Arizona’s Youngest Volcano Erupted Just 940 Years Ago & You Can Hike Its Lava Field

Sunset Crater, Arizona

In 1085 CE, a massive fissure ripped open near what is now Flagstaff, Arizona.

The eruption shot lava fountains 2,000 feet high and ash clouds over 12 miles into the sky, forcing ancient people to abandon their homes.

Here’s what happened during that year of fire, now protected as Sunset Crater Volcano National Monument.

Warning Tremors Before The Explosion

The ground shook for days with increasingly strong earthquakes before the eruption. Sinagua farmers living nearby felt these tremors grow more intense as magma pushed upward. Families packed up and left their homes and corn fields as the shaking continued.

The Six-Mile Fissure Opens

The eruption began when the ground split open along a crack nearly six miles long. Hot magma and gases pushed through this giant fissure with explosive force.

Volcanic fragments shot into the sky along the entire crack, creating what scientists call a “curtain of fire.” Small cinder cones started forming at several points as erupted material fell back to earth.

Soon the volcanic activity focused at one spot that grew into Sunset Crater itself.

The Massive Eruption Plumes

The volcano produced at least five major explosions during the main eruption. Each blast sent huge columns of ash and gas 4 to 19 miles into the sky.

People throughout Arizona and into New Mexico could see these dark towers rising above the landscape. Scientists now recognize this as the most powerful cinder cone eruption ever documented.

Lava fountains shot hundreds of feet upward in a style called Strombolian eruption. These fountains continued much longer than normal for this type of volcano, helping build the massive cone.

Birth Of The Bonito Lava Flow

Hot lava broke through the western base of the growing cone, creating the Bonito Flow. This molten rock traveled northwest about 1.6 miles before cooling completely.

Older volcanoes surrounding the area trapped the flow, causing lava to pool up to 100 feet deep. The Bonito Flow formed during at least three separate surges of lava.

Near the eruption vent, lava cooled into smooth, rope-like formations. Further away, it formed rough, jagged surfaces as the flow slowed and cooled while still moving forward.

The Kana’a Lava Flow Forms

Another lava flow burst from the eastern side of Sunset Crater, creating the Kana’a flow. This river of molten rock traveled 6 miles northeast, permanently changing the landscape.

Like the Bonito flow, Kana’a had smooth surfaces near the vent and rough terrain further out. Scientists found that most of the Kana’a flow formed during the main explosive phase.

While Bonito continued growing during later eruption stages, Kana’a largely finished earlier. Both flows transformed pine forests into black, rocky terrain where plants could not grow.

Widespread Ash Blankets The Land

Ash and small volcanic fragments covered more than 810 square miles of northern Arizona. Wind carried lighter particles far from the volcano, with thick deposits reaching 15 miles away.

The eruption spread material across forests, fields, and villages. In total, the volcano ejected enough material to fill 173,000 Olympic swimming pools.

Ash depth varied across the region. Areas closest to Sunset Crater received thick layers that buried everything, while distant locations got a lighter dusting that changed the soil.

Sinagua People Flee Their Homes

The eruption forced between 1,000 and 5,000 Sinagua people to leave their homes. Families abandoned villages as ash and cinders made survival impossible near the volcano.

Any area covered by more than 6-8 inches of ash became useless for growing food. Many refugees moved to lower elevations around Wupatki, northeast of the volcano.

These displaced communities had to adapt their farming methods to new environments. The migration changed settlement patterns across northern Arizona as people rebuilt their lives in safer areas.

Ritual Offerings During Eruption

Some brave Sinagua people approached active lava flows carrying ears of corn as offerings. Archaeologists found 55 pieces of lava with corn kernels and husks impressions preserved in stone.

They placed corn near small vents called hornitos that formed above lava flows. Hot lava covered the corn and cooled quickly, creating detailed impressions in rock.

These “corn rocks” were found in homes more than 2.5 miles from the nearest lava. This shows people carried these objects back to their villages, possibly as sacred items connecting them to the volcano.

Final Waning Eruption Phase

The volcano’s activity gradually decreased in its final stage. This waning phase produced smaller, disconnected ash deposits containing much less material than earlier explosions.

The last cinders contained high iron content that turned red when exposed to air, creating the reddish cap that gives Sunset Crater its name. Scientists believe the entire eruption lasted less than a year.

Some research suggests the main activity might have ended in just a few months. After erupting, Sunset Crater became permanently dormant, as this type of volcano erupts only once.

The Volcanic Ash Mulch Effect

Areas covered by thin ash layers—less than 6 inches deep—experienced unexpected benefits. These volcanic cinders worked like mulch, helping soil hold moisture in the dry climate.

Previously poor farming land became productive, especially around Wupatki. Sinagua farmers returned within years, using these new ash-covered soils.

Population grew rapidly in the decades following the eruption. Communities built larger villages throughout the region as farming improved on the ash-enriched lands, turning disaster into opportunity.

Visiting Sunset Crater

You’ll find Sunset Crater Volcano National Monument at 6400 U.S. 89, Flagstaff, AZ 86004, about 20 miles north of downtown.

The monument is open 24 hours daily, with the visitor center operating from 9:00 AM to 4:30 PM.

Don’t miss the one-mile Lava Flow Trail where you can see pahoehoe and a’a lava formations, squeeze-ups, and hornitos created in 1085.

Entrance costs $25 per vehicle, $15 for pedestrians/cyclists, valid for seven days and includes access to nearby Wupatki National Monument.

The 34-mile scenic loop drive connects both monuments, taking you from volcanic landscapes to ancient Sinagua dwellings where people relocated after the eruption.

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