A Moment of Volcanic Clarity: Rainier and St. Helens Show Themselves

I'm up in the Pacific Northwest for family things (it's the holidays after all), but I've been on the hunt for Cascades volcanoes during our journeys from one place to another. True to Pacific Northwest form, the weather hasn't cooperated. We drove north through Portland and Seattle a few days ago through scattered rainstorms, and when the time came to drive south again, an inversion layer set in and fog was everywhere. But we had one moment of clarity. As we came over a rise near Napavine, we broke out over the inversion layer, and had a moment to see Mt. Rainier.

Rainier is a huge mountain. It is 14,410 feet tall (4,392m), and is covered by 156 billion cubic feet of glacial ice. With its location so close to large population centers, it is one of the more dangerous of the Cascades volcanoes, although it hasn't been active in historical time. The last eruption was around 1,000 years ago. But a number of towns are built on mudflow deposits (lahars) from Rainier, highlighting the hazardous nature of the volcano.

We drove back into the fog for a few more miles, and took a chance and headed east from Castle Rock to see if anymore volcanoes would be visible. At Silver Lake about 5 miles in, the clouds cleared and we were blessed with a stunning view of Mt. St. Helens. There is a multi-agency visitor center at the lake, and a nice nature walk that extends out into the lake on a small levee and boardwalk.

Silver Lake is an interesting volcanic feature itself. The 1980 debris avalanche that precipitated the eruption of Mt. St. Helens was not the only mass wasting event that has happened in this area. The landslide in 1980 dammed several side canyons, creating several lakes, most notably Coldwater Lake.

2,500 years ago, a similar event took place, and several lakes were formed near the volcano. When one of the lakes overflowed and failed catastrophically, the ensuing flood carried debris downstream, blocking the drainage now covered by Silver Lake.

The lake must be a sea of green in spring and summer, but here in winter, the plants were frozen and wilted away. There wasn't much in the way of animal life present, but a blue heron was perched in a tree where it could be framed by the peak of Mt. St. Helens.

St. Helens is deceptively serene today. The debris avalanche and violent eruption of 1980 are justly famous, and explosions continued through 1986. The mountain reawakened in 2004, and erupted quietly for four years, building a second volcanic dome in the crater of the mountain. The second eruption was nowhere near as famous as the first for the obvious reason: no one died.

Several good paved highways approach the mountain, and several visitor centers can be found along Highway 504 above Interstate 5 on the west side of the volcano. We had little time for exploration, but we enjoyed the walk along Silver Lake, which is only five miles east of the Interstate.

Into the Great Unknown: Visions of Paradise, and a Bug's Horror

The third day of our journey down the Colorado River began as an idyllic journey through paradise. If that seems like a set-up for a disaster at the end of the day, it isn't, unless you count the poor bug (read below). We were traveling about 12 miles from Shinumo Wash to Lower Buck Farm Camp, a stretch of river remarkably free of large rapids (Thirtysix Mile Rapid, a 4, was about it). We were well into Marble Canyon, where the river walls are dominated by the Redwall Limestone (not really marble, but the river polish makes it look like marble). To me, the day was as close as I can imagine to being an earthly paradise: full of beauty, color and serenity.

The Redwall Limestone had its origin in a sort of serenity, or maybe stability is the better word. For millions of years during the Mississippian Period, between about 360 and 323 million years ago, a shallow tropical sea spread and regressed across the continental interior. The tropical waters were filled with life, including crinoids (sea lilies), brachiopods, bryozoans, clams, snails, fish, sharks, and even a few trilobites. It accumulated to depths of 400 to 800 feet, and the hard limestone forms one of the most prominent cliffs in the Grand Canyon (the location of practically every trail in Grand Canyon is determined by where it can cross the Redwall).

Limestone dissolves in mildly acidic water, so caverns will form readily in the Redwall. A vast network of caves are present throughout the Redwall, and many open out into the cliffs above the river. Being an armchair spelunker, I wanted to get out and find a way to explore every cave we saw in the cliffs above. Most were clearly inaccessible, but the cave in the photo above could be reached by humans. It was used by Robert Brewster Stanton in 1889 to stow some of their gear as they abandoned their tragic journey down the river after their leader (and bankroller) and two others drowned. It is called Stanton's Cave to this day.

It turns out, though, that humans have used the cave for a long time. 3,000 to 4,000 years ago, humans constructed split twig figurines, and left them in Stanton's Cave by the dozens. It is thought that 165 of these precious archaeological treasures were removed by visitors between 1934 and 1969 before the park service removed the remaining 74 during an excavation (my feelings about this looting is unmentionable in this family-rated blog).

Split twig figurines on display at Tusayan Ruins, South Rim of Grand Canyon National Park

Other creatures used the cave as well, including California Condors and Mountain Goats, whose dated remains go back 12,000 years. And remarkably, driftwood was carried into the cave during a river flood around 40,000 years ago. The cave is 160 feet above the river!

Most recently, the cave has been occupied by several species of bats, including the rare Townsends big-eared bat. The largest nesting colony known in Arizona was present here years ago, but persistent tourist incursions drove them away. Eventually a gate was constructed to allow access for the bats, but to keep people out. Apparently it has been working, and a colony has been re-established.

Just downstream of Stanton's Cave, an expected splash of greenery coated the slopes of the canyon before us. As we drew closer, we could see water bursting out of the cliffs. Water is another wonderful property of the Redwall. The caverns, fractures, and fissures provide avenues for groundwater percolating through the layers above to be concentrated near the base of the formation, and springs are a common feature at the base of Redwall Formation. Vasey's Paradise was a wondrous example of one of these springs.

We pulled out to have a closer look (for some it was an opportunity to fill their solar showers with clear spring water). We had to step carefully, because some of the greenery was composed of poison ivy!

I caught a shot of my brother enjoying a view from a large boulder along the shoreline. I carefully made my way down to join him. Carefully, because only a week before the trip I had done something to my heel and even had to use a cane for a day or two to get around. I didn't want a recurrence, and was only wearing sandals while on the river. The rock provided a nice upstream perspective of the springs.

Back on the river, we passed another Blue Heron. I couldn't resist another few pictures!

After another few bends in the river, I got a lesson in perceived scale. One can see a dark cavern at river level in the distance. As we got closer the hole got bigger...and bigger...and bigger! We had reached Redwall Cavern, one of the more extraordinary sights on an extraordinary river. John Wesley Powell remarked in 1869 that the huge declivity could hold fifty thousand people. Others later suggested more like 5,000, but in any case, it is huge. We pulled out for a little exploration.

Even before turning my camera into the cavern itself, I had to snap a shot or two of the reflections of the surrounding cliffs on the river. This was one of the calmest parts of the river so far, but Redwall Cavern must exist in part because of lateral erosion of the river during high water (the entire cave was filled with water in 1957 during a flow of 122,000 cubic feet per second; today's flow was more like 12,000 cfs).

Blocks of Redwall that had fallen into the cave contained numerous fossils. Some of our travelers pointed out the crinoids and brachiopods seen below.

I started exploring the depths of the cavern, taking the surprisingly long walk around the back of declivity. The scale is impressive, compared to the rafts of our little flotilla.

The ceiling of the cavern provides a nice frame for looking at the river.

Did I mention that the cavern is huge?

It was a fascinating place to wander, and a cool respite from the sun. I've also seen video of Redwall Cavern in an entirely different circumstance; check out this example of the cavern during an intense monsoon storm. It's awe-inspiring...

Ichnology is the study of trace fossils, the tracks, burrows and other traces of past life in the absence of shells or bone. I've seen many trackways in ancient sandstone formations, but we saw a bit of drama reflected in the sand within the depths of Redwall Cavern. A large beetle had been walking along the uneven sandy surface, and had come to grief in someone's footprint. Such dramas have been preserved in formations like the Coconino or Supai, and in the right conditions, the same could have happened here. The story has a happy ending; the beetle wasn't dead yet, and we set him upright again to continue his journey.

The day continued, but this post is already long. To be continued!

Into the Great Unknown: Whodunnit? A Mountain Range Goes Missing

The new day, our second on the grand river, began with a startling sunrise. Sunrises and sunsets in the Grand Canyon are not like other places. One never sees the sun rise above or dip below the horizon, because in the deep canyons, there is no such thing as a horizon. Like Plato's cave, we can only comprehend the sun rising over the Earth's horizon by imagining it from the reflections coming off the adjacent cliffs. If the sun hits camp at sunrise or sunset, someone has made a big miscalculation in choosing a campsite. Staying out of the sun for as long as possible is a continuing strategy during a summer rafting trip on the Colorado.

There was a foreshadowing of today's mystery in the previous post. On our continuing journey into the Great Unknown, rafting the Colorado River through the Grand Canyon, we had passed through three geological formations, the Kaibab, the Toroweap, and Coconino. The first two formed in a coastal environment, while the Coconino developed in a sand dune dominated desert. But we ended our first day on the river in the midst of the Hermit Formation, a striking red-brown layer composed of siltstone and mudstone. The bright red color in such rocks (and the presence of sedimentary structures like ripplemarks) is strongly indicative of deposition in a river floodplain environment.

As we drew deeper into the canyon, we encountered successively older rocks, and they revealed more and more redbeds. Now there were ledges and cliffs of sandstone and other coarser sediments, indicative of a higher energy environment, such as the river channels of large floodplains and desert sand dunes. Clearly a major geologic event had taken place, one that produced a vast volume of sediments over a wide region. For a region of the Earth's crust that had remained remarkably stable for nearly a billion years, this event stood out.

We had entered the Supai Gorge, named for the four formations of the Pennsylvanian-Permian aged Supai Group. Their names are tongue-twisters: the Watahomigi, Manakacha, and Wescogame formations and the Esplanade Sandstone. Where did all these sediments come from, and how do we know? The sediments had to come from a mountain range, but any such mountain ranges no longer exist, having been eroded to rubble many millions of years ago.

Ripplemarks and crossbedding in the sediments show that the rivers were flowing in a general southwest (today's southwest, anyway) direction, meaning the mountains lay to the east or northeast. In southwest Colorado, there are younger rocks, similar to the Mesozoic rocks found around Zion and Capitol Reef in southern Utah. But beneath them where the Paleozoic rocks should be found, there are only ancient Proterozoic metamorphic rocks and intruded granites. These ancient rocks are the roots of the Uncompahgre Uplift, otherwise known as the Ancestral Rocky Mountains.

The origin of the Ancestral Rockies remains somewhat of an enigma to geologists. They coincide in time with the collision of South America and Africa with the southeastern part of North America, an event that ultimately produced the supercontinent Pangea. But the Ancestral Rockies are hundreds of miles removed from the collision zone, so geologists infer a sort of chain reaction in the crust along ancient fault systems. In any case, the rise and destruction of a mountain range in Pennsylvanian and Permian time has provided us today with one of the most scenic and colorful layers in the Grand Canyon.

I came to love two bird species who make their home in the canyon. One of them was the blue heron. We would see them all through the canyon, gracefully soaring over the water, or stepping carefully in the shallows, looking for fish and other prey.

We continued to descend deeper into the canyon. Today's route would take us through a part of the canyon called the "Roaring Twenties", a series of rapids spaced on average only a half mile apart. After the relative paucity of rapids on the previous day, it was a real roller coaster. Remembering the scale of 1 to 10 for rapids in the Grand Canyon, we faced House Rock Rapid (7), North Canyon Rapid (5), Twentyone Mile Rapid (5), Twentythree Mile Rapid (4), Twentythree and One-Half Rapid (4), Georgie Rapid (6), Twentyfour and One-Half Rapid (6), Twentyfive Mile Rapid (6), Cave Springs Rapid (5), Tiger Wash Rapid (5), and Twentynine Mile Rapid (2).

All the boats made it through the rapids without incident, until (I think) Tiger Wash. As we slipped over the tongue of the rapid, I thought I saw one of the boats go vertical, and someone tumbled out. I thought it was my nephew at first, but soon found that it was the boat with my brother and his wife. Somehow they had stayed in the boat, but unbeknownst to them, their oarsman was missing. They heard him say something along the lines of "your oarsman is NOT in the boat". They looked behind in surprise as he clawed his way back onto the raft just in time to get hung up on a boulder. Our raft was closest, so Pete rowed back into the eddy, and we started to climb up the rocks to see if we could assist, but they managed to back off the rock, and we were able to continue on.

Looking up the canyon, we could see that the monsoon storms were not finished. The towering cumulus clouds were wreaking havoc upstream, but the day remained sunny and clear for us. Tonight I would be sleeping under the stars.

We passed another stunning example of mass wasting just before hitting the Roaring Twenties. Boulder Narrows is a huge single chunk of Esplanade Sandstone that practically dams the river (below). According to the river guide, it is the single largest boulder to be found in the river through the Grand Canyon.

The canyon became deeper and more vertical.

At lunch, I was able to concentrate on smaller things, like the wonderfully colored and patterned river boulders.

The Supai Group is one of the thickest units in the Grand Canyon sequence at more than a thousand feet, so it was with us for quite a few miles. I had not been this close to the redbeds in a long time, and the ledges and cliffs made for a scenic stretch along the river. The combination of scenery, geology and rapids made for a memorable day.

There was an otherworldly appearance to the cliffs that rose above us, straight out of the river.

At mile 23, a new layer appeared, hard ledges of gray limestone. We had reached the Mississippian-aged Redwall Limestone. There wasn't a bit of red in it, at first, but that would change before long. I'll save the detailed description for the next post, because today's exposures were just a preliminary tease.

The Redwall Limestone is a true cliff-forming rock, and in places the rock hung over the river.

After the excitement of eleven major rapids and a near miss in the flip department, Pete was a bit tired. We were past the rapids of the Roaring Twenties, so I took to the oars for a couple of miles. I'm not saying I'm a natural oarsman, but the several miles I rowed probably amounted to about a half mile of actual river. I had a devil of a time sticking with the current and staying out of the eddies. Plus, you can see I didn't put on my gloves, so I also got a blister (whine, whine). It was fun!

In the next post: the incredible Redwall Limestone of Marble Canyon.