Wednesday, November 21, 2007

Beautiful Beacon Valley

On Monday, we were lucky enough to take a field trip to the Dry Valley Specially Managed Area. We went in a helo up the Ferrar Valley, and were dropped at the head of Beacon Valley for a four hour wander, and were taken out again along the length of Taylor Valley, stopping for another chunk of time at the mouth of the valley by the Commonwealth glacier and stream. We had fairly mild to good conditions but before our helo could come pick us up and bring us home, McMurdo weathered in and we had to stay out overnight. Rather than break out our survival packs and make camp where we were, we hiked three miles to New Harbor field camp at the shore of McMurdo Sound where we had propane heaters, cots and blankets and an outhouse. We were picked up the next afternoon from our very cushy "survival" spot, no problem.

Beacon Valley is special for many reasons. One is the sheer distance to get to it, further than most of the commonly or easily visited Dry Valleys like Taylor or Wright. It is a wonderful place to see a large amount of Beacon supergroup sedimentary rock (around 400-230 million years old) and get up close to it. The Beacon supergroup is a very deep/thick series of sand and silt stone sediments deposited by water and later uplifted. I scrambled up a scree slope of eroded material to get to the steep cliffs of rocky outcropping and to a vertical section of dark Ferrar Dolorite (an igneous intrusion from around 180mya).

After getting a closer look at the large chunks that had fallen off the crumbly looking rock, I decided against going right up to the wall and touching the rocks. I got as high as I could on the unstable slope and sat to look out at the valley for awhile. I could hear the wind whistling past the irregular surface of the huge rock face, and nothing else. Really lovely after the hustle and bustle of McMurdo's 24/7 transportation hub noise. I couldn't sit too long, keeping moving there was important as it was chilly and windy even though the sun was partially out.

Another Dry Valley feature that is a little different in Beacon was more easily seen from the helo, the huge frost polygons on the valley floor, hard to recognize them on the ground, even when we were standing on them. Other areas we saw polygons had smaller ones. The ice underneath the polygons here in Beacon Valley is thought to be some of the oldest ice in the world somewhere between 7-14 million years old, scientists are sampling it to get ancient atmosphere.

Everyones attention was definitely attracted by the extreme wind weathering in action visible on every rock in the area to some degree. Many of the finely grained rocks have a satiny smooth texture and rounded edges that comes from being sandblasted by airborne sediment in the wind. There were pockets of this blasting material in the lee of most large rocks. Other rocks have been sculpted into strange, sinuous shapes by the same action, their softer areas being more vulnerable to abrasion.

What do you notice about the rocks from the Beacon Valley floor in this picture?

No comments: