A storm unfolding in two acts
When you think of Hurricane Camille, perhaps you may recall a popular song of the era, with these lyrics:
Long as I remember The rain been comin’ down. Clouds of myst’ry pourin’ Confusion on the ground. Good men through the ages, Tryin’ to find the sun; And I wonder, Still I wonder, Who’ll stop the rain.
The group was Creedence Clearwater Revival, and the song debuted in January 1970. While not directly mentioning Camille, there remains the curiously ironic lyric: “Went down to Virginia seeking shelter from the storm.”
You may also recall that Camille was a Category 5 hurricane that struck Mississippi and Louisiana. Camille raised one of the largest storm surges ever to batter the Gulf Coast (24 feet) and over 150 lives were lost due to surge and freshwater flooding over southern Mississippi. This storm was one of only three Cat 5s to strike the U.S. during the 20th century. In and of itself, the tremendous loss along the Gulf Coast qualifies as an outright disaster.
But days after landfall, Camille had a card yet to play. After moving inland on Aug. 17, the storm rapidly weakened and the heavy rains abated. On the 18th, the post-tropical vortex hooked due east across the lower Ohio Valley, as the circulation was picked up by the westerly jet stream. Spotty pockets of 1 to 3 inches fell in a broad arc from northern Mississippi to West Virginia.
Late on Aug. 19, the remnant low crossed the Appalachians. The evening’s weather map appeared humble; the low had a couple of closed isobars and a central pressure of 1007 millibars, and the storm was clearly on the move. The Weather Bureau’s overnight forecast for central Virginia called for “showers, with clearing in the morning”.
No one, not even the Weather Bureau, seemed concerned. After all, who in Central Virginia would expect a record-smashing, tropical deluge from hurricane remnants approaching from the west, nearly three days after landfall?
Then, after sunset, a hellish rainstorm exploded over the eastern slopes of the Blue Ridge Mountains, focusing down to just a pinprick on the map, centered squarely on Nelson County.
Act Two of Camille’s tragedy began to unfold.
As shown in the image below, Camille’s rain swath was unusual, oriented perpendicular to the Blue Ridge, and exceedingly narrow. There were distinct rainfall maxima located over the eastern slopes of the Appalachians and the Blue Ridge. This suggests a classic mechanism at play, involving sustained, upslope flow of moisture. (A third maximum, less pronounced, lay over the Piedmont downwind of Albemarle County’s southwest mountains).
But the rain was hyper-concentrated over Nelson County, where an official total of 27 inches was recorded. This is near the foot of the Blue Ridge proper, an imposing rampart exceeding 4,000 feet elevation is spots. And the rain totals may have been even higher, as the following account suggests:
Sheriff Whitehead talked about a farmer who lived beneath the epicenter of the very heaviest rains. ‘He had been feeding cattle and had four or five barrels, 155 gallon drums, on the back of his pickup. The next morning those barrels were nearly full of rain, 31 inches.’ (J. Halverson, Queen of Rains, Weatherwise).
It staggers the mind that all of this heavy rain fell in the interval between sunset and sunrise. If there was a theoretical maximum amount of rain — given optimum alignment of high moisture, vigorous uplift and sustained intense thunderstorms — nature had collocated all its forces, exactly so, to create it.
Using the latest available historical data, we have been able to more precisely place rainfall totals at certain points and produce a more zoomed-in rainfall map against terrain, landslides and debris flows.
This map presents a very detailed overlay of the rain contours (isohyets) on top of terrain contours and landslide locations. Anne Witte of the Virginia Division of Mines, Minerals and Energy has located over 3,730 individual landslides (shown by small red “+”), with the precision of airborne lidar.
In some locations, there is perfect concordance between extreme rain accumulation and dense coverage of landslides. In other regions, the relationship is less clear. Understanding the discrepancy is the subject of an ongoing study.
Nature’s perfect rain-making machine
Such an alignment involved many scales of motion. Let’s treat the larger processes first.
First, there was the remnant vortex, drawing in low-level moisture, converging the air, creating uplift. Contrary to popular belief, the vortex did not stall — it could not have — since it was embedded in the fast-flowing jet stream aloft.
Second, a cold front, oriented west to east, sagged southward through Central Virginia. This front, more than any other element, helped to concentrate the rainfall into a long, narrow ribbon cutting across Virginia.
Third, the jet stream’s flow focused the uplift further. Embedded within the flow was a pocket of fast wind, termed a jet streak. Airflow undergoes dynamic adjustments as it traverses a jet streak — and this lead to a small bull's eye of vigorous ascent over central Virginia.
Fourth, low-level moisture was exceptionally abundant. The summer was rainy, and both soil and vegetation liberated large fluxes of water vapor into the overlying air. Humidity accumulated above the surface, raising dew points across southern Virginia and north-central North Carolina into the 76 to 78 degrees range. Thick moisture pooled south of the cold front, and along the lee slopes of the Blue Ridge.
These four factors, in and of themselves, can create a great rainstorm, over a broad area. However, to get the laserlike, hyperfocus of rain over parts of Nelson County, you need intense atmospheric motions on a much smaller scale: Those of thunderstorm cells, swollen with so much water that they generate torrential cloudbursts.
On these very small scales, we know that there was a cluster of thunderstorm cells locked up against the high terrain. The radar could only see their high tops (being 80-100 miles distant) but we also know that this aggregate of thunderstorm cells did not move for many hours. Think of this mountain-locked cluster as a “storm within the storm”.
Why did it remain stuck? The thunderstorm complex was fed by a strong, moist inflow from the east and southeast, at low levels. In the “crook” (intersection) of the Blue Ridge and cold front (a.k.a. Nelson County), moisture was funneled rapidly upward. Within the cloud complex, individual storm cells matured, moved off the mountain range and dissipated, but new cells formed immediately upwind. This genesis point remained locked to the terrain, for hours. The repeated passage of cloudbursts across Nelson County constituted a train of cells, sustained for nearly eight hours. It was a bucket brigade unlike any other ever experienced.
By daybreak, when Camille’s parent vortex departed the Blue Ridge, the region of moisture convergence shifted away from the mountains. The jet streak advanced into New England. The cold front pushed into North Carolina. Low-level winds turned from the west, now downslope, evaporating and dissipating the rain machine.
But all that tremendous heat energy, released from the condensation of trillions of gallons of cloud water, rejuvenated the parent vortex; it began intensifying over eastern Virginia, becoming a tropical storm once again over the Atlantic.
And only at daybreak did those still alive in Nelson County realize the true horror of the night.
A landscape ripped apart and liquefied
The verdant, mountainous landscape was ravaged by sheets and blasts of flowing water in the extreme. The entire veneer of mountain sides was stripped away whole, revealing ancient, naked bedrock.
To this day, massive debris scars or “chutes” remain. Drive the back roads of Nelson County, and occasionally you will see long, vertical strips of rock laid bare, along mountain summits, contrasting starkly against the lush forest. These scars mark the location where entire mountainsides sloughed away.
Amid streams turned into muddy torrents, entire hill slopes liquefied into fast-flowing sheets of mud. Soil, rock, boulders, stands of trees and thickets and scrub, all manner of creatures, flowed down the mountain. These flows concentrated in hollows where hill slopes converged. Debris jams formed and then explosively gave way. Homes perished. Roads disappeared. Bridges were swept away. Countless trillion tons of water and soil and forest consolidated into black waves that effectively erased the face of central Nelson County.
In the dead of night, amid the deafening roar of sheeting rain and surging floodwater, how did lucky survivors recognize the landslide danger? There was the nearly continuous, strobe-like effect of lightning that provided some visual guidance of nearby, surging waters. But the account of Curtis Matthews, a resident of Nelson County, is most striking:
The scent of crushed pine amidst the roar of the mudslides, invisible in the storm, was what saved my life. I had gone in to lay down for a while, and when I came back out to the porch, I smelled the unusual odor of bark and sap and green timber. I’m in the logging business and I know that smell, but never in my life smelled it so heavy, even in a sawmill. The air was thick with it every breath you took. It was like sticking your head in a sack of bark…in 20 minutes, the water rose from three to eight feet in my yard…it must have been all these trees coming apart and washing down the hollow that I smelled. (Reported by Ken Ringle, Associated Press).
The body count was between 150 to 160 souls — women, children, men, the elderly. Drowned and crushed bodies were recovered from tangles of uprooted trees heaped in the middle of swollen streams. Several individuals to this day remain entombed beneath feet of mud and rock, their exact whereabouts forever unknown.
Link: Photographs of Camille’s destruction in Va. from the University of Virginia Library
The liquid soil and mountain rock and floodwater flowed through Davis Creek, the Tye and Rockfish rivers, which converge into the James, headed east toward Richmond, thence into the Atlantic Ocean. The peak river discharge reconstructed by hydrographic analysis was estimated at 36 million gallons per minute. Thus Camille’s remnants officially established the U.S. record river discharge for streams east of the Mississippi River.
Could it happen again?
Yes. Terrible flood catastrophes repeatedly unfold in a region where high terrain, unlimited Atlantic moisture and tropical energy frequently coincide. The notion that Camille was an extremely rare, “1000-Year Storm” doesn’t seem as credible, when only 26 years later and 60 miles away, another flash flood/debris flow/record-discharge event developed in Madison County, Va., in June 1995. Once again, a stubborn thunderstorm complex developed along a stationary front, and got locked up along the mountainside.
Geological analyses have uncovered remnants of similar catastrophes all along the Blue Ridge. These high magnitude events are likely the modus operandi by which the ancient Appalachians swiftly denude, accomplishing thousands of years of otherwise slow, steady erosion in a single day or night.
Climate change is here. Water vapor levels in the atmosphere have increased, as demonstrated by trends in radiosonde (weather balloon) data. Rain events over the eastern United States have been characteristically more intense, as demonstrated by numerous studies.
Our vulnerability to flash floods is now higher than ever, and this vulnerability lies at the intersection of land-use changes, an accelerating water cycle, and the immutable mountains. Future flash flood and landslide disasters along the Blue Ridge will happen…not necessarily in the exact same spots, but with increasing frequency along the mountain range.