Craters of the Moon National Monument and Preserve is a vast volcanic landscape in south-central Idaho that covers roughly 1,600 square kilometers of basaltic lava flows, cinder cones, and fissures along a feature known as the Great Rift. Despite the name, it has nothing to do with the actual Moon. The landscape earned its title because early visitors thought its stark, dark terrain resembled a lunar surface, and the name stuck when the area was designated a national monument in 1924. What makes the site remarkable is the combination of its geological youth, its eruptive complexity, and the surprising amount of life that has found ways to thrive in what looks, at first glance, like one of the most inhospitable places on Earth.
The Great Rift and How the Lava Field Formed
The volcanic activity at Craters of the Moon is tied to a deep fracture system called the Great Rift, a set of fissures running roughly north-south across the Snake River Plain in Idaho. This is not a single volcano with a summit crater. Instead, magma reached the surface through a series of cracks in the earth’s crust, building up an enormous field of overlapping lava flows and volcanic cones over thousands of years. The Craters of the Moon lava field is a composite of more than 60 individual lava flows, 25 cinder cones, and at least eight distinct eruptive fissure systems.1GSA Bulletin. Contrasting magma types and steady-state, volume-predictable, basaltic volcanism along the Great Rift, Idaho That makes it one of the best-preserved basaltic volcanic landscapes in the continental United States.
The Snake River Plain itself sits above a track of ancient hotspot volcanism, the same deep heat source now beneath Yellowstone. As the North American plate drifted southwest over this hotspot over millions of years, it left behind a trail of volcanic activity. The Great Rift taps into residual heat and magma reservoirs in the crust, and the resulting eruptions have been basaltic rather than the explosive, silica-rich eruptions more typical of Yellowstone itself. The basalt here is iron-rich and relatively fluid when molten, which is why the lava traveled so far from its source vents and spread into broad, thin sheets rather than building towering stratovolcanoes.
Eight Eruptive Periods Spanning 15,000 Years
The volcanic history of Craters of the Moon is not a single eruption but a repeating cycle. Field mapping, radiocarbon dating, and paleomagnetic studies have identified eight separate eruptive periods stretching back roughly 15,000 years. Each period lasted several hundred years or less and was separated from the next by quiet intervals ranging from a few hundred to several thousand years.2GSA Bulletin. Contrasting magma types and steady-state, volume-predictable, basaltic volcanism along the Great Rift, Idaho The most recent eruptive period ended around 2,100 years ago, which in geological terms is practically yesterday.
During that final known eruptive period, lava flows were erupted between about 2,500 and 2,000 years ago along the Great Rift.3Journal of Petrology. Petrological and Mineralogical Variations in 2500–2000 yr B.P. Lava Flows, Craters of the Moon Lava Field, Idaho These youngest flows are the ones visitors encounter most directly along the monument’s loop road. They are strikingly dark and rough, their surfaces barely touched by weathering. Some are so fresh-looking that early geologists assumed they were only a few centuries old before radiometric dating confirmed their true age.
The lava field as a whole contains roughly 30 cubic kilometers of lava and associated volcanic debris.4GSA Bulletin. Contrasting magma types and steady-state, volume-predictable, basaltic volcanism along the Great Rift, Idaho That is an enormous volume spread across a landscape about the size of a mid-sized city, layer upon layer of flows stacked and interleaved with cinder deposits from the 25 cones.
What the Landscape Looks Like Up Close
Two main types of basaltic lava dominate Craters of the Moon. Pahoehoe lava has a smooth, ropy surface created when relatively fluid lava flows cool slowly enough for the crust to wrinkle and fold. Aa lava, by contrast, is jagged, rough, and clinker-covered, the result of lava that lost gas and cooled more quickly as it moved. Both types are abundant in the monument, sometimes side by side from the same eruption, depending on how the lava cooled as it traveled away from the vent.
The cinder cones are another defining feature. These steep-sided, symmetrical hills formed when gas-charged lava was thrown into the air from a vent, cooled into fragments mid-flight, and piled up around the opening. Some of the cinder cones at Craters of the Moon are textbook examples of the form, used in geology courses to illustrate the type. Inferno Cone, for instance, offers a short but steep climb to a summit with panoramic views across the lava field, and the symmetry of its shape is nearly perfect.
Below the surface, an extensive network of lava tubes threads through the flows. These tubes formed when the outer surface of a lava flow solidified while molten lava continued to drain through the interior, leaving behind hollow tunnels. Some are large enough to walk through. Indian Tunnel, one of the most accessible, is over 240 meters long with sections where the ceiling has collapsed, letting light stream in. Others remain fully enclosed and extend deep underground into permanent darkness.
A Stand-In for Mars
Craters of the Moon has attracted attention from planetary scientists because its basaltic lava tubes and flow surfaces bear a strong resemblance to volcanic features on Mars. Researchers studying what Martian caves might look like, and what kinds of life could survive in them, have used Craters of the Moon as a terrestrial analog. The basalt composition at the monument is especially useful for this work because it shares chemical traits with rocks analyzed on the Martian surface.5Journal of Geophysical Research: Planets. Life Underground: Investigating Microbial Communities and Their Biomarkers in Mars‐Analog Lava Tubes at Craters of the Moon National Monument and Preserve
A detailed chemical comparison found that several Craters of the Moon basalt flows share notable similarities with specific Martian rock classes. Some of the older flows, like the Kimama flow dated to more than 18,000 years ago, have high iron, titanium, and phosphorus contents that resemble the Wishstone and Watchtower class rocks analyzed by NASA’s Spirit rover at Gusev Crater on Mars. The youngest flows, including the Blue Dragon flow from about 2,050 years ago, share silica and alkali characteristics with clasts found in a Martian meteorite recovered on Earth.6American Mineralogist. Craters of the Moon National Monument basalts as unshocked compositional and weathering analogs for martian rocks and meteorites These overlaps across flows of different ages suggest the site can shed light on a range of igneous processes that may have occurred on Mars.
The astrobiology angle goes beyond rock chemistry. Inside the lava tubes, researchers have found that secondary mineral deposits on cave walls support diverse and active microbial communities. These microbes rely primarily on breaking down organic matter, with some capable of using chemical energy from the rock itself to drive key nutrient cycles.7Journal of Geophysical Research: Planets. Life Underground: Investigating Microbial Communities and Their Biomarkers in Mars‐Analog Lava Tubes at Craters of the Moon National Monument and Preserve The practical question this research tries to answer is whether instruments on current or future Mars missions could detect similar biosignatures if microbial life ever existed in Martian lava tubes.
How Soil Builds from Nothing
One of the more interesting scientific stories at Craters of the Moon has to do with how soil develops on young lava. Bare basalt is not exactly inviting to plants, but given enough time, organic material accumulates in cracks and depressions on the lava surface. On the younger flows, these pockets of organic soil are the dominant soil type, building up from biological debris rather than from the breakdown of the rock itself. Plants adapted to harsh, nutrient-poor conditions colonize crevices, and when they drop leaves, needles, or die back, the organic matter collects and slowly forms thin soils classified as Folists.8Soil Science Society of America Journal. Organic Soils on Basaltic Lava Flows in a Cool, Arid Environment
The pace of this process depends heavily on the age of the flow. Research across flows ranging from about 2,100 to 18,400 years old found two distinct patterns. On flows younger than about 13,000 years, the shallow organic soils cover up to roughly a quarter of the surface at most, clinging to crevices while most of the rock remains bare. On flows older than about 13,900 years, deeper mineral soils begin to take over, and by the time a flow reaches 18,400 years old, soil coverage exceeds 95 percent.9Soil Science Society of America Journal. Episodic Soil Succession on Basaltic Lava Fields in a Cool, Dry Environment Visitors walking across the youngest flows in the monument are literally watching the earliest stages of a process that will take thousands more years to complete.
This also means the monument is a natural laboratory for studying soil formation from scratch. The flows are well-dated, they sit in the same climate, and they span a wide age range. Few places on Earth offer such a clean chronosequence for understanding how bare rock becomes productive land.
Pikas in the Lava
American pikas are small, round-eared relatives of rabbits that most people associate with high mountain talus fields. They are famously sensitive to heat and are often cited as an early indicator species for the effects of climate change on mountain ecosystems. So it surprised biologists to find a thriving population of pikas living at Craters of the Moon, which sits at a relatively low elevation and gets extremely hot in summer, with surface temperatures on the dark basalt regularly soaring well above what pikas can tolerate for any extended period.
The trick is the lava itself. The jumbled, broken rock of the basalt flows functions like natural air conditioning. Cool air pools in the gaps and tubes beneath the surface, creating a dramatic temperature difference between the exposed rock and the crevices just below. Pikas at Craters of the Moon have adapted their daily routines around this. Compared to pikas living in traditional alpine talus habitat, the Craters of the Moon pikas are less active aboveground throughout the day, especially at midday when surface temperatures peak and the insulating effect of the underground spaces is most pronounced.10Western North American Naturalist. Activity Patterns and Foraging Behavior of American Pikas (Ochotona princeps) Differ between Craters of the Moon and Alpine Talus in Idaho They shift to a strongly dawn-and-dusk activity pattern and spend less time gathering hay and displaying territorial behavior, though they still manage to fill a similar number of food caches as their alpine counterparts.
This population has caught the attention of conservation biologists because it complicates the narrative that pikas are uniformly doomed by warming temperatures. A review of pika conservation status noted that several low-elevation, warm sites, including Craters of the Moon, retain active pika populations, demonstrating the adaptive capacity of the species when suitable rock habitat with cool subsurface microclimate is available.11Journal of Mammalogy. Conservation status of American pikas (Ochotona princeps) The pikas cope by retreating into the cool interstices of their lava habitat and supplementing restricted daytime foraging with nocturnal activity. It is a reminder that habitat structure, not just latitude or elevation, plays a critical role in determining where a species can persist.
Invasive Plants and the Edges of the Lava
The interior of the lava field is harsh enough that relatively few invasive species have gained a foothold, but the margins of the monument tell a different story. Where the lava gives way to sagebrush steppe and where roads and agricultural land border the preserve, invasive annual grasses and weeds have made significant inroads. Cheatgrass, tumblemustard, and related invasive annuals are most abundant at lower elevations and close to roads or agricultural fields at Craters of the Moon.12Soil Science Society of America Journal. Differential Species Responses to Aspects of Resistance to Invasion in Two Columbia Plateau − Protected Areas Higher elevation and greater distance from disturbed areas were the strongest factors keeping these invaders out of the native plant communities.
Cheatgrass is a particular problem across the intermountain West because it cures out into dry, flammable fuel earlier in the season than native grasses, increasing fire frequency. In the sagebrush communities surrounding the lava field, more frequent fire favors cheatgrass over native perennials, creating a feedback loop that progressively degrades the habitat. The lava itself acts as a natural firebreak in many places, and the crevice-dwelling plants on the youngest flows are largely insulated from this cycle. But the buffer zones and kipukas, those older islands of soil and vegetation surrounded by younger lava, are more vulnerable. These kipukas are biologically rich patches that serve as refuges for native plants and animals, and their loss to invasive grass encroachment would ripple through the monument’s ecology.
The Petrology Behind the Scenery
Not all of the lava at Craters of the Moon is chemically identical. The eruptions produced a range of basalt compositions, from relatively primitive olivine-rich flows to more chemically evolved types. Analysis of the youngest flows, those erupted between 2,500 and 2,000 years ago, found that the lavas contain iron-rich olivine, rare iron-rich pyroxene, and minor alkali feldspar. The chemical diversity within this single eruptive period can be explained largely by crystal fractionation and accumulation, with an overlay of contamination from rhyolitic material in the surrounding crust.13Journal of Petrology. Petrological and Mineralogical Variations in 2500–2000 yr B.P. Lava Flows, Craters of the Moon Lava Field, Idaho
What this means in plain terms is that the magma chamber beneath the Great Rift was not a single well-mixed pot. As minerals crystallized and settled, the remaining liquid changed composition. Sometimes the rising magma also incorporated bits of the silica-rich rock it passed through on the way to the surface. The result is a lava field that looks uniform to the casual eye but contains real compositional variety when you examine it closely. That variation is part of what makes the site valuable to researchers studying how basaltic magma systems evolve, both on Earth and on other planets.
When Will It Erupt Again
Craters of the Moon is not extinct. The recurrence interval between eruptive periods along the Great Rift ranges from several hundred to about 3,000 years. The current quiet interval has lasted approximately 2,100 years, which puts it squarely within the historical range for a pause between eruptive periods. Geologists have concluded that another eruptive period seems likely within the next 1,000 years, and the volume-predictable pattern of past eruptions suggests that when it does happen, roughly five to six cubic kilometers of lava could be produced.14GSA Bulletin. Contrasting magma types and steady-state, volume-predictable, basaltic volcanism along the Great Rift, Idaho
That is not an immediate emergency. A thousand-year window is long by any human planning horizon, and basaltic fissure eruptions, while dramatic, tend to be far less explosive and destructive than the eruptions people fear from places like Yellowstone or Mount St. Helens. The lava would flow, probably slowly enough for evacuation of the sparsely populated surrounding area. But it would reshape the landscape all over again, burying some of the current lava flows under new ones and resetting the ecological clock on whatever ground it covers.
The U.S. Geological Survey monitors the area and considers the Great Rift an active volcanic zone. Seismic monitoring and deformation studies would likely provide warning well before any eruption began, as magma moving through the crust creates detectable signals. For now, the monument sits in its quiet phase, slowly accumulating soil, growing its crevice forests, and hosting pikas that have figured out how to live on a landscape that, geologically speaking, is still warm from its last round of activity.
NASA’s Training Ground
Craters of the Moon has a long history as a training site for space exploration. In the late 1960s and early 1970s, NASA sent Apollo astronauts to the monument to practice geological fieldwork before their lunar missions. The reasoning was practical: the lava field’s rugged, barren terrain offered a reasonable approximation of what the astronauts would encounter on the Moon, and the volcanic features gave them hands-on experience identifying rock types and geological structures in an unfamiliar landscape. Alan Shepard, Edgar Mitchell, Joe Engle, and Eugene Cernan were among the astronauts who trained there.
That connection to space exploration has persisted. The astrobiology research in the monument’s lava tubes, the chemical comparisons between its basalt and Martian rocks, and the ongoing studies of microbial life in extreme environments all tie back to the same quality that drew NASA in the first place: Craters of the Moon is one of the closest things on Earth to an alien landscape. It is also far more accessible than most volcanic sites of comparable scale, sitting alongside a paved highway in Idaho with a visitor center and maintained trails. That combination of scientific value and physical accessibility is rare, which is why the site keeps drawing researchers from fields as varied as volcanology, soil science, astrobiology, and wildlife ecology, all working on different questions but sharing the same strange, dark ground.