Maine's Enchanted Cave

Introduction

Maine caves are generally categorized as sea caves, talus/fissure caves, and solution caves. Sea caves form along zones of weakness in the rock which may include areas of cracks or where there are differences in abrasive resistance. Since the action of waves is concentrated at the base of cliffs, an overhang forms (Figure 1). The Ovens of Mount Desert Island are examples of Maine sea caves. Talus or fissure caves are typically found in various types of granite and are caused by large slabs of rock and boulders which have shifted as a result of slides and collapses (Figure 2). An example of a Maine talus cave includes the Allagash Ice Cave which is noted for being the longest of its type in New England. Solution caves in Maine are formed in carbonate rocks, such as limestone and marble, by the action of moving water. Water seeps through soil and fractures in the underlying bedrock where it eventually reaches the water table. As the water table naturally lowers, carbonic acid contained in the water dissolves minerals such as calcite, the major constituent in limestone. This process in turn forms tunnels, irregular passages, and large solution caverns (Figure 3). Solution caves are perhaps the best known of these cave types and are made famous by such sites as Mammoth Caves in Kentucky, Carlsbad Caverns in New Mexico, and the Luray Caverns of Virginia. The Enchanted Cave of northwestern Maine is also classified as a solution cave and is the subject of this webpage.

Figure 1

Figure 2

Figure 3

Maine's Cave Protection Act

Maine caves are protected by law, according to the Maine Cave Protection Act, which grants specific landowner rights as well as prohibiting activities which detract from the natural, historical, and archaeological value of caves.

Enchanted Cave

Enchanted Cave is in a small band of limestone rock in northwestern Maine, within the Devonian Tarratine Formation. Solution caves such as this are not common in Maine and are known to occur in only three localities. Areas where conditions support the formation of such caves typically exhibit absent or reduced surface water drainage and a rocky, barren landscape and are referred to as having a karst landscape.

The processes involved in the creation of Enchanted Cave, as well as other similar limestone solution caves, involve rain which picks up carbon dioxide as it falls through the atmosphere. As this precipitation percolates through the soil, more carbon dioxide from plant roots and decaying vegetative matter becomes dissolved in the water to form a weak acid, carbonic acid, as well as complex organic acids called humic acids. This ground water can readily dissolve limestone, creating erosional features in the rock. As water levels are lowered to leave open fissures and caves, dissolved calcium carbonate may precipitate to form beautiful dripstone features known as speleothems. These depositional features form above the water table.

The simplified chemical reactions involved include:

The formation of a weak acid
H₂0	+	CO₂	→	H₂CO₃
water (liquid)	+	carbon dioxide (gas)	forms	carbonic acid (dissolved in water)

The dissolution of limestone
CaCO₃	+	H₂CO₃	↔	Ca²⁺	+	2(HCO₃)^-
calcium carbonate (solid)	+	carbonic acid (dissolved in water)	react to form	calcium ions (dissolved)	and	bicarbonate ions (dissolved)

The precipitation of calcite
Ca²⁺	+	2(HCO₃)^-	↔	CaCO₃	+	CO₂	+	H₂O
calcium ions (dissolved)	and	bicarbonate ions (dissolved)	react to form	calcium carbonate (solid)	and	carbon dioxide (gas)	and	water (liquid)

Virtual Tour of Enchanted Cave

Two of the most common speleothems include stalactites and stalagmites. Stalactites hang downward from the ceiling and are formed as drop after drop of water with dissolved calcium and bicarbonate ions slowly trickles through cracks in the cave roof. As carbon dioxide is released to the atmosphere and water evaporated, a residue of calcium carbonate is deposited. Stalagmites grow upward from the floor of the cave generally as a result of water dripping from overhanging stalactites. Although stalagmites have not been observed in the 140 meter expanse of Enchanted Cave, the following gallery of photographs should provide a glimpse into this very "enchanted" place.

*Entrances to Enchanted Cave*
Figure 4	Figure 5

*Erosional Features Due to Dissolution of Rock*
Figure 6	Figure 7	Figure 8	Figure 9

*Depositional Features*
Figure 10	Figure 11	Figure 12

Fossils

Figure 13

Additional Information

Information on caves, caving, and safety issues:

U. S. Geological Survey - use search engine to find information and teacher packets
National Speleological Society
Boston Grotto
Maine Caves

Solution cave formation:

Exploring Earth ES1405: Observe an animation of cave formation
Encarta Formation of Limestone Caves

Information on limestone solution caves and the science of their formation:

National Caves Association

Photographs provided by William D. O'Brien and Jason G. Choquette.

Web site by Daniel B. Locke

Originally published on the web as the February 2007 Site of the Month.

Last updated on January 10, 2008