A mountain of solid stone that will not stay still.

Devils Tower, the striking rock formation rising above northeastern Wyoming, appears immovable from the ground. Its vertical columns, sheer walls and broad summit have made it one of the most recognizable natural landmarks in the United States. Yet sensitive scientific instruments have shown that the tower is not perfectly still.

Measurements collected at the summit indicate that Devils Tower makes extremely small, nearly continuous movements. The motion is not visible to visitors and does not mean the formation is about to collapse. Instead, it reflects a familiar principle of structural and earth science: even large natural rock masses respond to wind, temperature, gravity and faint vibrations traveling through the ground.

The findings offer a closer look at how an iconic geologic feature behaves as a whole. They also add useful information for scientists studying fractured rock, erosion and the long-term stability of prominent landforms.

Seismometers Measure Subtle Motion at Devils Tower

A research team placed a seismometer on the summit of Devils Tower under a National Park Service permit and recorded its motion over roughly 21 hours. Additional instruments were positioned near the base to help distinguish movement within the tower from vibrations arriving through the surrounding ground.

Seismometers are best known for detecting earthquakes, but they can also record much smaller environmental vibrations. Wind passing around a tall rock formation, distant seismic activity, weather-related changes and human activity can all produce signals that modern instruments can detect. In this case, the sensors documented a subtle oscillation associated primarily with wind.

The most prominent measured frequency was close to 1.1 hertz, meaning the tower’s natural motion repeated a little more than once per second. That description can sound dramatic, but the amplitude of the movement was extremely small: on the order of micrometres, or millionths of a metre. Such movement is far below the threshold of human sight and does not cause the summit to visibly sway.

On quieter days, the rock formation can still register very low-level motion from ambient seismic noise. This background vibration is generated by many natural sources, including ocean waves, weather systems and distant ground motion. The ability to detect it demonstrates the sensitivity of the instruments rather than an immediate concern about the tower’s condition.

Scientists often study the natural frequencies of structures and rock masses because those frequencies reveal how an object responds to external forces. Buildings, bridges, trees, cliffs and rock towers all have characteristic modes of vibration. Understanding those patterns can help researchers separate normal behavior from unusual changes that may deserve closer monitoring.

Why a Huge Rock Formation Can Flex

Devils Tower rises about 867 feet, or 265 metres, above the Belle Fourche River valley. Its size may suggest complete rigidity, but no real material is perfectly rigid. When wind applies force to a tall formation, the rock can deform by a minuscule amount and then return to its original position. This is an elastic response, not evidence that the tower is bending in a way that visitors could observe.

The measurements identified two closely spaced principal modes, near 1.1 and 1.2 hertz. These motions appear to correspond broadly to movement in different horizontal directions, such as east-west and north-south. Researchers also detected a weaker twisting component around the tower’s vertical axis.

These patterns matter because Devils Tower is not a single flawless block of stone. Its famous fluted appearance comes from large polygonal columns separated by joints. The columns formed as molten rock cooled and contracted underground millions of years ago. Over time, erosion removed surrounding rock and sediment, exposing the resistant igneous body seen today.

The precise geologic setting and formation history of Devils Tower have been discussed by geologists for generations. The National Park Service describes it as an igneous intrusion exposed by erosion, while scientific discussions have considered several possible forms of intrusion. What is clear is that cooling produced the prominent columns that now define the landmark.

Joints between those columns are an important part of the tower’s behavior. They influence how water enters the rock, how freeze-thaw cycles affect surfaces, how individual pieces weather and how vibrations move through the formation. A tower made of jointed columns can behave differently from a small, intact laboratory sample cut from the same type of rock.

What “Softer Than Rock” Means in This Research

One notable interpretation from the seismic measurements is that Devils Tower appears to have a lower effective stiffness than intact rock samples tested in laboratory conditions. Reports about the work have described the formation as behaving roughly seven times “softer” than an equivalent piece of unfractured rock.

In this context, softer does not mean that the tower is soft to the touch or weak in an everyday sense. It refers to the way the entire rock mass responds to force. A jointed formation may flex slightly more because narrow gaps, fractures and contacts between columns allow very small relative movements. This is a common issue in rock mechanics: the behavior of a large, naturally fractured rock mass can differ significantly from the behavior of a small solid sample.

The finding may indicate that joints within the tower remain mechanically important at depth, rather than being limited to the visible surface. However, researchers must continue collecting observations before drawing broad conclusions about the tower’s internal structure. A short instrument deployment can reveal important vibration characteristics, but long-term monitoring is valuable for evaluating how those signals vary with wind speed, direction, temperature and seasonal conditions.

Scientists use similar methods around the world to study cliffs, alpine peaks, volcanoes and engineered structures. Ambient-vibration monitoring is especially useful because it can gather information without drilling deeply into a protected natural landmark. At Devils Tower, this approach provides a non-invasive way to learn more about the relationship between the formation’s columns and its overall response to environmental forces.

The Leaning Column and Natural Rockfall Monitoring

Devils Tower is continuously shaped by natural weathering. Water can enter fractures, temperature changes can widen cracks, and gravity gradually acts on rock along existing joints. Small rockfalls are a normal part of the evolution of steep cliffs and columnar formations, which is why the National Park Service monitors conditions in areas used by climbers and visitors.

One feature that has drawn particular attention is a leaning column near the Durrance Route, a well-known climbing route on the tower. The column is approximately eight metres tall and is visibly tilted relative to the surrounding rock. A U.S. Geological Survey report examined the area after a fresh flake was identified near its base. Monitoring marks were used to help identify any future surface changes.

That observation should be understood carefully. Monitoring a feature is a precautionary scientific practice; it is not a prediction that a major rockfall is imminent. Rockfall hazards at natural cliffs are assessed using visible fractures, weather conditions, past activity and continuing observations. Available public information does not support claims that Devils Tower is expected to collapse or that its measured vibration represents an immediate danger.

No person has documented the fall of a major Devils Tower column in modern recorded history. At the same time, geologists recognize that erosion and occasional loss of smaller rock material are natural processes over geologic time. The recent vibration research does not change that basic understanding. Instead, it provides a more detailed baseline for how the tower moves under ordinary environmental conditions.

Devils Tower’s Geological and Cultural Importance

Scientific interest in Devils Tower must be considered alongside its cultural importance. The monument is a sacred place for many Indigenous nations, who hold longstanding connections to the landscape and have their own traditional accounts of its origin. The National Park Service recognizes these cultural relationships and works with associated tribes in the stewardship of the site.

Devils Tower was designated the first U.S. national monument in 1906 under the Antiquities Act. Today, it is valued for geology, wildlife, outdoor recreation, cultural heritage and night-sky viewing. Its distinctive columns are also a major destination for technical climbers, although the National Park Service asks climbers to voluntarily avoid the tower during June in recognition of tribal cultural practices.

This broader context is important when discussing new research. The tower is not merely an unusual rock formation or a subject for dramatic headlines. It is a protected public landscape with scientific value and deep cultural meaning. Non-invasive monitoring can support conservation by improving understanding while minimizing disturbance to the landmark itself.

What the Measurements Mean for Visitors

For visitors, the central message is reassuring: the tiny movements detected by seismometers are consistent with the normal physical response of a tall, jointed rock formation to wind and background ground vibrations. The motion is too small to see, and researchers have not presented it as evidence of an impending failure.

The study is nevertheless significant because it shows what modern instruments can reveal about a familiar landmark. A formation that looks fixed and permanent can still provide measurable evidence of the forces acting on it. Wind, rock structure and seismic energy interact continuously, even when the landscape appears quiet.

Future measurements could help scientists compare conditions across seasons, evaluate the effects of unusually strong winds and refine models of fractured rock behavior. Such information may also benefit the study of other natural towers and cliffs where visible cracks alone do not tell the whole story.

Devils Tower will continue to change slowly, as all landscapes do. Its newly measured sway is not a sign of instability for the public to fear. It is a precise reminder that geological features are dynamic, shaped over immense spans of time by forces that can be subtle, persistent and scientifically revealing.

Sources

• National Park Service: Devils Tower formation and geology
• National Park Service: Devils Tower history and cultural resources
• U.S. Geological Survey: scientific information on geology and natural hazards
• U.S. Geological Survey: Devils Tower rockfall and stability assessment report
• Geological Society of America: Tower in Motion