Caves have enthralled humanity across cultures for thousands of years. These mystical portals to the underworld inspire awe with their darkness and surprising geological wonders. Over time, patterns have emerged in the diverse shapes, sizes, locations and formats of caves worldwide. This guide provides an in-depth look at how the many different types of caves are formed and their key features.
The Cave Formation Process
Caves take shape through various geological processes spanning millions of years. The solubility of rock, presence of fractures, seismic shifts, volcanic activity, erosion and melting ice all contribute to cave origins.
Soluble rocks like limestone, dolomite and gypsum slowly dissolve from carbonic acid in groundwater. This carves out cave passages, sinkholes and karst landscapes over eons. Weak acid rain also enlarges fissures into caves over time.
Caves also form through tectonic shifts causing cracks and fractures in rock, which water erosion then enlarges. Volcanic lava tubes arise when the tops of lava flows harden while inner lava keeps flowing, then drains away.
Powerful ocean waves crash into and scour out sea caves along coastlines worldwide. Glaciers carve winding tunnels in ice and bedrock through melting ice, internal heat and pressure of their slow flows.
Categorizing Caves by Their Structure and Features
While each cave is unique, they can be grouped into types sharing common structural designs and decorative formations that reveal clues about their creation.
Abundant along rocky shores and cliffs, sea caves are carved by eroding ocean waves. The swirling force of the water sculpts curved walls, arched ceilings, tunnels extending into cliffs, and caverns of various sizes with undulating floors and boulders. Sea caves often contain pools of vivid blue or green seawater within their chambers at depths reachable by divers and snorkelers.
Famous Examples: Sea caves along the Great Ocean Road in Australia, Fingal’s Cave in Staffa, Scotland formed from fractured hexagonal basalt columns, the Blue Grotto sea cave illuminated by brilliant blue light in Capri, Italy.
Lava Tube Caves
When the tops and sides of flowing basaltic lava cool and harden into a crust, insulated molten lava keeps streaming in a channel beneath it. Once drained, these natural tubes are left as winding, smooth-floored caves called lava tubes. They range from narrow crawlways to expansive tunnels large enough to walk through, extending for miles underground near volcanoes. Distinctive lava drips, stringy lava “rootlets” and lava stalactites decorate their interiors.
Famous Examples: Kazumura Cave and Thurston Lava Tube in Hawaii reaching over 40 miles long, the 25 mile long Cueva del Viento system in Tenerife, Canary Islands, Lava Beds National Monument lava tubes in California.
Limestone caves, also known as karst caves, are by far the most abundant in the world due to the widespread presence of soluble limestone and dolomite rock types. Seeping rainwater infused with carbon dioxide slowly erodes passageways, chambers and sinkholes into these rocks over tens of thousands of years. Limestone caves exhibit grand, cathedral-like chambers with dramatic stalactite and stalagmite formations, columns, soda straws, cave pearls, limestone curtains, rimstone dams and transparent cave pools. Extensive networks can span hundreds of miles.
Famous Examples: The mammoth Mammoth Cave system in Kentucky with over 405 miles mapped, Škocjan Caves and Postojna Cave in Slovenia, one of the largest systems in Europe, the extensive Waitomo Cave network full of glowworms in New Zealand.
Meltwater and geothermal heat bores winding tunnels up to 1,000 feet deep inside glaciers, lined with glistening cathedral-like ice walls sculpted by the flowing ice. Moulin potholes form vertical glacier caves. When glaciers recede, ice caves and chasms within them open access to the bedrock beneath. Colorful mineral debris stripes the icy walls. Extreme cold, danger of collapse, and sudden flooding make glacier caves among the most treacherous.
Famous Examples: Paradise Ice Caves within the Paradise Glacier on Mt. Rainier in Washington state, USA; Eisriesenwelt Werfen Ice Cave near Salzburg, Austria stretching over 40 miles long; Kungur Ice Cave in the Ural Mountains of Russia.
Lava Blister Caves
During lava flows, the outer layer can bulge into a dome shape and then drain out, leaving behind a hollow blister cave. These range from small bubble-like spheres to expansive rooms, some with fascinating lavacicles on the ceiling. Unlike lava tubes, they do not have openings at both ends. Blister caves are found in Hawaii, Canary Islands, Australia and other volcanic locations.
Famous Examples: Keokeo Lava Tube, Kapoho Blowhole and Kazumura Caves in Hawaii; Ulgas de Cabrito blister cave in Lanzarote, Canary Islands.
Erosional caves are carved out by the action of wind, water, ice, gravity and acids slowly dissolving or abrading rock over eons. Describing the majority of non-lava, non-glacial caves, this category encompasses solutional cave systems in limestone, tunnels carved through sandstone, tears and shafts in granite, and sea worn caverns. Erosion caves vary greatly in size and shape.
Famous Examples: Antelope Canyon, a narrow, curvy slot canyon eroded in sandstone in Arizona, USA; Reed Flute Cave, a limestone cave in Guilin, China filled with unique calcite formations.
Shifts in the earth’s crust cause fractures, fissures and joints to form in bedrock. Over time, flowing water or seeping acids penetrate these cracks, exploiting the zones of weakness and enlarging them into caves. They are very common in limestone terrains subject to tectonic stresses. Tectonic caves tend to have straight, vertical sections rather than sinuous shapes.
Famous Examples: Minas Gerais caves in Brazil formed in limestone cliffs, with extensive underground lakes and unique speleothems; the giant Crystal Cave filled with massive selenite crystals in California’s Sequoia National Park resulting from seismic activity.
Talus caves or rock shelters form small, shallow spaces among unstable piled up boulders and rock debris found at the base of cliffs and moderately angled slopes known as talus slopes. The jumbled rocks create pockets, tunnels and crevices perfect for shelter for climbers, wildlife and prehistoric humans. They are numerous but often unnamed and unmapped.
Famous Examples: Various small talus caves in the boulder fields below glaciers and mountain peaks; ancient humans used talus caves like Kebara Cave in Israel.
While less common than limestone caves, erosion can carve out significant caverns and tunnels in porous, iron-cemented sandstone. These caves exhibit grand rooms, undulating floors, fascinating striped patterns, ancient fossils and petrified wood embedded in the walls. They contain rare speleothem types not found in limestone caves.
Famous Examples: Majesty Cave, the largest sandstone cave open to the public in the U.S., in Colorado; eerie hollows carved under the Tsingy de Bemaraha limestone plateau in Madagascar; the red striped marble caverns of Üçağız Cave in Turkey.
Solid granite bedrock seems unlikely to host caves, but erosion over time can penetrate fractures and joints in granite to sculpt tunnels, unusual patterns and chambers very different from limestone caves. Water percolating through the rock also creates beautiful crystalline speleothems. Granite boulders piled up on talus slopes create shelter caves as well.
Famous Examples: Modipe Cave featuring rare calcium carbonate crystals in South Africa’s Kalahari Desert; Eagle Cave in Colorado with hexagonal feldspar crystal formations.
Caves can form within the calcium carbonate skeletons of living coral structures as the coral grows and branches out. Coral caves contain tunnels winding through the reef, openings to the sea, and caverns with coral walls and seawater pools. Most occur below shallow sea level, although uplifted fossil coral caves exist.
Famous Examples: The intricate coral cave systems of the Marieta Islands off Puerto Vallarta, Mexico; The Great Blue Hole, a circular underwater sinkhole cave in the Light House Reef of Belize.
Cave Exploring Gear and Conservation Tips
- Cave exploring requires proper equipment for lighting, safety, navigation and conservation:
- Each caver needs 3 light sources – main helmet lamp plus backups. LED systems last the longest.
- Sturdy boots with grip prevent slips and provide ankle support. Knee pads help crawl through small spaces.
- Safety gear: climbing harnesses, ropes, ascending gear for pit caves and vertical passages.
- Neoprene wet suits or dry suits with warming layers for cold caves.
- Helmets protect from falling debris. Gloves avoid mineral oil and particle transfer to formations.
- Caving requires leaving no trace and no unsecured artifacts:
- Take nothing but photographs. Never touch, break or remove cave formations or contents.
- Travel carefully to avoid kicking up excess dust or sediments that can damage cave features. Stay on marked trails when present.
- Never leave litter, food, equipment or other artifacts behind. Everything brought in must be carried out.
- Report vandalism or unauthorized activity to cave managers. Follow all access rules and obtain permits when required.
Our planet contains an abundance of awe-inspiring caves that give us a window into the continual geological processes shaping the earth. Created over millions of years by volcanic activity, tectonic shifts, erosion in various forms and melting glaciers, caves reflect incredible diversity based on how they formed. Even caves carved in solid rock can contain remarkably ornate secondary mineral deposits and crystal formations on their ceilings, floors and walls. As exquisite natural wonders containing clues to both the planet’s distant past and valuable resources for the future, caves deserve both our admiration and thoughtful protection. Those who explore caves carry the privilege and responsibility of preserving their magic for all humanity.