GC5DHR0 ICE - Pushy Attitude!
Type: Earth | Size: Other | Difficulty: | Terrain:
By: kekj @ | Hide Date: 10/11/2014 | Status: Available
Country: United States | State: Colorado
Coordinates: N39° 01.453 W108° 01.615 | Last updated: 08/30/2019 | Fav points: 0
           

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Grand Mesa glacial activity is a hotly debated subject. One would expect glaciers to develop and flow down the sides of a mountain, but what about on top of a "flat topped" mountain such as Grand Mesa? What evidence of glaciers is there? - - You be the judge and decide!

A short hike over moderately rough terrain to see what ICE with a "Pushy Attitude" might have done.

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(While not required, a review of nearby "Grand Mesa's Cap - Exposed!" will be helpful in gaining a better understanding of some of the forces at work here.)

One of the theories is that huge sheets of ice developed on the top of the mesa and as they got thicker and thicker, they flowed over the edges which thinned those areas of ice down leaving the center much thicker than the edges with the sheer extra center weight then pushing down and outward - gouging out holes in the top and leaving behind very shallow lakes on the mesa top. Classic "end moraines" are barely discernible (if at all) as even if there were glaciers on top, the materials gouged out would have been carried over the edge of the mesa scarp.

What about down here on the lower benches surrounding the flanks of the mesa top? Is there evidence of glacial activity?

When you arrive at GZ you will be walking facing South and looking down a shallow drainage area. Look to both your left and right. You will see large boulder piles to both sides of you. These boulders are basalt, having broken off of the edge of the Grand Mesa scarp above and behind you (North) in a process called "Mass Wasting" - undercutting of the supporting base materials, freeze/thaw cracking them up and eventually tumbling down around the base of the scarp. (So how did they get here?)

A. Were these boulder piles formerly connected? Were they once a part of a ridge (created by Slump Block Failure as discussed in the nearby Earthcache "Big Picture") and you are in the "back-slope" area that tilted toward the Mesa Top scarp face behind you? Did this ridge then trap a glacier which ultimately "PUSHED" the ridge down slope, dumping the rubble over the edge further below?

B. OR - Do you think (as some do) that there was never any significant glacial activity on Grand Mesa and this "opening" was created simply by water erosion (and ice in the winter!) which eroded under and around while pushed these massive boulder down course and over the edge? If so, where did the massive amounts of water come from that would be capable of moving boulders this size? Realize that the top of the Mesa is right behind you with only a minor shallow collection area and water way coming through here. (was it glacial melt from above?) Also note that there are no significant boulder fields scattered about between you and the base of the scarp.

C. ALTERNATIVELY - Rather than having pushed "through" a ridge that may have been here, did glacial ice gather these boulders from above and push them into the piles you see? (creating a classic "Lateral (side) Moraine") while the frontal area of the glacier continued on down slope and over the next edge/step down? (See "Grand View Cairn" for a view of that next edge/step down)

YOU DECIDE! We will keep tabs of the poll results and forward them for input to the ranger station.

You may log your find immediately AND MUST POST YOUR DECISION IN YOUR LOG (using the letter of your choice ( A, B, C - or D?) as to the questions posed above using one of the following choices:
(along with any supporting logic you may wish to provide.)

A. Glacial ICE pushed through what was formerly a ridge
B. Water (and Ice) eroded and pushed through what was formerly a ridge
C. Glacial ICE brought boulders from higher up and deposited them in these piles
D. Yet another alternative? - in which case you MUST defend your reasoning in your web log!
I have actually done this, disagreed with all the given options in an earthcache & defended my position!
You are welcome to do so here! There are no "wrong" answers, only opinions.

TO COMPLETE THE PROCESS - you must answer the following questions and e-mail them at the same time to TEAM kekj . Please do not post these answers in your log: It will be deleted!

1. Describe the width between the base of the two rock piles and what you believe caused this "space".
2. Describe the size of the boulders in the rock piles and what process created them.
3. Describe where they initially came from and how you believe they got here.

We would like to acknowledge the support of the rangers at Grand Mesa Visitor Center, in particular, resident geologist Mike Wiley, for having provided help, comments, and review in setting this Earthcache. Without it we would never have discovered or understood much of what Grand Mesa geology is all about!

CONGRATS to CB_Beauty and Soldier Grrrl for Co-FTF on 8-4-15!

Additional Waypoints

P15DHR0 - parking
N 39° 01.719 W 108° 01.309

09/27/2018 By BG2015
I am going with a variation of option A. This location is clearly along the scarp edge of the original massive basalt flow. It appears that a very localized slump failure created the small valley and subsequent erosion and water pushed rocks over the edge into the pile that can be seen further below and even more clearly in the topography. These piles were once part of the same ridge and have had their middle torn out. Very interesting location, especially the huge sinks in the area full of boulders. Thanks.

07/27/2018 By RollingRedHead
I'm going to go with choice B for this one. Cool spot, my kids had fun climbing on the rocks.

09/04/2017 By Lynnsdestiny1
TFTC

08/16/2017 By EcoXplorers
Fun day on the Mesa! Took a little hike and located this Cache.

09/20/2016 By GeologyJohn
I spent a fair amount of time at GZ going over the different scenarios. I think my answer is a modified version of option B; I don't think there were glaciers here, but the rock piles are due to slump block evolution. There were a number of rock piles that I walked past on the way back to the parking lot. Thanks for the earthcache that makes you think.

07/02/2016 By kekj
Visiting bugs to while checking and doing maintenance on our IACG series (and other FAVs) in and around Grand Mesa National Forest.

After being away from home GZ for 7 months AND a harsh winter on top of Grand Mesa (10’+ is normal) we had a need to do maintenance of 6-8 or our near 40 caches planted in or near the National Forest area. Additionally, the Forest Service was having a special presentation on trees, tree growth, tree cookies (slices showing rings) etc. so we decided to make an afternoon of it. We replaced 4 missing caches, several logs, and checked on several others that were questionable due to recent DNFs as well as “accidentally” planting one new one!. We are dragging a passel of TBs with us from our recent trip from Virginia so are visiting them to any of our caches that we passed by even if we did not stop to look at it as logs show recent finds. If a specific not is not made, the cache is assumed good, those that were checked and/or replaced will be noted. We also traded a couple of bugs and checked on some of our FAVs of friends while in the area. Have fun finding our caches and/or watching your bugs travels! Team kekj