Name: Sunset Crater
Volcano Type: Cinder Cone
Eruption Status: Dormant
Last Eruption: approximately 1085 CE
Location: 35.3642° N, 111.5040° W,
Northeast of Flagstaff, AZ, USA
Every Volcano Hopper has to get their start somewhere. Sunset Crater was the very first volcano that I was able to get my boots on. You can tell by the picture – I was absolutely giddy about it. And, yes, I bounced up the lava flow like a billy goat.
My partner in crime and I visited in the fall of 2009. We were driving through Flagstaff and I spotted the national monument on the map. I’m not above begging when it comes to visiting a volcano. Luckily, my man has a spirit of adventure too and didn’t hesitate to steer the car north onto Highway 89.
After our visit to the Visitor Center’s museum, which describes the history of the area mentioned in last week’s post, we set out on the Lava Flow Trail. I think my first impression – this being my very first lava flow – was a bit of surprise at how absolutely rugged the lava was. Even after a millenia of being exposed to the elements, the rock was still jagged and sharp. There’s a reason that this type of lava is called A’a (named by the Hawaiian lava flows of similar composition). That’s the sound you make when you walk on the stuff in your flip flops. Ah! Ah! (More like ow, ow, but hey, you get the point).
The lava flow itself was incredibly deep. Thankfully, a trail has been cut through it that makes it easily accessible. Looking back now after some of the other hikes I’ve done over lava, this trail is a cake walk. It really is pretty easy on the legs for the most part, and there’s even a paved section so that anyone can come out and enjoy it. But 1 mile took us at a couple hours since I had my paws into everything.
The trail winds through the Bonito Lava Flow, which flowed downslope and to the west of the actual crater. The lava is made of basalt, which is pretty low in viscosity. That means that it runs quite a bit like honey out of a jar. There are typically 2 types of basaltic lava flows: A’a and pahoehoe (pronounced pah-hoy-hoy). Pahoehoe turn into really cool, ropey formations when it hardens. I’ll talk a lot about that when I get into some of my Hawaiian posts. A’a is the chunky, rough stuff pictured here.
So why the difference? A’a flows are slightly more viscous when they flow, and just slightly cooler. They also tend to really get rocking and rolling when they move down that hill. The outside of the lava tends to cool pretty quickly, but the insides stay hot and keep jamming along faster than a marathon pace. That continued motion, plus the addition of some additional gasses in the lava, cause it to tear itself apart into ragged chunks.
As we start down the trail, the 1000 foot Sunset Crater looms
head of us. Its rim is painted with gold, orange, and red hues that are indeed reminiscent of a desert sunset. These spectacular colors are due to the variety of minerals that were ejected during the eruption, particularly gypsum, silica, and iron oxide. Over the past 1,000 years, oxidation has really allowed some of those colors to shine. The rest of the cone is made up of black and gray cinders. You can see where the wind has blown the loose cinders around; black waves are visible on the slopes.Up close to the crater itself – with a great view of the cinder sides and the sun’s lens flare photobomb. Photo Credit: Volcano Hopper
At the time we were there, the trail to the crater’s summit was closed. I believe it may still be. Early on after word got out that the volcano was in the area, many adventurers, scientists and tourists climbed to the top. Cinder is fairly fragile and can erode easily, so all the foot traffic began to cause the mountain damage. To preserve it’s magnificent conical appearance, the park service has closed off the trail. But there are still plenty of others in the area to explore!
Off to the right as we wandered deeper into the flow, is a smaller volcano called Lenox Crater. It is also a cinder cone, but is barely 1/3 the height of Sunset Crater. Sitting at 300 feet high, it’s easy to miss behind the wall of the lava flow.
So here we have two cinder cones on a single trail, and a whole slew more of them off to the east in what is known as the Cinder Hills. Sunset Crater is actually the youngest of all of the volcanoes in the San Francisco Volcanic Field. So what on earth causes all these cinder cones to form? Glad you asked.
Cinder cones are typically formed when ground water trickles down and mixes with basaltic magma. It turns into a Lava Soup: liquidy and runny, and not nearly as tasty as what Grandma used to make. As the new soup gets closer to the magma below (whether it be the mantle itself or a magma chamber) it heats up in moment and flashes into steam. The steam expands and blows all the rock above it up and out of the way in an explosion. The lava soup splashes out of the new hole. As it cools, the lava forms cinders that pile on top of each other to form a cone. Since the steam opened up a few holes in the ground, that creates an avenue for the magma to bubble up and ooze out over the ground in some pretty spectacular lava flows.
As we wander closer to the mountain, we come across several intriguing features:
During the eruption, gas trapped beneath the surface blew open several more vents near the volcano which allowed more cinder to splash out, causing spatter cones to grow. These guys look like a bunch of volcano mini-me’s.
Semi-cooled lava welled up through some the cracks that formed around the volcano like toothpaste being squeezed from its tube. The lava encountered harder surface rock and created some grooved, wedge-shaped features. These are known as “squeeze ups”.
When the ground cracked open at the start of the eruption, it formed a fissure. Part of that fissure is still intact and is visible from the trail.
Hornitos are upwellings of lava on a lava flow. As lava is flowing, it can tend to back up and create these raised “fingers”. Most of the ones here are now collapsed or damaged from people climbing on them.
While the lava flow did some serious damage when it came down the slope, and it certainly hearty enough to withstand the elements, there is a definite resurgence of life here. Many people focus on the destruction that volcanoes can cause, but they are integral in the circle of life. Volcanic eruptions produce extremely fertile soil which is especially useful for farming. At Sunset Crater and the surrounding area, there are flowers and trees of all shapes and sizes, and wildlife thrives here. Keep your eyes peeled, you never know what you’ll see!
After our hike through the Bonito Lava Flow, we drove to the east side of the volcano and the Cinder Hills Overlook. This provides a spectacular view of the other volcanic features in the area. Unfortunately, we ran out of time on our side-adventure and had to get back on the road. But if you’ve come this far, take the rest of the day and go exploring!
There is more hiking to be done at Lenox Crater and O’Leary Peak. If the Sunset Crater trail happens to be open to the summit, give it a go! Further down the Loop Road, (which is about 35 miles from entrance to exit on Highway 89), you’ll come across the Kana’a Lava Flow. If you look north, you’ll spot Strawberry Crater and it’s lava flow. Further along, you’ll enter the Wupatki National Monument where canyon dwellings and pueblos from the people who inhabited the region are preserved. There are some hiking trails here too for those interested in history and archeology.
If you have the opportunity to go through Flagstaff, take the detour and go check out Sunset Crater. It’s a sight definitely worth exploring. For me, it just fueled the addiction. Once this volcano and I had been aquainted, I certainly wanted to get to know more of it’s volcano friends.
Want to see more pictures? I’ll leave an album for you to browse on my Facebook page.
Want more information on the San Francisco Volcanic Field? Check out this article by the USGS: https://pubs.usgs.gov/fs/2001/fs017-01/
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