Requirements to log the cache:
E-mail your answers to me: drmartin44@yahoo.com
Please do not post your answers in the log.
Who is in your group if one cacher is giving the answers for several people or groups.
1.As you drive up and away from GZ, estimate the slope of the mountian. It's impossible to face it or it will look as though it is straight up.
2.You are on Jenson Rd about the middle of the slide. The road is well maintained for any type of vehicle. Tell me how wide the slide is. You may want to use your car's odometer.
3.The end of the slide or the toe is west of Jensen Rd. Look all 360 degrees from GZ and tell me if you can recognize that there is an old slide here. Give me your reason for your answers. Don't forget to look at the toe and slide area when you come and leave GZ. Both roads at the end of Jensen heads back to the highway and you may want to use both to get a better perspective of the mountain and slide.
4.It is OK to take a picture of the mountain or surrounding evidence.
COLUMBIA MOUNTAIN SLIDE
About 12,000 to 15,000 years ago, 40 million cubic metric material slid off the west side of Columbia Mountain, covering an area of about 2 sq. kilometers of the valley floor. the top of the slide is 3,000+ feet above the valley floor. The slide is a V shape at the top, widening down to the valley floor. This was a period when the Flathead glacier was retreating back north. Indications are there was not much ice and snow on the valley floor at the time. The slide occurred in 2 parts without much time between. What caused the slide in the crux of Mr. Smith's study and possibly 4 factors were involved: Deglaciation: Fissures: Moisture: and the Steepness of the mountain. Let's look at the 4 factors.
During the last Ice Age a wall of ice moved down from Canada covering Flathead Valley with hundreds of yards of ice. As the glacier migrated south, it picked up and locked boulders and debris within the glacier. The tremendous weight of the ice pressing down and outward on the boulders and debris would turn them into huge matte of over sized sand paper and brillo pad that would gouge and scour anything it contacted. As the ice slowly melted and retreated, it revealed a new landscape that we now know as present day Flathead Valley.
The grinding of the glacier undercut the base of the west side of Columbia Mountain (just like a river undercutting a river bank). This section of the mountain was not made of of solid stone like granite but with a sedimentary rock called belted super group and was laced with fractures that were filled with stones and pebbles. This glacier would have supported the weakened lower section of the mountain until the glacier melted. Lacking its support of the glacier, the bottom of the mountain sloughed away.
It is impossible to tell how many or how large the fissures were as they fell to the valley floor. Mr. Smith and his team hiked to the top of the mountain and took pictures of the fissures and cracks above the slide. We can assume the lower fissures would be comparable (see picture). These fissures filled with smaller material would have allowed water to seep into the interior of the mountain. Do not forget there was more rain and snow during the period. The freeze and thaw cycle would have widened the fissures and cracks further weaken the mountain. Once the saturated ground gave way, the water would have also acted as a lubricant. Another important cause is the steepness of the face of the mountain. This would put more pressure straight down over the weakened base. Remember the goal of gravity is flatness. This slide is just the natural part of the rock cycle.
Mr. Smith gives this scenario. The weakened base of the mountain gave way first, soon followed by the upper part of the mountain. How soon is impossible to say. When a large slide occurs, seismic shocks would occur when the rock and debris hit the valley floor, this shock could have started the upper slide. The upper portion could have hung on a short time later, but gravity would win in the long run. Could a separate seismic shock start the bottom slide? Maybe, a 4.0 has been recorded in the past for that area. We do know one or all the factors came into play, because the results lie under your feet. Could a new slide happen again? YES!! Look at the size of the crack in the picture. Mr. Smith estimates a new slide will be almost as large as this one. When, is anybody's guess. Remember, time and mother nature will reduce this mountain to flatness.