card 1, catalog card 2, catalog card 3).
Basalt Cylinder
Description: Cylinder made from scoriaceous basalt. The maker ground the stone to create this shape with rounded ends, but the function is unknown. Dimensions:8.6 cm (L), 2.73 cm (Diam). Collection: On display at Sunset Crater Volcano National Monument Visitor Center (catalog card).
Basalt Mortar
Description: Small circular basalt mortar or bowl. Dimensions: Unknown. Collection: On display at the Sunset Crater Volcano National Monument Visitor Center (catalog card).
Basalt Mano
Description: Rectangular basalt two-handed bifacial mano. Dimensions: 18.5 cm (L), 10.0 cm (W), 3.27 cm (Th). Collection: On display at the Sunset Crater Volcano National Monument Visitor Center (catalog card).
Basalt Mortar
Description: Basalt mortar or grinding bowl. Dimensions: 6.5(Height),13.3 cm(Diam). Collection: On display at the Sunset Crater Volcano National Monument Visitor Center (catalog card).
Basalt Pottery Anvil
Description: Basalt pottery anvil. Dimensions: Unknown. Collection: On display at Sunset Crater Volcano National Monument Visitor Center (catalog card).
Miniature Rio de Flag Brown Bowl
Description: Miniature Rio de Flag Brown bowl with irregular incisions on one side. Dimensions: 1.97 in (Height), 0.2 in (TH), 2.8 in (Diam), 1.46 in (Neck Diam). Collection: On display at the Sunset Crater Volcano National Monument Visitor Center (catalog card).
Miniature Sunset Red Smudged Bowl
Description: Miniature Sunset Red Smudged bowl. Dimensions: 6.1 cm (H), 9.4 cm (Diam). Collection: On display at the Sunset Crater Volcano National Monument Visitor Center (catalog card).