The Lava Tubes

"Descend, bold traveler, into the crater of the jokul of Sneffels,
which the shadow of Scartaris touches before the kalends of July, and
you will attain the centre of the earth; which I have done, Arne
Saknussemm." - Jules Verne, Journey to the Center of the Earth

The hike starts normal enough. A well defined path, some rocky spots requiring attentive footwork. But soon you're walking stooped over. You see optional routes. Which one to choose? You're stooping even more, until you're moving forward on hands and knees. More routes are offered. If you're really adventurous, you choose a route where you crawl on your belly. You're in a lava tube. Most likely a maze of tubes. Stay low so you don't bump your head. Remember your route because it's easy to become disoriented - you may be going further into the tube when you think you're heading out. And if you're hiking alone, bring spare light sources, because inside a lava tube it's very, very dark.

The tube began with the eruption of a volcano. The lava flowed downhill. Here and there the sides and top of the flow solidified while the lava inside continued to flow. The eruption ended and the lava ran out, leaving an empty space behind it - the tube. Or, the maze of tubes, as the flows moved in and out of each other, or branched off on their own.

Time passes. The volcano erupts again. The lava tube creation process begins anew. A new level of lava tubes rests atop the previous. The volcano erupts again and again. The landscape becomes honeycombed with lava tubes. One day the roof of a lava tube on the uppermost layer gives way, the rocks hitting the floor in a thunderous crash, and sunlight enters.

Lava Beds National Monument in Northern California contains the largest concentration of lava tubes in North America - more than 700 discovered caves, of which 22 are developed for hiking. The area contains such a variety of igneous features that it attracts geology students (and those with an amateur interest in geology) from far and wide. The lava flows played a role in history. In the 1870s, the Modoc Indians retreated from the Army to this natural fortress. Today one can walk the sites of the Modoc War: where the Army laid siege to the Modoc warriors and their families; where the Modocs almost wiped out an Army patrol; and where the only general in the Indian Wars was killed.

The volcanic activity comes from subduction. The Juan de Fuca and Gorda oceanic plates are sliding under the lighter continental plate. The subduction is creating the Cascade Range which runs from Northern California to British Columbia. (The same subduction process, from a different oceanic plate long ago, created the ancestral Sierra and the granitic plutons of the modern Sierra.) Northern California has several active volcanoes. In my teens I met an elderly man from Tehama County who saw the 1915 eruption of Mount Lassen. The flows in Lava Beds National Monument come from Medicine Lake Volcano to the south. Medicine Lake Volcano, a shield volcano built up one eruption at a time, is the largest volcano in the Cascade Range. An eruption about 1,000 years ago formed Glass Mountain. Yes, a mountain of glass - a massive flow of pumice with large blocks of obsidian. Years ago I walked at the edge of its barren and crunchy surface. Eruptions around Medicine Lake Volcano will continue. The lava tubes so popular with tourists will someday be covered with another layer of lava.

Lava Beds National Monument was created in 1925. During the Depression, the Civilian Conservation Corps developed most of the trails used today. The area had plenty of visitors before this. These visitors did things that would make any park ranger cringe. They dropped rocks and garbage down the Fleener Chimneys vents just to see how far they would fall, until the vents were filled. They removed war artifacts from the battlefields and the grounds where the Modocs stayed under siege. They broke formations off the walls and ceilings of the lava tubes. Today the Park Service rangers enforce the rules that help give the Monument a somewhat primitive feel despite the number of visitors.

I went this past week, in the off season, before school lets out and vacationing families will come in. Many sites in Indian Well Campground were unoccupied.

Oftentimes I was the only person inside a lava tube. I was curious about people getting lost in a lava tube, or stuck in a tight spot. Upon my return I emailed a query to a park ranger about this. Here was the response:

"It is very rare that Lava Beds Rangers have to conduct search and rescue operations in the park. I am not aware of any incidents in which a visitor got stuck nor one in which all light sources failed. Occasionally visitors have difficulty navigating some of the more complex caves (Golden Dome Cave, Labyrinth/Lava Brook Cave System, Hercules Leg/Juniper Cave System). However, they typically find their way out after no more than an hour or two, either on their own or with the help of other visitors. There have been a few instances in which visitors have been lost for an extended period of time (up to 36 hours). Theses incidents have only occurred in Catacombs Cave, by far the most challenging developed cave in the monument."

I did a little more research and found this newspaper article about two school girls lost in Catacombs Cave for more than 27 hours in 2004.

I know how easy it is to get turned around in the maze of tubes. On this trip, I got bewildered in two lava tubes. On a trip many years ago I was hiking out of a tube, only to encounter two others heading towards me who were hiking out of the tube. I had gotten myself turned around and was actually hiking into the tube. And I must admit that, five minutes after realizing I was disoriented alone in a tube, I've had that little bell go off in my head, that "uh-oh" thought.

(Maps of the developed tubes are sold in the Visitor Center, but a map would take the adventure out of my exploration.)

And there are the low spots. On this trip I didn't go anywhere requiring more than a deep crouch. But years ago, in what tube I can't remember, I was walking along, the ceiling getting lower and lower, the walls perhaps fifteen feet apart, until I reached an area where the ceiling height was slightly under waist level. Not a tight squeeze by lava tube standards, with some openings one foot high. I shined my flashlight down the tube. I saw that the ceiling remained at this height for some twenty feet, and then it rose to where I could walk upright. The floor of the tube was smooth. I removed my daypack and got on my belly. I cradled the daypack strap in one elbow while holding my flashlight in my other hand, and I crawled through that opening. The ceiling rose and soon I was upright, and I continued on. I did this alone. I don't think anyone else was in the tube.

Those with the proper training and equipment take on the undeveloped lava tubes. For us casual visitors, the developed tubes in Lava Beds National Monument offer a pleasant little adventure.

Natural Bridge Cave, with my truck

Sunshine Cave

A small opening in Hercules Leg Cave

Balcony Cave

Boulevard Cave, another small opening

Loch Leven Trail

Temperatures in the nineties in the Sacramento Valley are driving hikers to higher elevations in the Sierra. Today I hiked a very popular trail, the Loch Leven Trail, which starts near Interstate 80, at an elevation of 5,680 feet. I arrived early, before eight o'clock, to avoid the crowds, and only a few vehicles were in the small parking lot. When I returned a few hours later, the lot was full and vehicles were parked in any available space nearby.

The trail was covered in snow just a few weeks ago. Patches of snow were still about. Water from snowmelt ran down some sections of the trail. Several large trees felled by the weight of snow over the winter lay across the trail. They will eventually be cleared.

The elevation gain is only 1,070 feet. The rocks and tree roots on the trail add some difficulty to the hike, particularly on the descent. There is a bit of scrambling in places. A hiking staff helps with stability.

The geology is interesting. The trail crosses the boundary between two rocks. The rock in the Rattlesnake Creek Pluton is granodiorite, a relative of granite, and is 120 million years old. This rock intruded as magma into the older Jurassic volcanic arc rock (Early Jurassic, about 200 million years old) during a subduction process. This pluton was essentially a large blob of molten rock that moved upward from the subduction zone far below. The magma followed fractures and melted overlying rock. Some magma reached the surface and erupted as volcanoes. But most stayed five to ten miles underground in a large chamber, and slowly cooled to leave the crystals in the rock we see today.

Where I stood on the granodiorite, the rock went several miles below me, and it once went several miles overhead. What eroded came to rest in what is now the Sacramento Valley.

There is no distinct line between the Cretaceous granodiorite and the Jurassic terrane rock. The two slowly melded together until one gave way to the other.

I continued up the trail, crossing the railroad tracks, the original ones being built by the Chinese for the Transcontinental Railroad. Further up I encountered snow. I scrambled about trees fallen across the trail. I passed granodiorite outcrops polished and scraped by glaciers. I passed the first two Loch Leven lakes and had lunch at the third.

 

A wonderful day in the Sierra.