The story of Crater Lake centers on the
destruction of a large volcano, Mount Mazama, and the subsequent
accumulation of a deep blue body of water in its place. The events
preceding and immediately following a final eruption of this volcano
occurred at a time when Native Americans had already established
themselves in the region. Whether the tales about the origin of Crater
Lake told to the pioneers a century ago by the Indians actually date
from prehistoric times may never be known. The stories describe a
powerful spirit living beneath the mountain which the Klamath people
called Llao. When angry,
Llao would journey toward the surface and sit atop the mountain to
speak with a voice like thunder. It is difficult to trace the
relationship between these people and the spirit since this began so
long ago. The occurrence of thunder is another matter.
Thunderstorms are more a phenomena of
summer than winter in the region around Crater Lake. Winter
thunderstorms are not unknown, but snowstorms are much more common. That
is not to say that thunderstorms are common in the park during summer.
If anything, these weather events are more of an exception. Summer
weather is usually mild during July and August. Daytime highs are mostly
in the mid to upper 70s and night time lows are in the 40s. A high
pressure system aloft, the Pacific High, dominates our summer climate.
The resulting warm and dry surface conditions at the higher elevations
are ideal for camping and sightseeing from July to September.
Summer thunderstorms arise when
moisture is lifted to form the tall cloud type called cumulonimbus.
This happens when an upper level low pressure system located offshore of
northern California directs moisture inland and across the Cascade
Range. Thunderstorms can also occur in the area when moisture is drawn
in a northerly direction along the western edge of high pressure
centered over Nevada or Utah.
What happens inside the growing cloud
to separate static charges, with a thunderstorm being the eventual
result, is thus far imperfectly known. What we do know is that charges
separate with the cloud's base becoming negatively charged and the
ground or water body below being positively charged. Since the air acts
to insulate the charged cloud droplets, a potential of 3,000 volts per
meter can develop prior to a lightning strike. The lightning bolt is
electrical current connecting the ground or lake surface with the cloud
base in order to neutralize the charge separation (lightning can also
connect clouds to one another and isolated cells within a cloud). The
flash of lightning, which lasts for less than a second, heats the nearby
air to over 10,000 degrees Fahrenheit. The rapidly expanding air travels
at supersonic speeds and produces a shock wave we hear as thunder. This
sound is louder the closer an observer is to the discharge. Thunder is
rarely heard if the observer is more than 12 miles away, even when the
lightning is clearly visible. To estimate distance from a discharge,
some people count between seeing a flash and hearing thunder. If five
seconds elapsed between the lightning and subsequent thunder, then the
discharge occurred about one mile away from the observer.
Lightning is attracted to high spots
around the rim of Crater Lake since the distance between cloud base and
surface is less. Since many park trails ascend points such as Garfield
Peak, Mount Scott, and the Watchman, hikers should keep a watchful eye
to the sky on days when cumulus clouds fill the air. As a safety
measure, weather forecasts are posted at the two visitor centers each
morning. In addition to trees and rock outcrops around the rim that
attract lightning, Crater Lake can be struck by discharges from the
clouds. Water conducts electrical charges easily, and with a surface
area of roughly 25 square miles, the lake presents quite a target.
Lightning strikes over the park can be
an awesome display of nature's power. The associated thunder can fill
the old glacial valleys of Mount Mazama and put fear into animals as
well as humans. During a brief episode of thunder and lightning, as the
wind bends the trees and marble-size hail pounds the ground, the ancient
story of Llao
comes to mind, reminding some of us that great power is nearby and can
shake the earth.
Tom McDonough teaches science at
Chemeketa Community College in Salem, Oregon, and has been a seasonal
naturalist at Crater Lake since 1969.
Karl J. Belser in Ernest G. Moll, Blue Interval,
Portland: Metropolitan Press, 1935, p. 26.