The Ventura Gem & Mineral Society, Inc. (VGMS)

Geology 1996 Archive.

Table of Contents.

1. AUGUST - ON-LINE GEOLOGIST,
2. OCTOBER/NOVEMBER - Inyo County - High and Low,
3. DECEMBER - YOSEMITE LANDSLIDE: CAUGHT IN THE ACT.

August.

ON-LINE GEOLOGIST, From Livermore Lithogram 2/96.
     The USGS is offering a new experimental on-line service called ASK A GEOLOGIST. Anyone with internet access can send their questions about Earth Science to the USGS via electronic mail, and the question will be answered in a day or two by a USGS geologist.

The e-mail address is:
     ask-a-geoligist@octupus.wr.usgs.gov.

          Reprinted from CFMS Newsletter, August 1996.

Table of Contents.

October/November.

Inyo County - High and Low.
     Inyo County is gifted in having both the highest topographic relief (in the contiguous States) and the lowest elevation in all 50 states. Mount Whitney rises above all other peaks in the Sierra Nevada Range to an elevation of 14,494 feet above sea level. In contrast, a portion of the Death Valley playa is 282 feet below sea level in an area 4 miles west of Badwater. This represents a difference in elevation of 14,776 feet. The lowest point in Death Valley is only 90 miles southeast of Mt. Whitney.

Three of the best locations to view this "contrast in elevations" is on Telescope Peak or Mohogany Flat in the Panamint Range or at Dante's View in the Black Mountains. The best vantage point is on Telescope Peak which rises 11,049 feet above the floor of Death Valley. If you look out from Telescope Peak to the northeast approximately 15 miles you will be observing the lowest portion of the playa which represents an 11,331 foot elevation difference within Death Valley (between Telescope Peak and the lowest portion of the playa). If you look to the northwest, you will see the Sierra Nevada skyline on the horizon and perhaps you can distinguish Mt. Whitney from the other high peaks. On a clear day, with a single glance, one can view both Mt. Whitney and the Death Valley playa and literally see the "highest and the lowest".

It is also possible to view this phenomenon in other locations along the crest of the Panamint Range and on the higher peaks of the Black Mountains, Funeral Mountains, and the Cottonwood Mountains which surround Death Valley.

The Sierra Nevada Mountain Range and Death Valley are part of the Basin & Range geomorphic province which extends east from the Sierra Nevada to the Wasatch Range in Utah. The most striking characteristic of the Basin & Range is the north-south trending series of high mountains and relatively low valleys formed by tensional tectonic forces.

Steve Mulqueen,
September 26, 1996.

Table of Contents.

December.

YOSEMITE LANDSLIDE: CAUGHT IN THE ACT;
Deadly slide is glimpse of process that shaped Yosemite National Park.
     When 162,000 tons of granite suddenly broke free of a cliff in Yosemite National Park last July, rock climber Ed Youmans was there to witness the awesome event and capture it on film.

The landslide, which occurred on July 10, created an "air blast" that felled hundreds of trees. This event gave geologists a rare glimpse at the processes that have sculpted Yosemite's landscape over millions of years. But tragically, the disaster also killed a hiker and injured 14 other people.

At 6:52 p.m., the moment the landslide came crashing down, Youmans was ascending Washington Column, about 1.5 miles from Glacier Point. He heard a loud crack. "At first I thought it might be thunder," he recalls. "Then I realized it was way too loud to be thunder." He turned and saw "house-size boulders bouncing down the face of Glacier Point.... I just stood there with my mouth open. I couldn't believe it."

A huge irregular chunk of rock with a volume of about 80,000 cubic yards plunged a third of a mile toward the valley floor. It originally measured almost 500 feet wide and about 30 feet high and 20 feet thick; as it fell, it broke up into many smaller pieces. Accelerating to 160 miles per hour, the rock mass displaced the air in front of it, generating the gale-force air blast. "It felt like an earthquake and sounded like cannon fire," says tourist Bill Leavengood of St. Petersburg, Florida. The landslide damaged the Happy Isles Nature Center and the air blast mowed down much of the adjacent forest, up to 2,000 trees over 11 acres, estimates Ray Wilson of the U.S. Geological Survey in Menlo Park, California.

A falling tree hit and killed 20-year-old Emiliano Morales of Montebello, CA. Other victims were treated for bumps, bruises and dust inhalation.

The actual mass of the rock remains uncertain but may have been as much as 162,000 tons, says landslide expert Gerry Wieczorek of the USGS in Reston, Virginia. About half of Yosemite's landslides are triggered by events such as earthquakes or rainstorm-hastened erosion, Wieczorek notes.

Over time, rock layers "exfoliate" from Yosemite's dome-shaped granite masses like the layers of an onion. But whatever triggered this latest landslide, it was apparently too subtle to have been forecast.

Landslides are by no means unheard of in Yosemite. The most recent big slide happened in 1987, when about 600,000 cubic yards of rock fell 1,500 feet from Middle Brother spire. That rock fall caused no air blast, however. Apparently an air blast occurs only under certain conditions. A falling chunk of rock must remain together long enough to shove air out of it's way, Wieczorek says.

He notes that the park's grandest prior air blast was in 1872, when an earthquake triggered a rockfall that knocked down a park inhabitant and moved his house a couple of inches.

     By Keay Davidson,
     EARTH - December 1996,
     Contributed by Steve Mulqueen.

Table of Contents.

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