[Scrooge]

................................. TECHNICAL REPORT ................................. Crevassing and breakdown in Big Four's Rucker Ice Mass

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When I started my ramble around Big Four's Avalanche Cone, I only intended to go about halfway up the left hand side, to see if I could get a look into the Belfry, that mysterious area at the top of the Cathedral Room where Rucker Falls cuts back under the ice to form the Ice Caves. From the bottom, it looked like the crevasses and breakdown in that area might provide a route and a platform that would make such viewing possible.

Big Four Avalanche Cone left 11-04-09 annotated

Breakdown in left moat 11-04-09

End of left crevasses and bottom of Belfry 11-04-09

Fracture lines 11-04-09

It looked like there were an unusual number of cracks and crevasses in the ice, which was interesting in its own right. The kinds of crevasses that form, and where they form, is one of the elements that could help us decide whether Big Four is a real glacier ........ or just a big pile of ice.

Budding crack - left 11-04-09

Tracking the crack 11-04-09

Crack & crevasse merge 11-04-09

Crevasse 1 11-04-09

I started up the avalanche cone following a crack that did not parallel the curve of the lefthand moat, but rather, appeared to diagonal straight up across the ice. However, the crack became a crevasse and the crevasse curved back around to intersect the moat. It was a typical, scalloping crevasse, the kind that form along the side of any ice mass when the support melts out from under them above a slanting wall. ........ The second crevasse I followed did turn out to have one surprising historical parallel.

January 2003

November 2009

When I climbed the glacier, in January 2003, I followed an almost identical crevasse till it intersected the moat ........ and till I could stick my ice axe handle through the bottom into the void beneath. I took some trouble, that time, to see that the section of ice I was on was actually cantilevered above the wall of the cliff. Last week, I followed the ridge of ice to the left of the first crevasse, hoping it would take me far enough to see into the Belfry, but it didn't, so I backtracked and crossed over to that second crevasse.

View down left crevasses 11-04-09

Second crevasse continued 11-04-09

Sigh 11-04-09

Grrrrr! ....... 11-04-09

It didn't go far enough, either. Even if I'd been willing to take a couple of 2 foot steps to the top of knife-edge ridges, there still was a section of ice, invisible from below, that I couldn't have seen around. .......... But I did find one curiosity, a thin, gray line running through the ice in a direction unrelated to any of the modern surfaces and cracks. ......... Any ideas?

What's my line? 11-04-09

What's my line? 11-04-09

Having drawn a blank on the Belfry (for the time being), I decided to cross the avalanche cone and take a look at the crevasses on the righthand side. I'd noticed them coming in, a series of crevasses, more or less paralleling the righthand wall, but appearing progressively further from the wall. It got me to thinking.

Big Four avalanche cone from the right, emphasizing the crevassing and breakdown. 11-04-09

The remains of the Rucker "Glacier" in September 2005, showing the extensive talus slope along the base of the west cliff.

Right crevasses 11-04-09

Ice Caves detail September 2005

One of the problems with calling the Rucker Ice Mass a glacier is that there is no apparent forward motion. As far as I can see, there's no trace of a terminal moraine, or of any of the seracs or broken sections of ice that we usually associate with the forward edge of a glacier. Perhaps that's not surprising, since the AC sits on a nearly flat base. Since sliding is not "encouraged", the ice just piles up, and slides down the surface of its own slope. However, when I first saw the righthand series of crevasses, extending in parallel arcs more than 100 feet out from the wall, I began to wonder if there might not be some sort of unexpected glacial movement taking place along a vector perpendicular to the west wall. ........ Then I thought to look at those 2005 pictures again. Just as they'd showed me the course of Rucker Falls, so now they revealed the surfaces normally covered by ice and snow. It turns out that there is a very extensive talus slope along the base of the wall, nearly 100 feet high, and extending out even further than usual from the base of the wall. Thus, the layer of ice where those righthand crevasses have formed is relatively thin. The whole layer is undermined by melting, so all the crevasses are in fact typical scallops and are not indicative of any other kind of movement. Since I didn't figure that out while I was on the ice, I decided to turn back up towards the top, to see what else I could learn.

Right crevasses 11-04-09

Right crevasses from above 11-04-09

Upper right moat 11-04-09

Iceclimber November 2002 - upper right moat

The big wedge of breakdown in the righthand moat is fairly typical. Back in November 2002 it was connected to the main body of ice by a fairly good ramp, so I was able to walk out on it to take that picture of the solo iceclimber. (That's the picture I was looking for, Jim). The tip of the avalanche cone develops with great similarity from one month to the next, and one year to the next.

Ice Girl 07-25-07

Tip of Avalanche Cone 11-18-08

Tip of avalanche cone 09-15-09

Big chicken 09-16-08

AC topknot NOT 10-06-09. Note that the top blocks of ice are just barely connected to the main mass.

And they didn't make it. AC tip and upper right moat 11-04-09.

But the "tip" is really just the edge of a much more important feature, the "topknot". How and why the topknot forms turns out to be of great significance in evaluating Big Four's glacial status.

Topknot tele 07-08-08

Topknot 08-08-08

Topknot detail 08-12-08

Big Four topknot 07-03-07

AC tip 07-10-09

Topknot pan 08-12-08

I've been intrigued by the topknot, ever since I first started noticing it, perched at the tip of the Avalanche Cone, 300-odd feet above the valley floor, clearly separate from the main body of the ice. ........ It's a big block of ice, 60 or 80 feet wide, 30 or 40 or 50 feet thick from front to back, and at least as thick from top to bottom. ........ It isn't there at the beginning of the season.

Avalanche cone 05-27-09

AC top, no knot 05-27-09

And it isn't there at the end of the season, either.

08-14-07 Looking over the AC top at a column, last remnant of the topknot, with a usually hidden section of Rucker Falls in view.

Topknot remnant 11-18-08

It's the dissolution of the topknot that gave me the key to its creation. ........ During the winter, while storms and avalanches build up the pile of snow and ice at the base of the Big Four cliff, Rucker Falls is frozen or inactive. In the spring, when meltwater turns Rucker Falls into a torrent, the relatively warm water and the accompanying stream of warm air disappear down the cliff behind the ice. And the ice starts melting, opening a bigger and bigger void behind and underneath the upper section of the avalanche cone. The immense weight of that unsupported block of ice causes a fracture to form along it's front edge, a crevasse, and the block tips back against the cliff, separate from the main mass.

Crevasse pan 08-12-08

AC crevasse 06-27-09

AC crevasse right 06-27-09

Of course, the actual process is much more complex and varied than that simple outline would suggest. The crevasse is not a nice, straight cut; the melting of the back and underside of the block does not progress on any sort of regular basis; and the face of the cliff is rough and irregular. However, what does seem to happen with regularity is that the block "hangs up", supported in some fashion by contact with the cliff and the wall of ice in front of it ........ while the main body of the avalanche cone shrinks, partly by ablation, partly by compaction under the force of its own weight. ........ Incidentally, that compaction, where the ice condenses, deforms, and "flows", may be the one truly glacial characteristic of the ice at Big Four.

Lefthand end of righthand crevasse 11-04-09

Bitter end 11-04-09

View down into righthand crevasse 11-04-09

Righthand end of upper crevasse 11-04-09

Righthand end detail 11-04-09

Sometimes the crevasse at the front of the topknot is a mess, filled with a mass of breakdown.

Beginning of lefthand crevasse 11-04-09

Lefthand crevasse 11-04-09

Lefthand crevasse 11-04-09

Lefthand crevasse 11-04-09

Lefthand crevasse 11-04-09

Lefthand crevasse 06-27-09

Lefthand crevasse 11-04-09

Lefthand crevasse 06-27-09

Sometimes it's nice and smooth, and as sharp as if it had been cut with a knife. >>>>> But it isn't always the same crevasse! Oh, at any given point in time it is. Those righthand end an lefthand end pictures taken November 4th are all the same crevasse. But, in spite of some similarity in appearance, those photographs taken in June and November are not the same crevasse, at all. The crevasse in the June photograph was located about a hundred feet higher and a hundred feet further back than the crevasse photographed in November. The avalanche cone has shrunk dramatically. The original topknot has collapsed and disintegrated. A new one has formed (or probably a series of new ones - see those "remnant" pictures above). And the process continues, as we shall see as we return to the Belfry. But first, a digression, to remind you of what the Belfry is. That requires a trip to the back of the Ice Cave, and a look at Rucker Falls coming down the back wall.

Ice Cave waterfall 09-25-07

Lower Rucker Falls.10-06-09

Cathedral Room steeple and belfry 10-06-09

Belfry 10-06-09

I said in my previous report on the Ice Cave that I was puzzled by the fact that the rear entrance to the cave appeared to be on the side of the avalanche cone, rather than at the top. I resolved that when I found the 2005 pic that showed the whole course of the falls.

Avalanche Cone left 11-04-09b annotated

Ice Cave and Rucker Falls 09-04-05 annotated

Since I didn't get my look into the Belfry when I tried from the bottom, I decided to try from the top.

Looking down on the Belfry roof 11-04-09

Belfry detail 11-04-09

Belfry ceiling and Avalanche Cone tip 09-02-07

Standing on Belfry roof 11-04-09

I guess this is my contribution to the "FEAR" thread. Imagine me standing out on that middle projection in the second picture, trying to convince myself to lean over just a little further so I can see down into the cave ......... while I'm remembering that breakdown up above. Sigh. I am still here. Incidentally, there are a couple of reasons that the Belfry stays open the way it does. First, Rucker Falls is flowing down that section of cliff. Any ice that falls is quickly broken up and carried away by the stream, so there's no breakdown left clogging the moat. Second, the stream of warm air that accompanies the falls increases the rate of melting in that area, so you get those hollowed out spaces along the edge of the AC and continuing on down into the Ice Cave, itself. Anyway, while I was on my way down the try to see the Belfry, I found one more set of crevasses.

Transverse crevasses 11-04-09

Transverse crevasses ending above the Belfry 11-04-09

A pair of transverse crevasses, which, on the Big Four Avalanche Cone usually form only at the front of the topknot. Given the condition of the current topknot, perhaps this is a new topknot in the making. Or perhaps it's something more dramatic. These crevasses end at the Belfry. Which means that if they continue to open, they'll destroy the ceiling of the Cathedral Room. Breakdown will fill the Cathedral Room and the back of the Ice Cave. After this winter's cycle of storm and avalanche rebuilds the Avalanche Cone, a new cycle of cave formation will begin. ......... The new cave will seem quite familiar.

[peltoms]

Nice work you are addicted-a crevassehead. The crevasses indicate a differential movement. Usually this is down glacier. however, in this case the diminishing slope and thickness down glacier do not encourage motion. In this case it appears the crevasse opens due to the moat near the rock, little support for a thick wedge of snow and ice, which tends to try and fall toward the rock, but is held in check by its thickness.

[Redwic]

WOW!!! This was one of the most enjoyable reads I have had on NWH in quite some time. Well-thought out, and I have even more respect for Scrooge now. GREAT JOB!!!

[El Puma]

Very, very interesting, Scrooge! Forwarded this to my dad who worked at UW Glaciology in the 50's and did much of the surveying and movement studies on the Nisqually...

[Trail snail]

I have never been a climber (sigh) but that was fascinating for me to read, and along with the pictures. I have always stood at the bottom gazing UP at all of that, wondering and wishing I could see it. Thank you.