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- BuriedHomes
- One Volcano Amid Many
At nearly 1,000 years young, Sunset Crater volcano is a geological infant, the latest development in a series of eruptions that have taken place here over the past 6 million years. It is only a small part of the impressive San Francisco Volcanic field of northern Arizona. From this point, three different types of volcanoes are visible. What makes a volcano tall or short, steep or gentle, or an eruption more or less violent? Mostly the magma’s stickiness or viscosity, which is determined by its chemical composition and gas content. Cinder cones, like Sunset crater and most of the 6000 or so volcanoes in this field, tend to be cone shaped with sides not steeper than 33 degrees. A cinder cone is literally a pile of loose fragments. It is easily eroded and will change shape, becoming less steep as it ages. - O'Leary Peak
Look for a dome volcano (O’Leary Peak) on the horizon in front of you. Dome volcanoes tend to have steep sides and rounded shape. - An Explosive Past?
On the horizon, the San Francisco Peaks rise as the highest mountains, forming the dominant feature of the san Francisco Volcanic Field. Imagine the sides continuing up to form one 16,000-foot-high mountain. This may be what the stratovolcano looked like about 500,000 years ago. The summit and flank of the volcano may have exploded and collapsed, much like Mount St. Helens. Erosion over thousands of years has created several peaks from the original volcano. Humphreys Peak, standing at 12,633 feet, is the tallest and is the highest peak in Arizona. How did they get their name? The peaks were named in 1629 by a group of Franciscan missionaries in honor of St. Francis of Assisi. In 1847, a small West Coast settlement on the verge of becoming a boom-town changed its name from Yerba Buena to San Francisco. This happened more than 300 years after the Arizona peaks were christened. - Hornito
- Surface Currents
Looking beyond the lava and spatter in front of you, and just beyond the line of trees, can you see a reddish hill? This is an agglutinate mound or pile of welded pyroclastic material. In the early stages of the eruption, a cone began to form next to a major explosive vent. The cone became armored by welded deposits. Then a column of dense magma broke through the base of the cone, causing the upper part of the cone to collapse onto the top of the flow. The slumped pieces were then rafted away by the flowing lava. You are looking at a large piece of an early-stage cone of Sunset Crater. Perhaps within weeks or days after breaching, the cone was rebuilt, creating the symmetrical cone of Sunset Crater we see today. Any remnants of the earlier cone lie buried beneath tons of cinder. - Xenolith
Patterns often reveal forces otherwise invisible to us. As you cross the bridge, look to your right for a small light-colored rock embedded in the dark basalt rock. This is a xenolith (zee-no-lith), a rock fragment foreign to the body of rock in which it occurs. When magma rose to the surface, it brought up pieces of limestone from 700 to 1,000 feet below us. Uplift and erosion have exposed this rock (known as Kaibab limestone) elsewhere: at the rims of Grand Canyon and nearby Walnut Canyon and in cliffs at Wupatki National Monument. - Kachina Doll
Description: Kana'a Kachina doll carved and painted by Lloyd Masayumptewa. Signed on the bottom with Piiyayouma Masayumptewa "05." Collection: On display at Sunset Crater Volcano National Monument. - Our Dynamic Earth
Alpine slopes, forests, and grassy parks disguise the fiery, molten, and often explosive history of this region’s landscape. But here, amidst the Bonito Lava Flow and Sunset Crater’s cinder fields, the land’s volcanic origin is revealed in stunning clarity. As you walk the trail, use this guide to explore the powerful forces – rapid and violent, slow and patient – that continually shape our planet. These forces all affect our lives and provide for life in ways we may not realize. - A Complicated History
Sunset Crater rises before you, a nearly symmetrical cone. Its perfect shape suggests a simple eruption history, but that was not the case. In fact, it wasn't until the 1980s that scientists began to understand the complexity and extent of the eruption. First, molten rock (magma) and gasses pushed up to the earth’s surface along a six-mile-long weak spot or fissure in the earth’s crust. Volcanic fragments, called pyroclasts, shot upward along the fissure in a “curtain of fire” as gasses escaped violently. Small cinder cones formed along this fissure before the magma became focuses and erupted as a lava fountain from a primary vent. A large cone (Sunset Crater) grew as the shower of cinders and ash piled up around the vent. - Ropes and Clinkers
You are now on the southern edge of the Bonito Lava Flow. Magma, periodically relieved of gas pressure, squeezed out of the base of the cone as glowing liquid lava, creating a structurally complex flow covering 2 sq miles (5 sq km). Lava flows tend to form either jagged blocks, known as aa (ah-ah), or a smooth, ropey surface of pahoehoe (pa-hoy-hoy). Flows usually start as pahoehoe, thin and runny. As the lava cools and becomes more thick and pasty, it can change into an aa flow. The Bonito Flow is mostly aa lava. When aa is forming, cooled, hardened blocks - sometimes called clinkers - are rafted along the surface of moving lava, making clinking noises as they tumble into each other. Although its structure is complicated, the flow’s composition is uniform throughout. The lava and cinders around you, whether black or red, ropey or jagged, are basalt.