Engineers designed the Moffat Tunnel for natural drainage, but a sudden East Portal flood from Crater Lake in 1925 still slowed progress to just 352 feet that February.
Moffat Tunnel Construction Happenings from 100 Years Ago
On Valentine’s weekend, Sunday, February 15, 1925—exactly 100 years ago today—progress on the water tunnel took a dramatic and unexpected turn on the East Portal side of the Continental Divide. When excavation reached 8,050 feet, a sudden breach in the rock unleashed a torrent of water—1,800 gallons per minute—gushing from a hidden seam.
The heading (excavation point) was located 1,100 feet beneath Crater Lake, and the immediate assumption was that the lake was the source of the deluge. However, the possibility remained that it could have originated from a subterranean stream, further complicating the mystery.
In response, a team was dispatched to Crater Lake to investigate. The weather was cloudy, with a low of about 5 degrees Fahrenheit. Acting on the advice of K. S. Weston, an electrician, they devised an ingenious—if unorthodox—experiment. After cutting through three feet of ice covering the lake, they introduced 10 pounds of chloride of lime into the frigid waters. To ensure the chemical dispersed thoroughly, they detonated a stick of dynamite, sending a shockwave rippling across the lake. Subsequent tests of the tunnel water confirmed the presence of the lime, linking the water’s source unmistakably to Crater Lake.
Despite local legends describing Crater Lake as ‘bottomless,’ soundings revealed its true depth to be only nine feet. The lake itself was never entirely drained. Over time, the once-raging flow diminished to 150 gallons per minute and eventually reduced to a mere trickle. By the following summer, with the lake replenished from snowmelt, the seam appeared to have sealed itself—perhaps aided by a combination of disturbed silt, mineral deposits, and shifting rock settling into the fracture.
Engineers anticipated the risk of water intrusion at any point and accounted for it in the tunnel’s design. The Moffat Tunnel was constructed as an apex tunnel, designed so that water entering at any point would be carried downhill by gravity toward an exit. On the East Portal side, where the flood occurred, the grade was 0.3%, allowing water to drain naturally and eliminating the need for pumping. The West Portal side, which was unaffected by the flood, had steeper grades of 0.9% and 0.8% to ensure efficient drainage in that direction.
However, even with the tunnel’s self-draining design, the volume of water on the East Portal side still posed a significant challenge. The flooded section required meticulous handling, and the persistent flow of water slowed progress to a crawl. Meanwhile, on the West Portal side, unstable ground conditions created additional obstacles, further limiting excavation. Workers managed only 352 feet of progress in February, hindered by waterlogged conditions and difficult terrain.
This episode underscores the sheer unpredictability of tunneling under such rugged conditions. While the flood was a setback, it also showcased the ingenuity and persistence required to push forward—qualities that defined this ambitious project and its workers.
This is just one of many remarkable episodes that shaped the history of Rollins Pass and the Moffat Tunnel. We explore more of these challenges, surprises, and triumphs in our second book on Rollins Pass.
Today’s story is just one moment in a much larger epic. Follow our blog as we track the centennial of the Moffat Tunnel’s construction and opening through February 2028, uncovering more stories along the way.
Nota Bene: The remarkable photograph accompanying this post captures the waters of Crater Lake pouring into the Moffat Tunnel. Like many others in our collection, it offers a rare glimpse into the past and has been meticulously preserved. Carefully scanned from the original, it retains its historical integrity, ensuring that every detail—from the texture of the print to the subtle interplay of light and shadow—is faithfully rendered.
B. Travis Wright, MPS | Preserve Rollins Pass | February 15, 2025
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