Cave and Mine Emergency Shelter

The Shelter Calculus

Caves provide genuine shelter advantages: stable temperature (caves maintain roughly the mean annual surface temperature of their region — about 50-55°F in most of the eastern US), complete wind protection, and protection from precipitation and direct radiation.

These advantages come with serious hazards that require specific knowledge to manage. The answer to "should I use this cave as shelter?" is not a simple yes or no — it depends on the specific cave, your ability to assess it, and whether better alternatives exist.

Cave Hazards

Air quality:

The most dangerous cave hazard, and the least visible. Carbon dioxide (CO₂) accumulates in cave low points (denser than air) and in dead-end passages with poor ventilation. Carbon monoxide can occur in some geological settings. Low oxygen can develop when CO₂ or other gases displace oxygen.

The danger: CO₂ at 10% concentration causes rapid incapacitation and unconsciousness before the person realizes anything is wrong. A cave that "feels stuffy" may already have dangerously elevated CO₂. A cave where candles or lighters won't stay lit has air quality that won't sustain a person either.

Signs of poor cave air:

• Candle or lighter difficulty staying lit
• Unusual stuffiness or still air smell
• Animals avoiding the area
• Headache, dizziness, or shortness of breath immediately upon entry

If any of these are present: exit immediately, moving toward outside air.

Structural stability:

Cave ceilings, walls, and floors are geological formations. Rock falls, undercut floors, and fragile speleothems (stalactites, stalagmites, other cave formations) exist in most wild caves. Moving through a cave in an emergency without a headlamp and careful movement risks fatal falls and rock displacement.

Flooding:

Caves often serve as drainage systems for surface water. A cave that's safe to enter during dry conditions can flood rapidly during a rainstorm with no warning to someone inside. This is called a flash flood risk in caves — far more dangerous than surface flash floods because there's nowhere to go. Never shelter in a cave during periods of rain or approaching rainstorms without verified knowledge that the specific cave section doesn't flood.

Vertical drops:

Cave systems often include vertical drops — pits, shafts, and holes — that are invisible in darkness. Entering a cave without adequate lighting risks walking into a vertical drop.

What Makes a Cave Acceptable as Shelter

A cave appropriate for emergency shelter has:

1. Good air quality confirmed: Airflow felt at the entrance, no stuffiness, fire sources (lighter, candle) operate normally inside
2. Known flood risk: You know this cave system and know the entry section doesn't flood — or you have clear visual evidence that the section you're in is above any drainage path
3. Adequate ceiling and floor stability: The specific section you're using has stable rock overhead, no obvious undercut floors
4. Known depth: You're in a section of the cave you can fully see or have explored previously — not proceeding into unknown depths without lighting and navigation
5. Known location to external parties: Someone outside knows where you are and when to expect you

If you don't know a cave well, the appropriate approach is to use only the entrance area — the portion with natural light and natural airflow — for shelter from wind and precipitation, while remaining ready to exit quickly.

Abandoned Mines: Stay Out

The Forest Service, BLM, and CDC are unequivocal: abandoned mines are not shelters. They are some of the most hazardous structures in the American backcountry.

The specific hazards:

Oxygen-deficient atmospheres: Rock oxidation and biological processes consume oxygen in confined mine spaces. Deaths occur at abandoned mines regularly — often in clusters, where a first victim is overcome and rescuers without breathing apparatus follow them in.

Structural instability: Mine timbering fails over time. The "hang time" for unsupported mine ceilings is unpredictable. A mine that's stood for 50 years may collapse without warning. Vertical shafts — often hidden at the floor level and sometimes covered with rotting timber — drop 50-200 feet.

Chemical contamination: Mine tailings and processing areas often contain arsenic, lead, mercury, and other heavy metals at concentrations dangerous to touch or inhale. Acidic mine drainage is corrosive.

The appearance of stability is not reliable. Many mine deaths involve entrances and near-entrance areas that looked structurally sound.

If you find an abandoned mine in the wilderness: keep your distance. Do not enter under any circumstances, regardless of the emergency.

Lava Tubes (Hawaii and Pacific Northwest)

Lava tubes — tunnels formed by flowing lava cooling on the surface while the interior continues to flow — are a specific cave type relevant to Hawaii and the volcanic areas of Oregon and Washington.

Lava tubes have different hazard profiles than limestone caves: they're generally structurally more stable in the interior, have simpler geometry, and don't have the same chemical air quality issues as some mine environments. However:

• Sharp lava rock edges (aa and basalt edges are razored) cause severe cuts in darkness
• Uneven, loose lava rock floor creates fall risk
• Some lava tubes have sections that are structurally compromised
• Air quality should still be checked before extended use

Known, locally recognized lava tubes (like those at Ape Cave, Washington, or Thurston Lava Tube, Hawaii) have assessed stability and are reasonably safe. Unknown or unassessed tubes: apply the same caution as any cave.

The Practical Shelter Decision Tree

If you're in a wilderness emergency and considering cave shelter:

1. Do you have adequate lighting (headlamp with fresh batteries)?
2. Is there visible airflow (not dead air)?
3. Does a lighter or candle burn normally inside the entrance?
4. Is this the entrance/known section only, not unknown depths?
5. Is there no evidence of flood risk from recent water staining above head height in the cave?
6. Have you checked for overhead instability before committing to a location?

If yes to all: the cave entrance section is a reasonable shelter option for wind and precipitation protection.

If any answer is no: use surface alternatives (tarp, bivy, natural windbreaks) rather than taking uncertain underground shelter.

Caves are useful wilderness shelter when properly assessed. They're not the default go-to just because they exist. The shelter option that's known and assessed is always better than the option that looks convenient.