Science, whether conducted indoors or outdoors, requires some safety precautions. For example, scientists use gloves and safety glasses when using chemicals in a laboratory. A forester may use safety glasses, a hard hat, and boots when working outside in the forest (figure 1). Before starting any activity in science, scientists first evaluate whether they need special equipment to ensure their safety.

The scientists in this study conducted their research in a cave. They needed safety gear specific to the cave environment, such as warm clothes, hard hats, gloves, headlights, and boots. As you read this article, remember to look at the photos of scientists in caves. What safety equipment are they wearing?

Safety, however, is more than just about equipment. Good communication also is important to safety. Whether inside or outside, scientists must communicate when, where, and how they are conducting an experiment. To safely conduct the study described in this monograph, the scientists needed to communicate where and when they were going into the cave. This basic information ensured that the scientists could be helped if a problem occurred.

Water moves through and across Earth in a cycle, called the water cycle (figure 2). Water can change as it moves through the water cycle. Water may change forms between a liquid, a solid, and a gas.

Water also can change when it interacts with chemicals within the environment. For example, interactions between water and chemicals can result in the development of caves. Many caves in the United States are formed when groundwater or rainfall absorbs carbon dioxide. The combination of water and carbon dioxide forms carbonic acid, which is slightly acidic. Over time, the water enters cavities in the rock and slowly dissolves the cavities creating larger open areas.

This process also contributes to the formation of speleothems (figures 3a-3c). The slightly acidic water moves through rocks, dissolving calcite. The water has large amounts of carbon dioxide in it when it enters the cave. The cave air, however, only has a small amount of carbon dioxide, so some or all of carbon dioxide from water is released into the air. This process is similar to when you open a can of soda and the carbon dioxide creates bubbles as it leaves the liquid. The calcite is unable to stay in the water without carbon dioxide, so it is deposited onto cave floors, ceilings, and walls forming speleothems.

The scientists in this study found many different speleothems during their research, including large shields, rimstone pools, folia, spar crystals, curtains, and helictites. Some of the speleothems grew so large that they affected the movement of water and sediments through the cave. Speleothems illustrate a portion of the water cycle, as well as how chemicals, like calcium, cycle through the environment.

Caves are important natural features in Sequoia and Kings Canyon National Parks in California (figure 4). Past studies of caves in the area have focused on two of the largest caves, Lilburn Cave and Crystal Cave. Studies of these caves revealed information about the area’s mountains, the formation of caves, and the age of rocks.

Another large cave in the area is Hurricane Crawl Cave. Hurricane Crawl Cave was first explored in 1988. Scientists mapped the cave’s approximately 2 miles of passages between 1988 and 1995. The cave has two entrances, multiple levels, two canyons, two mazes, and one large room (figures 5).

The main stream that passes through the cave is a sinking stream. This stream starts on Earth’s surface, enters the cave for a period of time, and then returns to Earth’s surface further downhill (figure 6).

The scientists knew that Hurricane Crawl Cave developed under similar conditions to Crystal Cave because they are located near one another. However, the scientists noted that Hurricane Crawl Cave had a different morphology, or structure, than Crystal Cave. Crystal Cave has many levels and mazes, but few canyons. The scientists wanted to know why the morphology is different between Hurricane Crawl Cave and Crystal Cave.

To better understand Hurricane Crawl Cave, the scientists collected data regarding the cave’s age. A previous study estimated the age of a rock from inside Hurricane Crawl Cave. From the rock’s location, the scientists measured to the top of the cave and to the bottom of the cave. These measurements enabled them to estimate how long it took for the cave to develop both before and after the rock was deposited.

The scientists also collected information about the past and present movement of water through the cave. Current information about the flow of water was gathered between 2010 and 2012. Specifically, the scientists measured water discharge. The water discharge measurements were taken twice per year at the same location inside the cave, once during June and once during October (figure 7).

The scientists also conducted a dye trace (figure 8). A dye trace involves putting a non-harmful, colored dye in water. Scientists then track and observe the dye to understand the movement of water. Previous research indicated one stream that passed through the cave. In this study, the scientists used a dye trace on multiple streams to confirm if any other streams passed through the cave.

The scientists then chose four transects within Hurricane Crawl Cave to collect data about past water discharge (figure 9).

Information about cave scallops and stream cobbles were collected at each transect (figures 10 & 11). You may have heard of animals called scallops, which live in the ocean, but cave scallops are nonliving. Cave scallops are asymmetrical, scoop-like formations on cave surfaces formed by water. Scallops can indicate the direction of water flow and the velocity of water. Stream cobbles are rocks that are carried in the flow of water. A mathematical formula enabled the scientists to determine the velocity of water needed to move the stream cobbles. A total of 327 scallops and 157 stream cobbles were measured across the four transects.

The scientists’ observations, combined with the estimated age of the rocks, indicated that Hurricane Crawl Cave is approximately 1.4 million years old. Recall that the scientists also wanted to compare past and present water discharge in the cave.

Scallop measurements at the four transects indicated that the direction of water flow is similar between the past and present. Scallop measurements and stream cobbles both indicated that past discharge of water was greater than current discharge (table 1 and figure 12). Past discharge did not vary across the four transects. Instead, past discharge varied by passage type. Specifically, the wide, upper passages of the cave had very high discharge in the past.

When the scientists completed the dye trace, they found that one sinking stream could be traced through the cave. This finding confirmed previous research results. However, they also found other streams that began in the cave.

The scientists determined that Hurricane Crawl Cave likely formed under two different conditions over the past approximately 1.4 million years. First, the wide, upper passages were formed at a time when the cave passages were full of water. The slightly acidic water sloshed like water in a pool, slowly enlarging the passages. Second, the narrow parts of the cave, like canyons and mazes, were formed as water moved downhill under the influence of gravity. The slightly acidic water and the stream cobbles also helped to enlarge the passages. This condition is most similar to what is occurring in the cave today.

In both of these past conditions, the highwater discharge was likely because climate conditions were different than current climate conditions. Past climate was cooler and wetter than at the present.

Although Hurricane Crawl Cave and Crystal Cave are located near one another and developed under similar conditions, their morphologies differ. The scientists concluded that the differences in morphology are likely a result of differing amounts of sediment transported through the caves.