A talus cave, also known as a boulder cave, is a type of

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

formed by the gaps between one, or more commonly many large boulders. Talus caves can be formed anywhere large boulders accumulate in a pile, such as in

scree Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. The term ''scree'' is ap ...

at the base of a cliff.

Formation

Talus caves are formed anywhere with a sufficient accumulation of large rocky material, and thus form in a wide variety of rock- in

New England New England is a region consisting of six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York (state), New York to the west and by the ...

, talus caves have been found in

anorthosite Anorthosite () is a phaneritic, intrusive rock, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic ...

schist Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...

slate Slate is a fine-grained, foliated, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade, regional metamorphism. It is the finest-grained foliated metamorphic ro ...

phyllite Phyllite ( ) is a type of foliation (geology), foliated metamorphic rock formed from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. I ...

, conglomerate,

marble Marble is a metamorphic rock consisting of carbonate minerals (most commonly calcite (CaCO3) or Dolomite (mineral), dolomite (CaMg(CO3)2) that have recrystallized under the influence of heat and pressure. It has a crystalline texture, and is ty ...

and

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

. Nevertheless, talus caves are more likely to form around outcrops of highly

competent Broad concept article: *Competence (polyseme), capacity or ability to perform effectively Competence or competency may also refer to: *Competence (human resources), ability of a person to do a job properly **Competence-based management, performa ...

rock, such as

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

gneiss Gneiss (pronounced ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under p ...

, which break cleanly along fractures. The exact mechanism of talus cave formation differs with geological context. Along at the bottom of cliff faces, talus caves are primarily created from the mass movement of rock due to

slope failure Slope stability refers to the condition of inclined soil or rock slopes to withstand or undergo movement; the opposite condition is called slope instability or slope failure. The stability condition of slopes is a subject of study and research i ...

, usually through

landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...

s creating

deposits which contain the caves. In steep-sided gorges, talus caves may form as a combination of slope failure and

downcutting Downcutting, also called erosional downcutting, downward erosion or vertical erosion, is a geological process by hydraulic action that deepens the channel of a stream or valley by removing material from the stream bed or the valley floor. The ...

by a stream or river, where smaller rocks and soil is washed away under large boulders, leaving a cave behind. In Scandinavia and other recently glaciated areas, many talus caves are the result of

neotectonic Neotectonics, a subdiscipline of tectonics, is the study of the motions and deformations of Earth's crust (geological and geomorphological processes) that are current or recent in geologic time. The term may also refer to the motions/deformations in ...

activity due to

post-glacial rebound Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound an ...

. These caves are found in fractured

roche moutonnée In glaciology, a roche moutonnée (or sheepback) is a rock formation created by the passing of a glacier. The passage of glacial ice over underlying bedrock often results in asymmetric erosional forms as a result of abrasion on the "stoss" (upstr ...

hills, where strong neotectonic earthquakes created large systems of fractures and caves. Several features on

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

have been found to resemble terrestrial

, giving rise to the possibility of extraterrestrial talus caves.

Characteristics

Talus caves are usually short, although the longest have up to several kilometers of explorable passages. Examples of long talus caves include in

Hälsingland Hälsingland (), sometimes referred to by the Latin name Helsingia, is a historical Provinces of Sweden, province or ''landskap'' in central Sweden. It borders Gästrikland, Dalarna, Härjedalen, Medelpad and the Gulf of Bothnia. It is part of ...

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

, with of passage, the Touchy Sword of Damocles cave in

New York New York most commonly refers to: * New York (state), a state in the northeastern United States * New York City, the most populous city in the United States, located in the state of New York New York may also refer to: Places United Kingdom * ...

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

with over of passage, and Merrills-Barn Door-And-The Hole-Scotts (MBDATHS) cave in

Vermont Vermont () is a U.S. state, state in the New England region of the Northeastern United States. It borders Massachusetts to the south, New Hampshire to the east, New York (state), New York to the west, and the Provinces and territories of Ca ...

, with of passage. Nevertheless, due to the complex, labyrinthine nature of larger talus caves the true length of many systems is unknown. Although talus caves are poorly studied compared to other types of caves, in areas not conducive to the formation of

solutional cave A solutional cave, solution cave, or karst cave is a cave usually formed in a soluble rock like limestone (Calcium carbonate, with chemical formula ''CaCO3''). It is the most frequently occurring type of cave. It can also form in other rocks, incl ...

s or

lava tube A lava tube, more rarely called a pyroduct, is a 'roofed conduit through which molten lava travels away from its vent'. If lava in the tube drains out, it will leave an empty cave. Lava tubes are common in low-viscosity volcanic systems. La ...

s they may be the most common type of cave. Some talus caves in the Northeastern United States are

ice cave An ice cave is any type of natural cave (most commonly lava tubes or limestone caves) that contains significant amounts of perennial (year-round) ice. At least a portion of the cave must have a temperature below 0 °C (32 °F) all ye ...

s, with perennial ice deposits inside the cave passages. Talus caves are important habitats for bats and

troglofauna Troglofauna are small cave-dwelling animals that have adapted to their dark surroundings. Troglofauna and stygofauna are the two types of subterranean fauna (based on life-history). Both are associated with subterranean environments – troglofa ...

, such as the

pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. Pseudoscorpions are generally beneficial to humans bec ...

'' Parobisium yosemite'' which is endemic to talus caves in

Yosemite National Park Yosemite National Park ( ) is a List of national parks of the United States, national park of the United States in California. It is bordered on the southeast by Sierra National Forest and on the northwest by Stanislaus National Forest. The p ...

. A few talus caves have been turned into

show cave A show cave—also called tourist cave, public cave, and, in the United States, commercial cave—is a cave which has been made accessible to the public for guided visits. Definition A show cave is a cave that has been made accessible to ...

s, such as the caves in the Lost River Reservation and Polar Caves Park in

New Hampshire New Hampshire ( ) is a U.S. state, state in the New England region of the Northeastern United States. It borders Massachusetts to the south, Vermont to the west, Maine and the Gulf of Maine to the east, and the Canadian province of Quebec t ...

, and the caves in

Pinnacles National Park Pinnacles National Park is a national park of the United States protecting a mountainous area located east of the Salinas Valley in Central California, about east of Soledad and southeast of San Jose. The park's namesakes are the eroded lef ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

References

{{Subterranea Cave geology Erosion landforms Caves by type