Caves & Karst

Although these pages do give some background on caves in the Canadian Rockies, the Alberta Speleological Society does not provide cave entrance locations to the general public, for safety and conservation reasons.

Caves and Karst of the Canadian Rockies

Limestone, dolomite, marble and gypsum are types of bedrock that are slightly water-soluble. Landscapes that have water-soluble bedrock will, given enough time and the right conditions, look quite different as rock is dissolved away. These are called karst landscapes and include distinctive surface features as well as underground caves and watercourses.

Limestone abounds in the Canadian Rockies, which is good news for both cavers and karst geologists and hydrologists.

There are numerous books, other publications and on-line sources about caves and karst; however for a good, concise overview in an Alberta Rocky Mountain context, we recommend the book: Under Grotto Mountain: Rat's Nest Cave, Charles M. Yonge, 2nd ed., 2012, ISBN 978-0-9879369-2-9.

Flop Pot

Limestone Cave Creation

Dating of formations in Canadian Rockies caves typically provides figures greater than 350,000 years and often >1.3 million years (Yonge 1989). Caves form at, or beneath the water table. Mineral formations are created later, in a depositional phase, following a lowering of the water table. Thus we know that most larger caves are much older than the mineral formations they contain. The solutional processes by which caves are formed consist of a number of chemical reactions between meteoric waters and calcium carbonate, the dominant mineral which forms limestone.

“The carbon dioxide combines with water to produce carbonic acid, which in turn attacks the calcite and divides it into soluble ions. A cubic meter of water exposed to air containing 10% carbon dioxide, if kept in contact with limestone until the reaction ceases, can dissolve about 250 grams of calcite”. (Moore and Sulivan 1978)

The limestone removed in producing a cave is the end-point of a complex process. Carbon dioxide from the atmosphere, and more importantly the soil mantle, is the essential agent that combines with meteoric water to produce the weak carbonic acid which then goes on to dissolve the limestone. The dissolution process is also reversible under certain conditions. When this occurs calcite is precipitated and cave formations result.

Passage Development

Caves are initially formed beneath the water table, where a fine network of joints and partings in the bedrock are exploited by moving subterranean water. Preferential use of a route by ground water may eventually create a cave sized conduit, the form and direction if which is dependant on weaknesses in the bedrock. Some cave passages occur where the limestone beds abut an impermeable rock, as is the case with Arctomys Cave, which is sandwiched between sandstones and shales. Ground water will also often exploit bedding plane weaknesses, as with Pinto Lake Cave, or flow along joints, as with Lizard Pot. Faults, through less important in dictating cave formation that joints or bedding plane weaknesses, will sometimes redirect the course of a cave passage for a short distance, Rat’s Nest Cave is believed to have formed along a low-angled thrust fault. (Yonge 1987).

If the limestone in which a cave formed is homogeneous, and thickly bedded, passage developed beneath the water table will take the form of a large pipe, solutional corrosion being equal on all surfaces. Such has been the case with The Subway in Castleguard Cave. More commonly, however, a joint or bedding plane causes differential enlargement to take place, creating an ellipse-shaped passage. A fine example of an elliptical tube lies just above the resurgence to Fryatt Creek Cave.

Cave passages formed above the water table develop in much the same manner as surface streams, with water down-cutting under the force of gravity. They tend to have a long and narrow canyon-like appearance. The First and Second Fissures in Castleguard Cave provide good examples of canyon passages. A drop in the water table will often produce a combination of these two basic passage shapes, giving a distinctive keyhole design. Good examples of keyhole passage can be found in many Rockies caves, notable examples being Mendips Cave and Rat’s Hole Cave at Crowsnest Pass. Caves formed exclusively beneath the water table, and having the characteristic round sections, are said to be phreatic, those formed above the water table, and having a narrow rift-like section are said to be vadose. Caves such as Yorkshire Pot and Castleguard contain passages of both types, the position of the cave relative to the water table having changed over time.

Cave Formations

Cave formations or 'speleothems' are the extraordinary shaped depositional features that caves are famous for. The process by which they are formed is the opposite from that which forms the caves themselves. As the carbon dioxide rich water percolates down through the limestone, it takes the calcium carbonate into solution. When it enters a cave where the carbon dioxide levels are similar to that of outside air, the carbon dioxide diffuses out of the water, and the calcium carbonate precipitates out onto the walls.

“Speleothems acquire their shape by five basic hydrologic mechanisms: dripping, flowing, seeping, pooled and condensation water (Hill and Forti, 1986). Stalagmites and stalactites are formed by dripping water where they are elongated in the vertical drip direction. Flowing water creates flowstone and rimstone dams. Coralloids grow from them films of seeping or splashing water. Helictites twist in all directions as water seeps from microscopic, internal canals. Calcite rafts form on the surface of pools whereas cave pearls and sparry calcites grow under water. Rims may be deposited on projections where condensation occurs. Added to the five basic hydrologic mechanism are other factors affecting speleothem shape; for example, bedrock porosity, bedding and evaporation.” (Yonge 1989)

The volume of speleothems in a cave depends on the amount of carbon dioxide lost by the waters which enter it, which in turn depends on the amount of organic activity in the soil above the cave. Thus caves in the tropics, with large amounts of organic debris and heavy precipitation, tend to contain more and larger speleothems than cold northern caves, such as those in the Rockies. In alpine karst, such as is prevalent in the Rockies, the source of ground water is often snow and ice-melt solutions, which becomes warm on entering caves. Contrary to intuition, ground water can carry increased levels of calcium carbonate as temperatures fall. Since almost all caves are formed in limestones and dolomite, carbonate minerals form the majority of speleothems. Calcite is by far the most common constituent of Rockies cave formations, although occasionally aragonite (a common cave mineral in the tropics), which has the same composition but a different crystal structure, (a polymorph), will compose formations.