Into the Caves
"California's Underground" at the Oakland, California Museum
by Stuart Sweetow
All Photos Courtesy of the Oakland Museum of California

I squeeze through a tight opening and enter a world of darkness. I think my eyes will adjust to the light, but there is no light. I rely on my hands and feet to guide me through this mysterious labyrinth to the promise of a visual cornucopia of mineral delights.

As I weave through this maze, wondering if I will bump my head or step into a deep chasm, I see a light at the end of the tunnel, literally. Could this be the headlight of the miner whose song echoes through these cavern walls as I make my journey through the darkness? Will I get a chance to stretch my arms before claustrophobia strikes?

Pristine marble cave chamber. Photo by Dave Bunnell.

The light is one of many spotlights illuminating cave exhibits at the Oakland Museum of California. This museum devotes its exhibits to the environment, history and art of California. "California Underground" is a family-oriented cave exhibition running through January 9, 2000.

In addition to the simulated cave entrance I squeezed through, other exhibits include a junior speleologists' section, a growing stalactite, an interactive crawlspace and a hands-on cave photography exhibit. Visitors hear the songs and stories of miners piped through loudspeakers, and examine the dramatic photographs of stunning cave formations that grace the halls.

Children explore the challenge of moving through caves without breaking the fragile formations. They crawl among simulated stalactites that buzz when touched in order to teach them this skill.

In an interactive exhibit called "How Flat Can You Go?" little visitors slide belly-down into an opening that measures your size so you will know the minimum clearance you will need to squeeze through tight cave openings. It also lets you know if you are claustrophobic.

My guide, Christopher Richard, the curator of this exhibit, tells me that cavers need to deal with two human frailties: fear of constriction and fear of the dark. An experienced caver himself, Richard loves the dark but admits some "anxiety [in] tight places." He says an exhibit such as this provides self-awareness that leads to more confidence for would-be cave explorers.

The "Cave Gear" exhibit not only shows the type of clothing and boots that cavers should wear. It also emphasizes that at least one person in your party should survey the cave and draw a map. Not only will these precautions help future explorers in your cave, they may also be your only guide for getting out safely!

The exhibit identifies the three light sources cavers should carry: a helmet light, a flashlight and a safety light (a candle or Glowstick). Don't forget to take extra batteries and bulbs. Old boots, thick socks and dirty coveralls are the suggested attire for this affair. Oh, and by the way, wear long underwear; caves can get damp and chilly.

Other helpful cave supplies include a space blanket or trash bag for warmth, energy bars, water, a whistle, rope, compass, and if you plan to travel vertically, a rappelling rig.

How Caves Are Formed

At left, a multilevel lava tube in the "California Underground" cave exhibit at the Oakland Museum. Photo by Peter and Ann Bosted.

While this exhibit includes the standard limestone and marble caves, California's caves are as diverse as her population. Visitors to the museum learn about sea caves, mud caves, lava tubes and wind caves.

The exhibit called "Fire and Ice" shows how lava tube caves form in the wake of fiery volcanic eruptions. Molten lava flows beneath cooled, hardened lava and forms levies that channel the flow. The fluid lava sometimes splatters to form arches. The stalactites and stalagmites in lava-tube caves come from water that trickles in from snowmelt. Lava tubes can form in as little as a week, but last thousands of years.

The more common limestone caves take tens of thousands of years to develop. Groundwater carrying dissolved calcite form them. The CO2 in the water releases dissolved rock and redeposits it as stalactites and other flowstone formations. A travertine cave is similar to a limestone cave but, in this case, the dissolved calcite is deposited as flowstone at the mouth of a spring.

Stunning photographs at the museum showed flowstone "draperies," where rivulets of calcite-laden water flow down an incline. Another photograph showed what cavers call "bacon": draperies with bands formed by colored impurities.

While limestone and lava-tube caves last thousands of years, sea caves formed by the pounding surf erode away after roughly 500 years. Interestingly, the constant pummeling of the rocky shore is responsible both for the formation and the decay of sea caves.

Through photos and charts, the museum exhibit demonstrates how, at the end of the Ice Age, California's rocky coast contained cracks, faults and soft regions. The water found its way into these openings, and erosion proceeded to form the many sea caves that now dot the California coastline.

I learn that smugglers throughout the years hid their loot and sometimes themselves in these caves. I also discover that these caves can be death traps due to rising tides or larger waves.

Displays show various types of caves and how they form. The "Slip and Slide" exhibit shows how gravity commonly forms caves. Over thousands of years, streams and glaciers cut away at the Earth's crust and form deep slots in the rock below. This, coupled with the slow creep of gradually sagging clay beds and landslides that develop from rock slabs, creates some of the spectacular caves.

Mud caves form through the action of large streams that run under canyons and cut into the hard, insoluble granite bedrock. Talus caves come from layers of rocks and boulders that slip down and arch over canyons.

In an exhibit entitled "Wind and Rain" museum visitors see photos of a soil-pipe cave in Death Valley. Glacier melt percolates downward through soft sediments. A hard layer stops the water, and pressure builds. The pressurized water flows to the face of a cliff, taking sediment with it. A detailed photo shows an upper layer of a basalt lava cap and a lower layer where groundwater washed out the sediment.

Nearby are photos of wind caves. Moisture that persists on the shady side of sandstone dissolves the stone to sand grains. The loosened grains blow away, leaving a shallow wind cave.

Mining and the Environment

Visitors are treated to an exhibit showing soapstone fragments that tell the story of the Cabrielo Indians on Catalina Island in about A.D. 1200. They developed a quarrying and carving enterprise, using soapstone mined from a local cave. Over the years, this tribe produced several implements and developed a business supplying soapstone materials.

At right, a delicate aragonite flower. Photo by David Bunnell.

In this modern age, the fragile environment of caves has become a concern to such groups as the National Speleogical Society. As part of an exhibit called "Cave Conservation," visitors learn that the society asks that cavers not collect mineral or biological specimens in caves. Caves provide a protected environment for some animals, and disturbing the environment could upset nature's balance, such as awakening hibernating animals.

The exhibit includes startling photographs of vandalism, litter and graffiti in caves. Even careful cavers leave muddy footprints, which build up over time, staining the fragile formations. One photo shows a respectful caver who removed his boots before traversing delicate rock.

The exhibit stresses that the outside environment has not harmed these exquisite caves for thousands of years. Minor carelessness on the part of people going inside the caves can have a serious effect. Some of the photos in the exhibit show cavers who go into caves and fix broken stalactites with epoxy. Another caver cleans mud off cave formations.

Richard tells us that California is home to about 3,000 caves. Only a handful are "show caves"--i.e., those open to visitors. The whereabouts of most caves are known only to the Speleogical Society. This is to ensure that no one and nothing jeopardizes these caves' centuries-old formations.

Caves as Habitat for Plants and Animals

It is well known that caves are safe havens for hibernating bears. In addition, however, caves are home to several species of animals that thrive in the darkness. Nature has adapted bats particularly well to the dark environment of caves. The museum exhibit includes an elaborate section on those sightless flying mammals. One interactive display explains how bats' navigation vocalization works. Another demonstrates sound vibrations. A third display lets visitors measure just how high a frequency the human ear can detect.

The "Bucket o' Bugs" display demonstrates the huge amount of bugs that bats must eat each day. It includes a scale where visitors can weigh themselves. The scale shows how many buckets of bugs they would have to eat if they were bats, based on their weight relative to that of bats. I learn that I would have to eat 95 buckets of bugs a day, if I were a bat!

Other cave inhabitants include spiders, millipedes, moths, snails, red-tail foxes and owls. The damp darkness provides a good environment for growing mushrooms. Where slivers of light creep into some caves, occasionally some species of fern will even grow.

Cave Formations

At left, a curtain of stalactites in a limestone cave. Photo by Dave Bunnell.

Breathtaking photographs show some of the amazing formations found in caves. Where powerful flows of sandy water scoured the walls of caves, these walls now look like beautifully polished marble. Other photos demonstrate how various stalactites, stalagmites and other formations develop. Soda-straw formations start with calcite-rich water flowing through hollow tubes. When the tubes become plugged up, the water flows outside the tube, forming a stalactite.

Helictites also come from calcite solutions. These are irregular, capillary-sized tubes. A photo shows pool spar, made of calcite crystals formed underwater. Other underwater photograph shows cave pearls. These grow in shallow pools of calcite-rich water. Cave pearls result from the agitation of dripping or flowing water.

A simulated cross section of a cave depicts a limestone labyrinth of channels formed as water dissolves rock. The water redeposits the dissolved minerals, forming stalactites and other delightful creations. This display shows how water can sculpt an internal environment.

Growing a Stalactite

One of the most exciting exhibits at the museum is the demonstration of growing a "live" stalactite. Stalactites grow from the CO2 in water, that carries dissolved limestone. When exposed to air, the CO2 is released into the atmosphere, the pH rises and calcite precipitates out. Stalactites grow at the rate of about 1 inch a century.

Since the Oakland Museum needs to dismantle this exhibit in January 2000 (This particular exhibit "California Underground: Caves and Subterranean Habitats," continues through September 12, 1999.), the staff members felt a need to speed up Mother Nature's normal process. The stalactite growing here is because of calcium hydroxide dripping into a CO2-rich atmosphere. At the time of this writing, the 6-inch stalactite represented a growth rate of about 2 inches per month.

Cave Photography

At right, calcite drapery and stalactite. Photo by Dave Bunnell

One thing you can take in caves are pictures. An exciting, interactive exhibit lets visitors create their own "photos" of a simulated miniature cave. The exhibit places nine lights in different portions of this diorama. Visitors push different buttons to activate different lights in the cave.

Since most caves are totally dark, you can mount your camera on a tripod and leave your camera's shutter open as you move a flash unit around different sections of the cave. The exhibit demonstrates the effect of flashes on different sections. A direct flash illuminates foreground objects, but you can achieve a dramatic, transparent look by using backlighting. A fill-light balances outside light with your flash.

The cave-photography exhibit shows how to paint with light so you can produce some spectacular photos the next time you visit a cave.

Awakening From the California Dream

"Penn Mine Toxic Pits" is a sign depicted in a photograph at the Oakland Museum. It is part of a photo exhibit that examines changes in California's environment over the past 150 years and the way these changes relate to the state's social history.

"The Price of Gold" is the title of a series of photographs about the spoiled land left in the wake of the Gold Rush. The descriptive text reads, "Hydraulic monitors and dredging machines slashed wounds in the land and sent mud downstream to shoal San Francisco Bay. Mercury and other toxins entered the state's waterways."

The photographs and interpretive panels take visitors through time, from a California of pristine natural beauty to an era of damage inflicted by mining, agriculture, energy production and urbanization. "California used to have rivers [teeming] with salmon, and lakes rich with otters and beaver. All of this began to change in the late 18th century, and much was swept away after the discovery of gold in 1848."

In the series of photos entitled "Alabaster Cities," visitors see houses built on old farmland, shopping malls dependent on the automobile and evidence of cities built without plans. These "alabaster cities grew without bounds and are resistant to traditional ideas of community."

We see a photograph of a sign proposing a nuclear waste dump close to the Arizona border--evidence of the near-extinction of salmon and of soil changed by new farming practices.

This compelling photo exhibit asks visitors to weigh the value of what we have gained by "progress" compared to the loss of land "now largely forgotten." It concludes with "Alternate Courses," showing photographs of people restoring creeks, planning cities and groups working to reverse environmental crises.

Museum admission is as follows: $6 for adults, $4 for seniors, students and children six and over. Children under six are free when accompanied by an adult. Oakland Museum members are also admitted free.

The Oakland Museum of California is at the corner of Oak and 10th streets, in Oakland, one block from the Lake Merritt BART station. From I-888, take the Oak Street Exit and turn right. Call the museum at (888) OAK-MUSE. The Oakland Museum of California web site URL is

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