52 Volume 30 – 1999


Volume 30, 1999

All material courtesy of the National Park Service.These publications can also be found at http://npshistory.com/
Nature Notes is produced by the National Park Service. © 1999


By Stephen R. Mark, Editor

Work on a new fuel line and the Cleetwood Cove Trail prevented last year’s visitors from fishing or taking boat tours, so the summer of 1999 promises a return to Crater Lake. Not since 1952 had a whole season passed without public access to the water, so it seemed fitting to begin this edition of Nature Notes with articles about the lake and the spectacular geological story it represents.

As anyone who has experienced the beauty found in its forests, wet lands, and even barren areas will readily attest, there is more to Crater Lake National Park than its central feature. Since each part of the park contains something of interest, Nature Notes is devoted to providing visitors with information they might not otherwise obtain on their own. In this edition, for example, there are articles on how to identify the various sedges, a rare wildflower called Mount Mazama collomia, and why weather plays a some times defining role in the visitor experience.

Change occurring over the length of one, possibly two, lifetimes is the common thread among the last three contributions. One article touches on the importance of memory to continuity in the park, while another piece about the habits and management of bears is essentially a retrospective. The last article describes what can be found in the seemingly mundane area around Whitehorse Creek in order to emphasize that repeated visits often result in new understanding about a place.

Nature Notes from Crater Lake is made possible by the Crater Lake Natural History Association, now in its 58th year. It sponsors this publication as part of an ongoing commitment to support the educational and resource management programs of the National Park Service. Please join them in this effort by becoming a member of CLNHA and receive a 15 percent discount on items sold in the William G. Steel Center at Park Headquarters or at the summer visitor center located in Rim Village.

NPS photo by George Grant, 1936.

Born of chaos, fire and smoke,
Turbulent nature did’st invoke
Mazama’s fall—that thou should’st be
Silent, mysterious, sapphire sea.

Belle Menefee Meyer, 1941

Wizard Island and Llao Rock by Karl J. Belser.

Answers from the Deep

By Tom McDonough

Crater Lake is certainly a sight to behold. It is especially spectacular for those who see it for the first time. Pictures cannot really capture the lake’s magnitude and its image seems ageless. The base of the great volcano, which stood here once, properly frames the cobalt blue of the lake. These rugged cliffs are mostly bare, undoubtedly stripped of vegetation by continual rockfall. What of Wizard Island? It somehow seems fitting to have a winged dinosaur fly in circles around the cone. These creatures were long gone, however, when the fires of Mount Mazama first began to burn less than a half million years ago.

The apparent serenity of this lake is somewhat misleading. We must face the reality that this image is fleeting, or in the geologic time scale, ephemeral. Why should we expect Crater Lake to always be the same when it has changed so much in the past? A deep lake with a small volcanic island near one shore are its dominant features, though how each formed has been somewhat of a mystery until recently. By analyzing lake sediments obtained from the bottom, scientists can now tell us much more about what has happened here since Mount Mazama last erupted 7,700 years ago.

This crater (or caldera) holding Crater Lake today was created by a great eruption. That event ended with the collapse of the mountain summit, and was much more catastrophic than the Mount St. Helens incident in 1980. It may have been the biggest occurrence of its kind in North America during the last several million years. During the eruption, Mount Mazama released great quantities of ash and pumice. At least 12 cubic miles of mountain top disappeared as it slumped back into a drained magma chamber located beneath the volcano, now below the lake bottom.

During the summers of 1988 and 1989, a piloted submersible was used for the first time to explore the bottom of Crater Lake. Videos identified active thermal springs on the caldera floor, indicating the presence of heat below. Hot water rises up, in various locations, through layers of lake sediment that have accumulated since Crater Lake formed. Five sediment core samples were taken from selected sites on the lake bottom during these dives. The sample taken east of Wizard Island, on a series of lava domes called the Central Platform, lacks the rock debris covering other sites and therefore better displays the materials that have settled here from above. These include volcanic ash, soot from forest fires, pollen grains, and diatoms layered in a fine mud about five feet in depth. By looking closely at this core sample, geologists can now work out what kind of events have transpired in and around the caldera over the last several thousand years.

Diagram courtesy of U.S. Geological Survey.