Life on the Lava: How Craters of the Moon Went From Molten Rock to Pikas, Bats and Sagebrush

At first sight, Craters of the Moon in Idaho looks barren: 618 square miles of black rock, laid down by eruptions from the Great Rift, a 52-mile line of volcanic fissures, between 15,000 and 2,100 years ago. The flows are stacked on one another, a patchwork of different ages, types and textures. Yet plants and animals moved back in while the lava was still cooling, and today life fills nearly every niche. Rugged ground and scarce water kept out the roads, farms and power lines that cover much of the Snake River Plain, so the place remains largely untouched — though bighorn sheep and grizzly bears have been gone for almost 100 years.

Recent volcanic activity has created many different ecosystems. NPS photo.

On the lava

The lava comes in three textures: block lava, dense and angular; ʻaʻā, rough and jagged; and pāhoehoe, smooth, ropy or billowy — the most common here. Unlike warm, predictable Hawaiʻi, the Snake River Plain takes thousands of years to cover a lava flow in plants: a short growing season, gusty winds and hot summers — the black rock can reach 150°F or more.

• Lichens come first, growing at most 1–2 mm across a year, and color rocks and trees almost everywhere.
• Plants take root in cracks, where soil and water collect — more easily in fractured pāhoehoe than in ʻaʻā, which holds little water. Cracks in mounds called tumuli and in pressure ridges can be big enough for ferns. Over time plants break the rock down for others.
• Pikas, small relatives of rabbits, have a population here that shelters in piles of ʻaʻā and broken pāhoehoe and eats the plants around them, as do chipmunks, marmots and mice.

Only the most heat-tolerant plants can colonize the dark lava. NPS photo.

Under it: lava tubes

When the surface of a flow cooled while lava kept moving beneath it, it left tunnels — lava tubes — opened where their roofs later collapsed. Hundreds have been found, and thousands more are unexplored. Basalt insulates, so their temperature barely changes; some hold water or even ice all year — natural air conditioning and precious water in the high desert.

Lava tube beetles and mites spend their whole lives inside. The park has at least 11 species of bats, many hibernating in the tubes; ravens, pigeons and violet-green swallows nest near the entrances, and lizards, rodents, weasels and pikas use them too.

Lava tubes give shelter, and sometimes water, to the park's wildlife. NPS photo.

Sagebrush steppe

On older ground with better soil, windblown soil supports sagebrush steppe, the most common vegetation in the Intermountain West. Mountain big sagebrush dominates the north of the park, among grasses and five other sagebrush species; antelope bitterbrush and rubber rabbitbrush grow on the cinder cones. Sage-grouse, mule deer, pronghorn, songbirds and small mammals depend on it.

Sagebrush sparrows depend on sagebrush habitat. USFWS photo / Tom Koerner.

Kipukas: islands in the lava

A kipuka — a Hawaiian word — is a patch of older, vegetated ground surrounded by younger lava. More than 500 dot the park, from under an acre to tens of thousands of acres. On the Snake River Plain the cycle has repeated for millions of years: a shield volcano erupts, weathers, gathers soil and plants, and is then surrounded by newer flows until it is finally buried.

President John F. Kennedy added Carey Kipuka to the monument in 1962. Its intact sagebrush and grasses now serve as a model for restoring native vegetation in the monument and beyond; some kipukas hold some of Idaho's oldest junipers, and Carey and several others are protected as Research Natural Areas. President Clinton expanded the monument in 2000, citing the rarity and scientific value of kipukas among other reasons.

Carey Kipuka from the air. NPS photo.

Sources

Based on "Life Among the Lava Flows," National Park Service, Craters of the Moon National Monument and Preserve; a work of the United States government in the public domain.