Home / National Park Service Exhibits / Sunset Crater Volcano National Monument (SUCR) / Virtual Trail Guide - Lava Flow Trail 29
The virtual trail guide mimics the paper trail guide and benchmarks you would experience in person when walking the Lava Flow Trail. The text derives directly from the Lava Flow Trail Guide currently used by the National Park Service at Sunset Crater Volcano National Monument, and from interpretive stations positioned along the trail itself.
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.
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.
As Powerful as a Volcano
Changes to Come
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)
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.
Frozen in Time
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.
Hornito
Introduction to the Trail
A sculpture garden of extraordinary shapes and forms awaits you on this walk through the lava flow and cinder fields.
This moderate (1 mile, 1.6 km) trail has rough surfaces and takes you through lava flows and cinder barrens to the base - not to the top - of Sunset Crater. In person, you need water and sturdy footwear. There is also an alternate 1/4-mile (0.4 km), easy, wheelchair accessible paved loop.
Throughout this virtual trail guide, you will find benchmark pages and interpretive station pages. The benchmarks are those numbered in the guidebook, and the interpretative stations are text and photo displays placed along the trail itself.
Life and Landscape Transformed
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.
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.
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.
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.