LAVA TUBES AND PITS

Over 400 volcanoes and a veneer of lava flows, known to geologists as the San Francisco Volcanic Field, cover an area fifty miles long and thirty miles wide around Flagstaff. There are places in the lava flows where a crust formed over molten rock which then drained away and left hollow tubes and pits. Some of this cavities have collapsed and been found and certainly others have not. In addition underneath all that lava is the Kaibab Limestone where caverns tend to form.

Lava River Cave

The best and most famous lava tube in the state of Arizona is Lava River Cave, originally known as Government Cave. It is three-quarters of a mile long, in places thirty feet in diameter and splits into two smaller tubes then rejoins. The roof caved in long ago in such a way that it revealed the upper branch of the cave but large boulders blocked the downhill rest of the cave. How far the downhill branch may continues is unknown.

It is truly a marvel among lava tubes. There are 11,000,000 hits about it on the internet and a deluge of photographs. I don't think it necessary that I go into in depth here, pun intended. I have been to it a dozen times since I was a teenager and never taken a decent photo of it. The photos I have included here I plucked off the internet.

The roof collapsed to reveal an entrance to Lave River Cave

The tube splits into two smaller ones then rejoin.

For a lava tube to form the eruption stops and the still fluid molten rock drains out by gravity or the vent sucks it back down into the earth or both. In any case a hike into Lava River Cave is well worth the geologic adventure.

There is an element of risk. There is ice covering the rocks just inside the entrance even in the summer. It is a rock scramble for the first hundred feet or so and loose rock litter the floor in some places. There is an ever present danger of rock slabs falling from the ceiling although none have been known to since its discovery in 1915.

Wear warm clothes, boots and take two flashlights per person. Its location is 14 miles out Highway 180 towards the Grand Canyon. Turn left on Forest Service Road 245 for six miles. Turn left on FS 171 for one mile. Turn left on FS 171B and it's .4 miles to the cave. This is a popular place so don't expect a private experience.

Scholz Lake Lava Tube

Scholz Lake was formed when an earthen dam was built most likely around 1916. The U.S. Government contracted for hundreds of ponds and lakes to be created on federal lands all over the southwestern states. This encouraged ranchers to raise herds of cattle to feed the Allied troops fighting in Europe during World War I.

After the dam was built snow melt and rain water flowed into the lake but it only reached a shallow depth and wouldn't fill. Engineers found a lava tube at the far end of the lake where the water was draining out. A sizable pile of drift wood had plugged the entrance but not tight enough to stop the flow of water. They had to built a second damn as a berm surrounding the mouth of the lava tube so the lake could fill.

A grass covered berm surrounded the entrance to the lava tube.

I paddled my kayak around the lake and saw the earthen berm but couldn't tell why it was there. I didn't want to get out of the kayak because the mud along the shore was so deep and sticky. The next time I went to the lake I walked the 2.8 miles around it so I could see what was behind the berm.

The berm with the lava tube to the right.

Boulders had fallen down partially hiding the entrance to the lava tube.

The entrance was completely plugged by drift wood.

Looking at the berm and lake while standing over the cave entrance.

How large the lava tube is and how far it back it goes is unknown. It would take a huge effort to remove the driftwood.

Sunset Crater Lava Tube

There is also a lava tube at Sunset Crater but it was barred in 1973 because the ceiling was in danger of collapsing. Aren't they all? I crawled into it in 1962 but had no light so I didn't go far.

The entrance to the lava tube at Sunset Crater is permanently barred.

There is a nature walk through the park on the North and South Lava Trails where you can see other volcanic features such as the Bonito Lava Flow, lava blisters and spatter cones.

Paradise Forks Lava Tube and Collapse Pit

Southwest of Flagstaff halfway to Williams is Paradise Forks, a popular rock climbing area. It is at the head of Sycamore Creek which has cut deeply into thick lava flows exposing the vertical shrinkage cracks that climbers enjoy.

Opposite the climbing walls on the other side of the canyon is a plugged lave tube. Sometimes as lava cools it thickens into a blocky flow called a'a that can't drain out of the tube. It solidifies into a plugged tube of poorly consolidated rock. If erosion exposes the tube it may be recognized as a circle of noticeably different rock that crumbles faster than the surrounding denser lava.

A plugged lava tube erodes faster than the surrounding rock.

On the south side of the canyon, a quarter-of-a-mile past the climbing walls is a collapse pit 200 feet across and 50 feet deep. This was a lava cauldron that started to cool and formed a solidified cap. Then the molten rock either drained or was sucked back down into the vent and left a cavity hidden beneath the hardened cap. It held suspended for a few million years before it collapsed in the last few centuries. The jumbled rocks in the pit have not formed the rusty colored coating like the far wall has, indicating it hasn't been exposed to oxygen and moisture very long.

Collapse Pit

Lava Tube 231

I was driving on Woody Mountain Road 231 when I noticed this depression in the ground next to the road so I stopped. At the base of the rock ledge I found a hole that appeared to be an opening into a lava tube. There was a strong flow of cold air coming out the hole so I thought it must lead to a sizable cavity. It is on the right side of the road a little more than a mile past Rodger's Lake.

Lava Tube 231

Standing in the opening.

Each leg of the triangle is about 18 inches long.

The hole is too small for me to fit through so I told a spelunker friend of mine about the opening I had found. He did squirm into it and found a lava tube but since he was alone he didn't explore it.

Arrowhead Sink

Arrowhead Sink is a limestone sinkhole that formed underneath a thick lava flow. The roof of the limestone cavern and lava cap both eventually collapsed creating a hole 130 feet deep. At the base of the lava flow are three lava tubes. All three are plugged but one is a cave about fifteen feet deep that was used as shelter by Native American Indians.

Arrowhead Sink and the 1st lava tube on the right.

1st lava tube is plugged.

2nd and 3rd Lava tubes at the base of the rock wall.

The tube on the right goes back 15 feet and has smoke stains on it's ceiling. NA612 is written in white paint on the rock over the cave. I assume it is an identifier as an archaeological site which has already been excavated. No artifacts remain in the cave.

Cave NA612

The I-17 Lava Tube

A lava tube was exposed in the 1970's when the road bed for the I-17 freeway between Flagstaff and Camp Verde was being excavated. Drillers were boring holes to set explosives when the drill bit punched through the ceiling of a lava tube.

The contractor thought it necessary to cover the opening behind a concrete barrier which you can see today as you zip past at 75 miles-per-hour. In the same road cut there are two other lava tubes that didn't drain but still left a small gap at the top of the tube.

The intense heat of the molten lava melted the ceiling which dripped and
formed small stalactites like frozen 'rocksicles' hanging from the ceiling.

Angular rock shards on the floor were blown in when the hill was dynamited.

Over the centuries a layer of calcium carbonate precipitated onto the floor of the tube.

The road cut with the lava cavities is located at mile 306.5 in the south bound lane north of the Stoneman Lake Exit. If you pass this sign heading south you've gone too far, the road cut is behind you.

San Francisco Wash Lava Tube

The opening to lava tubes sometimes made attractive homes for Native American Indians in the past. This small pueblo is in the mouth of a lava tube in the San Francisco Wash east of Flagstaff. The Indians used the lava rocks to build the walls of the dwelling.