Mount Shasta in 1786

La Pérouse's Account and the Mystery of the Fire

In 1786, a French explorer sailing off the California coast saw fire on Mount Shasta's summit and reported it to the world. For more than two centuries, this single observation shaped how people understood the volcano's recent history. It became "evidence" of an 1786 eruption, cited in books and articles, passed along in legend and lore.

Except the reality of what La Pérouse saw—and what it actually means—is far more interesting than the simple narrative of "volcanic eruption in 1786."

His account is a window into how volcanic history gets written, how a single observation can echo through centuries, and how we distinguish between what really happened and what we thought happened.

Who Was La Pérouse?

To understand La Pérouse's sighting, you need to know who he was and why he was sailing past California in the first place.

Jean-François de La Pérouse was a French naval officer and explorer, born in 1741. By the 1780s, he had already established himself as a skilled navigator and scientific explorer, commanding expeditions to distant parts of the world. In 1785, he embarked on his most ambitious voyage yet: a circumnavigation of the Pacific Ocean with the goal of exploring the northwestern coast of North America, mapping uncharted territory, and gathering scientific data.

This was during a period of intense European interest in the Pacific Northwest. The Spanish, British, and French were all competing to map and claim territories along the California and Pacific coasts. La Pérouse's expedition was partly exploration, partly national prestige, partly scientific curiosity. He carried naturalists, artists, and instruments designed to document everything he encountered.

The expedition left France in August 1785. By 1786, after a long journey across the Pacific, La Pérouse's ships were sailing down the California coast, having passed through the Aleutians and Alaska. On September 6, 1786, his fleet was off the coast of northern California, in the vicinity of what is now Monterey Bay—far enough away to see the Cascade Range inland.

The Account: What La Pérouse Reported

La Pérouse kept detailed journals of his voyage. In his account of September 6, 1786, he wrote that he observed what appeared to be volcanic fire on a high mountain inland. He described seeing flames or fire on the summit, visible even during daylight. The observation struck him as significant enough to note it in his expedition records.

The exact wording matters: La Pérouse reported seeing "fire," but he was viewing it from a moving ship, at significant distance, under specific atmospheric and lighting conditions. He was an explorer and navigator, not a volcanologist. He saw something burning on a mountain and reported it accordingly.

For La Pérouse, this was one observation among thousands during his voyage. He documented coastlines, indigenous peoples, natural resources, and hazards. A fire on a distant mountain was noteworthy but not the focus of his mission. He recorded it and moved on.

Why It Became an Eruption

Here's where the story gets interesting. La Pérouse's account might have remained a curious historical footnote—a single explorer's observation from 1786—except for what happened next.

Over the following decades and centuries, as more people became interested in Mount Shasta and volcanic activity in California, La Pérouse's sighting got cited again and again. Historians and geologists would reference it as evidence of recent volcanic activity. It became "the 1786 eruption of Mount Shasta," a commonly accepted fact in the volcanic history of the mountain.

Why did it stick? Several reasons. First, it was the most recent written account of Mount Shasta's activity by a credible, literate observer. Before photography and scientific instruments, written accounts from explorers were the primary historical record. If a French naval officer said he saw fire on Mount Shasta, that carried weight.

Second, the timing seemed plausible. Mount Shasta's known eruption before 1786 was around 3,200 years ago. A more recent eruption fit the narrative of an "active" volcano. The 1786 sighting filled a gap in the record.

Third, scientific understanding of Mount Shasta was limited for most of the 1800s and early 1900s. Systematic geological study of the volcano didn't begin in earnest until the mid-20th century, when researchers could actually examine rock layers and date volcanic deposits with precision. For the century-plus before that, La Pérouse's account was one of the few historical anchors people had for "recent" volcanic activity.

So the 1786 eruption entered the record not because scientists had confirmed it through geological evidence, but because a historical account survived and got repeated.

The Scientific Investigation: What the Evidence Actually Shows

When modern geologists finally turned their attention to the question of whether Mount Shasta actually erupted in 1786, they found something unexpected: no geological evidence for a 1786 eruption.

They examined rock layers, ash deposits, and dated materials from that time period. They looked for the kind of deposits you'd expect from a 1786 eruption—fresh lava flows, ash layers with that age signature, charred vegetation, mudflow deposits. Nothing. No clear evidence of volcanic activity on Mount Shasta in 1786.

This doesn't mean La Pérouse was lying or hallucinating. It means he saw something on that mountain, but the geological record doesn't support a volcanic eruption as the explanation.

What the rock record does show is that the most recent confirmed, well-documented eruption of Mount Shasta occurred around 3,200 years ago. Everything between then and now shows no clear evidence of major volcanic activity. There are hints of possible, uncertain activity in the 1,800–200 year window (as we covered in the Eruption History post), but nothing definitively tied to 1786.

In other words, La Pérouse didn't see an eruption. He saw something that looked like fire to him, but it wasn't magma and lava fountaining from the summit.

What Can You Actually See from the Ocean?

This raises the question: if not a volcanic eruption, what could La Pérouse have seen?

The leading hypothesis among geologists and historians is straightforward: he saw a wildfire.

This might sound like a downgrade from "volcanic eruption," but it's actually more plausible given the context. Northern California in September is wildfire season. The landscape is dry. Mount Shasta's slopes, especially at lower elevations, support forests of fir and pine. A fire burning on the mountainside, especially one on the high slopes with good visibility from the ocean, would look like flames and smoke from a distance.

But here's the key: from La Pérouse's vantage point—a ship sailing off the coast, viewing the mountain from 50+ miles away—it would be nearly impossible to distinguish between different types of fire. A wildfire burning on the slope would appear as flames and smoke. A volcanic eruption would do the same. Both would look like fire on the mountain from a ship at sea.

Factor in the time of day, atmospheric conditions, the angle of viewing, and the limitations of human perception from that distance, and it becomes easy to see how a wildfire could be interpreted as volcanic activity by an observer unfamiliar with the region's fire ecology.

The 1786 date also happens to fall during California's documented history of large wildfires. The region experienced periodic fire events, especially in dry years. A wildfire in September 1786 on Mount Shasta's slopes is far more probable than a volcanic eruption that left no geological trace.

What This Teaches Us About Volcanic History

The La Pérouse account is a perfect example of how volcanic history gets written and rewritten as new evidence emerges. For over a century, this sighting was accepted as fact—the 1786 eruption of Mount Shasta. It appeared in books. It shaped how people thought about the volcano. It became history.

But when geologists could finally examine the actual rock record with precision, the narrative changed. Not because La Pérouse was wrong about seeing something, but because what he saw could be better explained by something other than volcanic eruption.

This is an important lesson: historical accounts and geological evidence sometimes diverge. A credible observer can report something real without that something being what we initially thought it was. Volcanic history isn't written just in eyewitness accounts; it's written in stone, ash, and datable materials in the earth itself.

The 1786 sighting also illustrates how hard it is to distinguish fire sources from a distance. Mount Shasta has had both volcanoes and wildfires. Both produce fire, smoke, and dramatic visual effects. Without closer investigation, without the ability to examine what actually happened, the two can look identical to an observer miles away.

For curious visitors hiking Mount Shasta today, the La Pérouse story offers something valuable: a reminder that what we think we know about volcanic activity can change as we learn more. The 1786 eruption that appeared in history books for two centuries probably never happened. But that doesn't make La Pérouse's sighting less real. It just makes it something different than what two centuries of people assumed it was.

The Real Timeline

So where does this leave Mount Shasta's eruption history? The takeaway is straightforward: the most recent confirmed volcanic eruption on Mount Shasta was around 3,200 years ago. The 1786 sighting, while intriguing, doesn't change that timeline. There's no geological evidence of eruptions in the last few centuries, despite La Pérouse's observation.

The mountain has been quiet for 3,200 years—a long silence in geological terms, but not an eternity. It's still alive, still hot, and still capable. But it's not actively erupting, and it probably wasn't erupting in 1786 either.

Want to understand the full context? Explore Mount Shasta's complete eruption history and whether it's active today.