Despite the steepness of the landscape, the Sherpa people found flat spaces to settle when they arrived in the Khumbu region. They located their settlements on flat areas at the bottom of glacial or river valleys, or on flat terraces that indent slopes above the valleys. The terraces are surfaces that were formed at lower elevations by river erosion. The Himalayan range is still rising because India and Asia continue to collide. As the land keeps rising up, the rivers keep cutting down. So, while rivers are cutting a new valley, the older valleys are getting uplifted to high elevations and their remnants are left as isolated pieces hanging on the sides of the valleys. The Sherpa people initially settled in Lukla and then migrated to higher elevations as the glaciers melted. (Glaciers have been melting worldwide since the Last Glacial Maximum about 18,000 years ago.)
Ama Dablam’s beauty is a function of her elegant shape and also the white rock she is made of. (I can’t resist anthropomorphizing the mountain, given her name and beauty!) This white rock is called leucogranite (leuco=white). Most granite on Earth is formed in subduction zones, where ocean crust descends beneath continental crust. This causes deep rock to melt and rise upward in the crust to form large magma bodies that cool to become granite. (Some of the magma typically continues to the surface and erupts as volcanoes.)
The Himalayan leucogranite, in contrast, forms because the colliding plates caused pre-existing continental crustal rocks to get buried deeply enough that the more siliceous components of the rocks melted and then migrated through the rock that didn’t melt. The melt eventually cooled as small granitic bodies or as veins (see rock images below).
From Pangboche, we continued uphill to the settlements of Dingboche and Chhukhung, located at the north end of the valley. This northward view is over Dingboche toward some of the highest peaks in the world. The striped peak on the left is Lhotse, the fourth highest mountain at 8,516 m (27,940 ft). Lhotse means “south peak” because of its relationship to Mt. Everest, which is obscured behind Lhotse because it is so close. The snowy peak in the distance (center of photo) is Makalu, the fifth highest mountain at 8,485 m (27,838 ft). It straddles the border between Nepal and Tibet.
Perhaps the most astonishing aspect of these mountains is their scale. The low black peaks just in front of the Lhotse ridge appear to be small hills, but they have elevations >5550 m (>18,000 ft)! We hiked to the top of Chhukhung Ri (Ri=peak) at 5565 m (18,250 ft). Yet the adjacent >8000-m peaks were still towering ~3000 m (~10,000 ft) above us!We were surprised at the size of the Chhukhung “resort”, since all building supplies must be carried up foot paths to this location at 4750 m (15,580 ft). The lodge even had one hot shower that was available for a cost of ~$7/person (gas to power it must also be carried up these paths). The ridge behind the lodge is a lateral moraine formed of loose rock pieces that were ground up by the Imja glacier and deposited along the sides of the valley when the glacier filled it. The loose rocks in the foreground were also dropped by the glacier, which has been retreating farther up the valley.On our way to the top of Chhunkung Ri (day 10), we got a closer view of the black “hills” (>5500 m / 18,000 ft!) in front of Lhotse. These rocks originated as sediments deposited in an ancient ocean hundreds of millions years ago. They were subsequently metamorphosed in the collision that has created the Himalayas, but they still show some of their original sedimentary layering. Their black color suggests the sediments were deposited in an ocean basin that was deficient in oxygen so that organic matter did not decompose. That’s Lhotse in the background. We would see Nuptse (to the left of Lhotse) when we reached the summit.Here are 4 fellow trekkers and our guide Lhakpa (orange jacket) at the summit of Chhukhung Ri. Because of the difficulty and the stellar views, we were super excited to have reached this summit at 5565 m (18,250 ft). The peak behind our group is Nuptse, meaning “west peak” because, like Lhotse, it’s connected to Everest. At 7,861 m (25,791 ft), it does not qualify as one of Earth’s highest peaks but it is magnificent nevertheless. Note the light-colored rock on Nuptse. You guessed it—that’s leucogranite. I’ll include a photo in the next post where you can see the relationship between the granite and the surrounding rock more clearly.I had to include this photo of Jay and I looking at rocks, which we did a lot! Although neither of us is a metamorphic geologist, we were impressed by the variety and beauty of these rocks that have an extended, and tortuous, history. This view is from the slope of Chhukhung Ri looking southeast across the Imja Glacier. A tributary glacier is flowing into the main valley from the ridge on the other side of the valley. This knife-edge ridge is an arête that was carved to its skinny shape by glacial erosion on both sides. That’s Ama Dablam at the right edge of the photo. Because this view is parallel to her “wings”, she appears to be just one peak. Photo courtesy of Rebecca Douglass, fellow trekker.Here are examples of pretty rocks we saw near Chhukhung. The left side is gneiss or migmatite. The swirling layers indicate the rock was buried deeply. The high temperatures at depth made the rock soft enough to flow, and some parts may have melted. The right side is schist, a metamorphic rock that started life as a sedimentary mudstone. Schist contains lots of mica, which gives the rock a brilliant sheen. The small veins were formed when molten rock intruded into the schist.I’ll end this post with a sunset view from our lodge in Dingboche, looking back down the valley toward Namche and the mountains beyond. On day 11, we walked back down the valley and then uphill again to Everest Base Camp. Stay tuned!
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