Out of the Ashes: Giant Rainbows

Out of the Ashes: Giant Rainbows

On May 18, 1980, Mount St. Helens erupted with the force of 350 megatons of dynamite. The blast denuded 230 square miles of forest and sent 1.4 billion

On May 18, 1980, Mount St. Helens erupted with the force of 350 megatons of dynamite. The blast denuded 230 square miles of forest and sent 1.4 billion cubic yards of ash 15 miles into the sky. To say that the eruption was cataclysmic would be an understatement.

Right in the path of the ash cloud and landslides that accompanied the eruption sits Spirit Lake, just four miles from the mouth of the volcano. The blast transformed Spirit Lake from a picturesque alpine lake into a lifeless soup of muck and fallen timber.

But in the 30 years since the eruption, Spirit Lake has undergone a dramatic transformation. Ironically, the very rock and debris that smothered Spirit Lake have ensured its rebirth. The eruption and landslides deposited abundant minerals and nutrients into the lake, and these have provided the raw materials to fuel a rich ecosystem. Once the silt settled and the water column cleared, ecological succession began: bacteria to phytoplankton to zooplankton, followed by aquatic insects and amphibians. And into this fertile mix rainbow trout were reintroduced in the early 1990's with amazing results.

"Make no mistake about it," says Charlie Crisafulli, a Forest Service biologist who monitors Spirit Lake, "for a high-elevation lake the fish are quite big." To wit: 20-24 inches, 4-8 pounds. Quite big, indeed.

Crisafulli and his colleagues have collected data on these fish and their findings are surprising. "The age structure is something odd. The fish grow fast and appear to die young," Crisafulli says. In fact, the vast majority of the fish appear not to live past five years, which means, of course, that these fish can grow from a fry to 8 pounds in five years.

Another anomalous thing about the Spirit Lake rainbows is their reproductive behavior. Despite extensive surveys for spawning beds along the lake's shore and in a small feeder creek, spawning has never been documented.

Nevertheless, "The fish have to be reproducing because they have now been persisting for 16 years," says Crisafulli. "The mystery is where the fish are spawning." But he has a theory: Much of the lake's bottom consists of pumice deposited during the eruption, and in many places, cold spring water seeps through the porous rock. Crisafulli thinks the trout may actually spawn in the current created by these upwellings, even at depths of 5 to 15 feet. Crisafulli and his team will investigate this further.

If there is a downside to this story, it's that you can't fish in Spirit Lake. It is designated as a scientific site to observe and document the changes in the ecosystem. However, nearby Coldwater Lake is open to fishing--and it too is home to some very large fish.