Lewis and Clark's mountain 'cannon'
Camped at the Great Falls of the Missouri in July 1805, Meriwether Lewis repeatedly heard booms from the west 'resembling precisely' a six-pound cannon three miles off; Clark wrote that 'the Cause we Can't account'.
1805 CE · 47.53, -111.29 · status: unexplained
The account
Lewis noted that the Native people had told the expedition of such noises in the Rocky Mountains. Similar unexplained 'skyquakes' are reported worldwide under names like mistpouffers and barisal guns.
The sceptical view
Candidates include distant thunder, rockfalls or bursting ice; no single cause has been shown for the class of sounds.
The researched reading
A genuine, well-recorded sound heard by careful observers. Distant thunder, rockfalls or bursting ice, carried far by the atmosphere, are the likely causes. The cause is not known, but nothing suggests it was exotic.
| Explanation | Weight | Why |
|---|---|---|
| A known natural phenomenon | 40% | Distant thunder over the Rockies, rockfalls, or ice and rock bursting in summer heat are all known to sound like distant guns. Mistpouffers and other “skyquakes” are a worldwide class with several ordinary causes, including distant storms and coastal surf. |
| Undetermined | 30% | The share a generic explanation had beyond what has been shown for this case: it fits many cases like this one, but has not been demonstrated for this one. |
| Something in the surroundings | 12% | Temperature inversions over the plains can carry low-frequency sound for very long distances and hide its direction. A far-off source could then seem like a cannon three miles away. |
| A cultural story | 6% | Native accounts of mountain noises primed the expedition to notice and record the sounds, but the journals record them first-hand. |
| Perception, memory or mind | 5% | Several men heard the sounds on different days and wrote them down at once, so misperception is unlikely to explain them. |
| Genuinely anomalous | 5% | The source was never identified, and some skyquakes remain unexplained. However, ordinary candidates are plentiful. |
| A hoax or fabrication | 2% | The journals were private working records with no motive to invent this. |
Official position: No investigation; Lewis and Clark recorded the sounds as unexplained.