Home / National Park Service Exhibits / Sunset Crater Volcano National Monument (SUCR) / Virtual Trail Guide - Lava Flow Trail 29
- Why are Volcanoes Here?
Most volcanoes are found along tectonic plate boundaries where continents and seafloors collide or move apart. We are far from a plate boundary; consequently, geologists debate why volcanoes occur here. One theory proposes that the North American plate is moving over a stationary “hot spot.” But this theory does not explain why there are young volcanic fields all along the southern margin of the Colorado Plateau and then east to New Mexico and Oklahoma. Another more accepted theory focuses on a disruption in the flow of Earth’s mantle at the boundary between the Colorado Plateau, where the Earth’s crust is very thick, and the Basin and Range region (to the south and west), where the crust is very thin. At this transition, heat from the mantle rises and melting occurs. Ancient faults, activated by stretching of the North American plate (which has created the Basin and range and is extending into the Colorado Plateau), serve as pathways for magma to move to the surface. - 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. - 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. - Taking Root
When the lava flowed and the cinder cone formed, all plant life within a several mile radius was destroyed. The oldest ponderosa pine trees here today are about 400 years old and are probably not the first generation to return. Unlike Hawaii where abundant moisture promotes plant growth soon after eruptions, precipitation here averages only 16 inches (41 cm) a year. Furthermore, soil is sparse in this dry climate where water limits plant life and organic material breaks down slowly. Notice the massive trailing root system of this dead tree. Trees growing on these cinder slopes face extraordinary challenges in finding anchor in loose, unstable cinders and in capturing water as it drains rapidly through them. Notice also how this tree spiraled as it grew. Ponderosa pines grow either straight or dextrally (spiraling to the right). Spiral growth reduces the overall strength of a tree but increases its flexibility. The spiral grain also provides an even distribution of water from a single root to all of the needles and of nutrients from a single branch to all the roots. In a straight tree, wind-damaged branches or damaged roots would deprive water and nutrients to the roots directly below and branches directly above. By spiraling, this tree was better adapted to the stresses of its environment: lack of water, high winds, and occasional heavy snow. But it wasn't able to remain anchored when its roots were exposed by erosion from foot traffic. - Miniature Volcanoes
On the slope below you is a small spatter cone. Spatter cones, or hornitos (“little ovens” in Spanish), form when lava is forced up through an opening in the cooled surface of a lava flow. They are “rootless,” fed by the underlying flow rather than a deep magma conduit. Can you picture fluid fragments of liquid spurting upward, flattening, congealing, and mounding around the opening? Can you imagine approaching an erupting spatter cone? Unique artifacts found nearby – corn casts in lava rock – suggest people did. Experiments conducted in Hawaii demonstrated that “corn rocks,” like the one on display in the visitor center, can form when ears of corn are covered by fluid blobs of spatter. It appears people intentionally ventured close to an active hornito, maybe this one, to leave corn – perhaps as an offering. More than 50 rocks with corn casts have been found in homesites attributed to the local Sinagua cultural tradition. - Hornito
- Undercurrents
Beneath the lava you now stand on are perhaps dozens of caves. As lava flowed, the top surface cooled first due to contact with air. A hardened crust formed. Meanwhile, rivers of lava continued flowing below, periodically breaking through the crust to form the spatter cones you saw earlier. When the flows ceased, the remaining lava drained out the downhill end of the crusted-over channels, leaving behind tube-like caves. Most of these caves were sealed with hardened lava and have no openings to the surface. A collapse created the opening you see here. - 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. - 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. - Penstemon
Along the perimeter of the flow, a unique microhabitat for plants exists. In places, water collects on the surface of the flow and is then channeled through fractures to the edge where it locally benefits plants. White-barked aspen trees grow around the perimeter of the flow and along fracture systems. In area of deep cinder, like the dunes in the distance to your left, specialized plants have evolved. The Sunset Crater penstemon evolved new traits which allow it to live on cinder soils but also make this endemic plant dependent on this habitat. It cannot survive elsewhere. - Changes to Come
- Give and Take
From the earliest times, people have enjoyed the long-term benefits of volcanic eruptions. People journeyed long distances to volcanic areas to gather materials for their daily lives, including important minerals, raw materials like obsidian for tools, and building supplies. And always, in return for these benefits, people have paid a high short-term price in the form of volcanic disasters. Our culture influences how we forecast events, choose to prepare and adapt to catastrophes, and how we explain our world and its phenomena. Some of us look to science, some to religion, and some to traditional knowledge. It is not surprising that worldwide, when people live near volcanoes, they often develop related rituals and belief systems. This eruption was a significant event in the lives of the native peoples of the Southwest, and today all of the region’s American Indian groups consider this a scared landscape. - Power to Symbolize
- Traditions
The ancestors of today’s Hopi and Zuni Indians witnessed the eruption. In some Hopi accounts, the Qa’na Katsina caused Palatsmo (Sunset Crater) to erupt after people engaged koyaanisqatsi, a life out of balance. For Hopi people, Palatsmo is a living reminder: if people stray from their religious ideals and lifeway, there may be another eruption. In Zuni traditions, stories of the eruption were carefully guarded because of the belief if people continually dwell upon negative events those events will happen.
Regardless of our worldview, places like Sunset Crater Volcano National Monument help us to better understand each other and the forces that continually affect our lives.