Ape Cave, Lava tube system in Mount St. Helens National Volcanic Monument, Washington, US.
Ape Cave is a lava tube system beneath Mount St. Helens extending over 2 miles underground, with smooth rock walls sculpted by ancient lava flows. The temperature stays constant year-round at 42 degrees Fahrenheit throughout the passages.
The lava tunnel system formed roughly 2000 years ago when molten rock flowed down Mount St. Helens, leaving hollow passages as the lava drained away. Local people discovered it in the 1950s and began exploring these underground formations.
Local loggers discovered the cave in 1950, and a group of explorers called the Mount St. Helens Apes conducted initial investigations of the underground passages.
Wear sturdy footwear and bring multiple light sources to safely navigate the passages and explore both the easier upper and more challenging lower sections. Warm clothing is important since the underground air stays cool year-round.
The name comes from a group of explorers who called themselves the Mount St. Helens Apes during their early investigations of the passages. This naming from early visitors has stuck ever since.
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