Thunder Mountain Lakes Blew My Mind

Note to the reader – this blog post describes a trip to fragile ecosystem via a risky trail. If you decide to follow me here, please use caution and turn up your leave-no-trace skills to 11. 🙂

The third time really is the charm. In June I tried to make it here but the road was still snowed in. In early July I started from a different lower-elevation trailhead, but the pass was…. still snowed in. The snow finally melted in early August – success!

I finally completed this truly magical backpacking trip.

I started from the Hope Lake Trailhead up Tunnel Creek Road off of Highway 2, just a few miles west of Steven’s pass. The Hope Lake trail heads uphill to connect with the Pacific Crest Trail, where I turned south. There’s a rockfall just south of Hope Lake that has a booming and adorable small mammal population – I saw 2 families of marmots and a family of pikas! After the steep first 2.5 miles of the hike the trail flattens out, the trees open up, and all of a sudden you expect Julie Andrews to pop out and start singing the Sound of Music.

The hike from here to Trap Lake is a delightful ramble through wildflower meadows and groves of pine trees.

I got to Trap Lake around noon, claimed a campsite, and made ramen for lunch. And then I started to climb. To get to Thunder Mountain Lakes you head up the PCT to Trap Pass, and then turn south onto a seriously sketchy trail that follows the county line south and up to Thunder Mountain Ridge. Sketchy as in if you slip, you fall 500 feet. Not for the faint of heart, and it could be risky for dogs.

The trail takes you up above the snow line, and starts to be marked with cairns to guide hikers through the snow field and bare granite. There are a few islands of vegetation, including stunted pine trees, pink heather, and blue dwarf lupine. The bees were going wild on the heather – I guess they only have a short window for foraging up here.

At this point I was 6.5 miles from the trailhead and 3,300 feet higher up in elevation. Just as I was having to start counting my paces to keep myself going, I turned a corner and my jaw dropped.

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I had made it to Thunder Mountain Lakes! I could see all the way to Mt. Daniel and Hinman Glacier in the distance.

I hiked down to the lake and sprawled on the nice warm granite to eat a chocolate bar. As I got up to look down at the lower lake, I heard a rustle….

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… and there was a mountain goat with her fuzzy baby! They’re such lucky creatures, getting to live here full-time. I hung out with them until they made their way along the ridge. The baby kept trying to sprint up onto rocks only to fall – luckily straight into its mom. It takes true love to be your offspring’s bouldering mat.

I lingered up by the lakes until the sun started to sink close to the ridgetop. The nice thing about hiking downhill is that it leaves me with more energy to spare to admire the rocks. The downside of admiring the rocks is that I get distracted and loose the trail. But these rocks were great!

They’re all granite, but conceal a subtle story. Textbook illustrations often depict magma bodies as single lumps that rise and cool neatly independently. Reality, as always, is more messy. Magma bodies (or batholiths, as they’re referred to once they cool down) in reality can merge, or pick up bits of other batholiths, or be reworked once they’ve cooled.

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For example, this photo (above) shows a light gray batholith that cracked under pressure once it had cooled. A different kind of magma forced its way through the cracks as it rose, forming the dark grey stripe. Later the line of weakness was reopened and filled with hydrothermal quartz, creating the white streak. It’s kind of like a turducken of igneous rock.

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And in this photo, the dark grey magma body ripped up chunks of a paler batholith as it rose and incorporated them into its mix, Pac Man style.

As I headed north back to Trap Pass I got phenomenal views of Glacier Peak as well as glimpses of Mt. Baker to the northwest.

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Heading downhill back to my camp I met several fat marmots. Two of them were engaged in a clumsy but effective high-speed chase and high-volume screaming match. Their counterpart above Trap Lake obviously don’t think much of humans and screamed at me to let me know it. (lower left photo)

Trap lake was an idyllic place to spend the night, especially on a Sunday night when most of the weekend backpackers were long gone. I really got a prime campsite (above right) and enjoyed the luxurious packable chair that my sister (the one featured in all the Twin Trek posts on this blog) gave me for our birthday. Glamping all the way!

I spent a leisurely Monday in camp and then headed back to the trailhead at an equally leisurely pace. I really didn’t want to leave. Between snack, scenery, lunch, and pika -appreciation breaks I managed to stretch the 5 miles into 6.5 hours.

I may have had to drive back to civilization that day, but I’m definitely coming back here!

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Rampart Ridge Rocks!

At Vanderbilt University’s Wilderness Skills club we classified adventure into two types of fun. Type 1 fun was fun to experience and fun to remember. Type 2, the slightly more common type, was miserable while it happened but either has a great reward or created a story that got you attention at parties.

The hike up to Rachel Lake after work with a 30-pound pack on my back was decidedly Type 2.

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Where in the world was I? Trailhead marked in blue, trail in dark green. map created in ArcMap by C. van Stolk using trail shapefiles created by the US Forest Service and ESRI’s Streets basemap.

Rampart Ridge trail map

Trail in bright green – map created in ArcMap by C. van Stolk using trail shapefiles created by the US Forest Service and ESRI’s terrain basemap.

I got off work early on that Friday, headed east on I-90, turned off at the exit for Kachess Lake, bounced up potholed gravel roads to the trailhead, and set out for adventure. I knew the hike went from 2,800 to 4,800 feet in four and a half miles. What I had foolishly overlooked is that it gains 1,400 feet in the last 1.2 miles. A significant distance of that 1.2 miles is literally in a creek bed. It had me questioning my life choices. I had planned to go all the way up to Rampart Lakes at 5,100 feet but I was absolutely done by the time I got to Rachel Lake. I was too cranky to eat my ramen noodles. I set up my tent at the outskirts of an inordinately crowded back country campground just as it got dark, made a cup of tea, and turned in for the night.

The next day was 100% heavenly Type 1 Fun.

I left the burden of my camping stuff where it lay and headed uphill into a clear blue day. My goal was Alta Peak at the northern end of Rampart Ridge, elevation 6,152 feet. I climbed up the ridge past fields of glacier lilies and heather and creeping phlox. It took me about two hours to make it to the top, with views of Mt. Rainier, Mt. Adams, and Glacier Peak. I settled in for an hour with my chair and my map to plan further adventures while I could see so much of the landscape!

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Alta Peak, looking south at Mt. Rainier (center) and the Summit at Snoqualmie ski routes (center right).

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Alta Peak, looking north (the white tip of Glacier Peak is peeking out from behind the Four Brothers on the center right)

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Looking down past the snowdrifts to the basin below Alta Peak

I then rambled downhill to have lunch at Lila Lake. It was hopping with backpackers but I found a nice spot to eat my snack assortment and get yelled at by a marmot.

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Once I had my fill of exploring the bouldery outcrops at Lila Lake, I headed south to Rampart Lakes. I spent the rest of the afternoon basking on a rock with a view at the Rampart Lake furthest along the trail. I braved the water for a swim and dried off in the sun while reading a mystery novel and enjoying my sippy flask of rosé. I did not join the hikers who were penguin-sliding down the snowdrift straight into the lake, though.

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Rampart Lake, looking up at Rampart Ridge.

Around 6pm I headed back down to Rachel Lake to cook dinner and explore the campsite possibilities in the main campground for next time. I went to sleep in an exponentially better mood than I had the previous night.

Sunday morning I hoped to make it down the horribly steep creek bed part of the trail before the day hikers would be heading up it. Mission successful! I took loads of photos of wildflowers. I set up to finish my novel and eat lunch at a rocky waterfall overlook about a mile from the trailhead.

By this point Friday’s uphill slog was completely a thing of the past. All things considered, the trip had been a delight.

But wait! I couldn’t ignore the cool rocks. You know me.

The rocks exposed up at Rampart Ridge were gray with white clusters of larger elongated crystals. I thought they were really distinctive, but didn’t know their name.

It turns out these rocks have the epic moniker of “glomeroporphyritic basalt”. Glomeroporphyritic translates out of science Latin into “collected-together larger crystals”. In geology-ese, “porphyritic” refers to an igneous rock texture where larger crystals are set in a matrix of rock crystals with a much finer texture, like blueberries in a muffin.

Porphyritic igneous rocks form in two stages – the first one at deep in the earth’s crust, and the second in a shallower, cooler zone at or near the earth’s surface. The large white crystals in Rampart Ridge’s basalt formed when the magma was deep underground. They had plenty of time to slowly cool into large crystals in the hot environment at depth. However, some igneous or tectonic process suddenly shoved the magma body up towards the surface. This made the rest of the magma cool suddenly. Because these newer crystals did not have time to grow, they stayed very small.

But why did this one white mineral form crystals at depth, and not the others?  I turn to a familiar chart from my geology textbooks for the answer. It’s called Bowen’s Reaction Series, and describes the order in which minerals crystallize out of molten rock. This series springs from painstaking experiments involving pulverized minerals, a very very hot oven, and more patience than I possess. They revealed that minerals form into crystals at the different temperatures along a gradient.

The elemental mix of magma that becomes basalt creates the white mineral calcium plagioclase and the dark gray/black mineral pyroxene, with only trace amounts of other minerals. Calcium feldspar has a higher melting temperature, and so solidifies at a higher temperature while pyroxene has not yet formed into crystals. An important caveat is that not all magma contains all the elements necessary to make every rock in the series, so several minerals may be “skipped” in a certain magma body.

For example, quartz has the lowest melting temperature of all the common minerals, which is why it often forms decorative crystals or veins in the voids left when other minerals have already crystallized.

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Quartz veins in volcanic rock higher up on Alta Peak.

The two kinds of rock I saw on this hike date mainly from the Eocene and Oligocene time periods between 55.8 and 23 million years ago. Washington was roughly at it’s current location on the globe back then and the volcanoes of the Cascades were starting to rev up. Since then, these rocks have been folded by tectonic forces, broken by faults, and eroded until they cropped out in the patchwork patterns that geologists map today.

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Summarized in MS Paint from the original Snoqualmie Quadrangle Geologic Map by Tabor, Frizzell, Booth, and Waitt of the USGS: https://pubs.usgs.gov/imap/i2538/

The glomeroporphyritic basalt dates from the late Eocene period. It’s colored medium green and marked as Tnbg on the map above.

Tv and the light pink color stands for Oligocene volcanic rocks – an igneous jumble that’s a few million years younger than the glomeroporphyritic basalt. The rocks on Alta Peak are describe in the USGS pamphlet for the Snoqualmie quadrangle as “coarse volcanic breccia and tuff with minor ash flow tuff). They look almost like concrete made with blocky, angular aggregate. Breccia describes rocks created when magma shattered and engulfed surrounding rock as it erupted. Tuff forms when ash becomes cemented by its own heat, like how I described in the Smith Rocks post from 2018. Breccia makes up the ridgeline of the photo below – you can really see how this one rock classification encompasses a bunch of different kinds of rocks that erode differently to create a mix of straight ridge lines and messy talus slopes.

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It’s hard to get a sense of the scale of the waterfall in the center from the photo. I could hear it roaring down the rocks from a quarter mile away!

I’m still doing research about how these rock types ended up juxtaposed. Western Washington’s rocks tell a complex story of bits of foreign continents (called accreted terranes) that were stuck onto the rest of North America by subducting plates, then covered with volcanic rocks and shuffled around by faults. It’s the northern relative to the process in Southern Oregon that I wrote about in my accreted terranes post. Up here, the terranes were even more altered by volcanism and faulting.

It definitely created a fantastic landscape!

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Volcanic breccia on Alta Peak

Resources:

Definition of glomeroporphyritic basalt: https://blogs.agu.org/georneys/2011/07/14/geology-word-of-the-week-g-is-for-glomeroporphyritic/

USGS map and pamphlet for the Snoqualmie Quadrangle: https://pubs.usgs.gov/imap/i2538/

Info on volcanic breccia: https://en.wikipedia.org/wiki/Breccia#Volcanic

Information on Bowen’s reaction series: https://courses.lumenlearning.com/physicalgeology/chapter/3-3-crystallization-of-magma/