Reliably Warm & Consistently Cool

Why doesn’t the cave’s temperature change daily, or with the seasons like it does outside?

A cave’s temperature is generally equal to the average temperature of the surrounding area, meaning that caves in different parts of the world, at different elevations, will have different temperatures. A cave receives its temperature from a number of “inputs” including air and water flow, as well as direct transmission through the rock walls of the cave, but this is an incredibly slow process.

Rock has a very high thermal mass (this is the rock’s ability to absorb and store heat energy) and it acts like a big blanket the prevents the cave from absorbing or giving away heat. Rat’s Nest Cave is literally inside a mountain, so there is a whole lot of rock between the cave and the outside air. It takes either a lot of temperature difference, a lot of time, or both to influence the temperature of the cave which is why changes in the cave usually occur over hundreds or thousands of years.

Sometimes it can feel colder in some parts of the Rat’s Nest Cave than others. This can be the result of air flow, or “breathing,” that occurs in parts of the cave because of a temperature or pressure difference.

Even though Rat’s Nest Cave only has one known entrance, we are quite confident that there are other smaller holes that allow air to enter or escape and these holes are likely present at different elevations. Cold winter air entering a lower hole might warm and rise through the cave to exit higher up, drawing more air in - while in the summer warm air can cool and sink down through the cave. High and low pressure systems can also influence the flow of air into and out of the cave.

This predictably slow change in temperature means that caves are an incredible repository of historical temperature data. In theory, if you travel to a part of a cave deep inside a mountain that has minimal air and water flow, the temperature you are feeling could actually be thousands of years old as the cave has not yet adjusted to modern temperatures.

Caves offer even more interesting ways to measure past climate information, and they come in the form of beautiful mineral decorations collectively known as speleothems.

You are most likely familiar with the speleothems known as stalactites and stalagmites. These are two of many types of cave formations created as a result of the mineral calcite being deposited by drip water as it runs down the walls of caves. Stalactites, stalagmites, and all of the other speleothems have become some of the most important sources of climate data in the discussion around climate change due to their global ubiquitousness (caves are everywhere in the world) and their unique ability to store information over long periods of time.

The way these beautiful little formations store information is fascinating, and temperature is just one of the stories that is captured. For example, due to the fact that speleothems form from the flow of water we know that if the surface temperature is cold enough to prevent water from entering the cave these formations will stop growing. We can see these cold events (aka glaciations) in the speleothem record.

As water travels down from the surface and into the cave it is bringing organic chemicals along with it. These organics are trapped in the calcite mineral, and because these organics are only available when plants are growing we can track the seasonal growth of plants. We can even see sun activity oscillations in the deposition of certain chemicals.

The most promising feature of these formations is their propensity for trapping gasses in the minerals during the formation process. Some of the oldest formations in Rats Nest Cave are over 750,000 years old meaning that we have gases trapped in formations that are that old as well. This gives us the ability to directly compare those gases with their modern counterparts, providing insights into those past climates. Enthralling stuff!