If These Cliffs Could Talk: Tis-sa-ack and Tu-tok-a-nu-la (A Geologic Love Story Redux)

I've been to Yosemite Valley twice in the last month, including a day when the Merced River was still at flood stage. I was reflecting on the many journeys I've made there with my students and with Mrs. Geotripper, and what a stunning place it truly is. I was thinking of a new angle to present some pictures of the latest trips, but then my good friend @phaneritic on Twitter asked a question about quotes concerning the valley that don't involve the writings of John Muir (as wonderful and poetic as his words were). I realized I had written about some of the legends of Yosemite a few years ago, and decided it was time to bring some of them back, in case they were missed before.

These stories also have relevance to the moment because of the decidedly stupid legal war over trademarks being waged between the National Park Service and the recently departed Delaware North concessionaire. One current sign of the ongoing legal battle is the new name for the Ahwahnee Hotel ("Majestic Yosemite") and Curry Village ("Half Dome Village"). Half Dome is a very plain name for such a stupendous rock, and I am thinking the park service missed an opportunity. Tis-sa-ack Village might have been a mouthful to pronounce, but it gives the rock a history and an air of mystery.

And so here it is, the story of Tis-sa-ack and Tu-tok-a-nu-la, a geologic love story, first published in November 14, 2014:

Tis-sa-ack (Half Dome) from near Yosemite Falls

A love story...

Unnumbered snows have come and gone since The Great Spirit led a band of his favorite children into the mountains, and bade them rest in this beautiful Valley of Ah-wah-nee. They were weary and footsore, and were glad to rest after their long journey. Here they found food in abundance. The streams held swarms of fish, meadows were knee-deep in sweet clover, great herds of deer roamed the forests in the Valley, and on the high mountains, oak trees were bending under the weight of their acorns, grass seeds and wild fruits and berries grew in bountiful profusion. Here they stayed and built their villages. They were happy, and multiplied, and prospered and became a great nation.

North Dome, Washington Column, and Half Dome in the clouds

How many stories begin in paradise?

I find the myths of different cultures to be fascinating. They provided their people with an explanation of the unexplainable, a comforting story that suggests there is order in the apparent chaos of the universe. In the perspective of geology, we can sometimes see the whispers of eyewitnesses to significant geologic events: the eruption of Mt. Mazama, for instance, which resulted in the formation of Crater Lake, is described in Native American oral histories. In this post we see one of the legends of Yosemite Valley, with all the embellishments and cultural biases of a 1922 narrative. Still, it's a good story

To their chief came a little son to gladden his heart. They wanted this son to become a great chief, capable of the leadership of a great people. He was made to sleep in the robes of the skins of the beaver and the coyote, that he might grow wise in building and keen of scent. As he grew older he was fed the meat of the fish, that he might become a strong swimmer, and the flesh of the deer, that he might be light and swift of foot. He was made to eat the eggs of the great crane, that he might be keen of sight. He was wrapped in the skin of the monarch of the forest, the grizzly bear, that he might grow up fearless and strong in combat. 

So many stories come with the hero, and the most interesting stories have heroes with flaws...they had everything. But then things happen. The world and the people who live in it are not perfect. And frankly, life would not be interesting.

And, when he grew to manhood, he was a great chief and beloved of all the people. His people prepared for him a lofty throne on the crown of the great rock which guards The Gateway of the Valley, and he was called Tu-tok-a-nu-la, after the great cranes that lived in the meadow near the top. The people of Ah-wah-nee were happy, for Tu-tok-a-nu-la was a wise and a good ruler. From his high rocky throne he kept watch over the Valley and the people whom he loved. He called on The Great Spirit who sent timely rains, so that the acorns grew in abundance, the hunters returned from the forests with game, and the fishermen from the streams with fish. There was peace and plenty throughout the Valley of Ah-wah-nee, and when Tu-tok-a-nu-la held speech with his people from his high throne his voice was deep and strong like the deep sound of the waterfall.

Tis-sa-ack from Sentinel Bridge

But paradise can't last forever. Trouble was coming, or more to the point, the trouble lay hidden in the heart of the hero, and it was about to be made manifest. There were no doubt all kinds of communications between the many Native American bands in California, and the trading of knowledge and technology. I'm sure this led to problems at times as well.

One day as Tu-tok-a-nu-la sat gazing into the glowing colors of the west, he saw approaching his valley a strange people, led by a maiden of wondrous loveliness. He called to them and the maiden answered him, saying, "It is I, Tis-sa-ack. We have come from the land of my people in the far south to visit with you. We have heard of the great and good chief, Tu-tok-a-nu-la, of his great people and his wonderful valley. We bring presents of baskets and beads and skins. After we have rested we will return to my people in the far south." Tu-tok-a-nu-la welcomed the fair visitor from the land to the
south and had prepared for her and her people a home on the summit of the great dome at the eastern end of the Valley. There she stayed and taught the women of Ah-wah-nee the arts of her people. Tu-tok-a-nu-la visited her often in her mountain home. He was charmed by her wonderful beauty and sweetness, and begged her to stay and become his wife, but she denied him, saying: "No, I must soon return with my people to their home in the far south." And, when Tu-tok-a-nu-la grew importunate in his wooing, she left her home in the night and was never seen again.
 

To-ko-ya (North Dome), Nangas (Washington Column) and Tis-sa-ack (Half Dome) from Glacier Point. The Ahwiyah Point rockfall scar is visible just right of center below Half Dome.

The perfect women, the Helen of Troy, the Eve. Of course, perfection is a tricky concept, subject to many biases and assumptions. It doesn't much take into account the actual relationship between those involved. As Mr. Spock mentioned in a famous episode of Star Trek: "After a time, you may find that having is not so pleasing a thing after all as wanting". Bad things are about to happen.

I admit, I've never heard the word importunate before. 

When the great chief knew that she was gone, a terrible loneliness and sorrow came to him, and he wandered away through the forests in search of her, forgetting his people in Ah-wah-nee. So strong was his love for her, and so deep his sorrow, that he forgot to call upon The Great Spirit to send the timely rains. So great was his neglect that the streams grew smaller and smaller and finally became dry. The crops failed. The hunters came back from the forests without meat, and the fishermen returned from the streams empty-handed. The leaves and the green acorns fell from the trees, and the bright flowers and green grasses became dry and brown.

From Washburn Point it is obvious that Half Dome isn't just a boring name, it is a mathematically wrong name. Three-Quarter Dome, maybe. I would just go with Tis-sa-ack

This is where the geologist in me starts paying attention. California has droughts, and there is evidence of mega-droughts that lasted more than a century. Check out this post for some of the striking evidence. These droughts both occurred within the last 2,000 years, recently enough to be remembered in the oral histories of a people.

And then things get interesting in a hurry...

The Great Spirit became very angry with Tu-tok-a-nu-la. The earth trembled with his wrath so that the rocks fell down into the Valley from the surrounding cliffs. The sky and the mountains belched forth smoke and flame. The great dome that had been the home of Tis-sa-ack, was rent asunder and half of it fell into the Valley. The melting snows from the high mountains came down into the Valley in a flood and drowned hundreds of the people. But the wrath of The Great Spirit was quickly spent, and the heavens again grew quiet. The floods receded, the sun shone, and once more peace and calm reigned over Ah-wah-nee. The life-giving moisture from the renewed streams crept into the parched soil. The oak trees put on new leaves and acorns. The grasses again became fresh and green, the flowers lifted their drooping heads and took on their old gay colors. The fish came back to the streams, and the game to the forests.

Wow.

"The earth trembled...so that the rocks fell down into the Valley from the surrounding cliffs". Earthquakes have rocked California for a lot longer than humans have been around, and no doubt played an important part in causing mass wasting within the valley. John Muir experienced the 1872 Lone Pine earthquake while in Yosemite Valley (magnitude 7.8 or higher) and witnessed the collapse of a cliff. I've witnessed a few small rockfalls that I will never forget. Imagine the impact of a really large quake and the accompanying rock falls on the collective memory of a people.

"The sky and mountains belched forth smoke and flame". Yosemite lies just west of the Long Valley Caldera and the Mono Craters, and eruptions have occurred there as recently as a few hundred years ago. Imagine the impact of a fair-sized eruption over the mountains on a people who maybe had never witnessed such a thing, or only heard about it in legends.

"The melting snows from the high mountains came down into the Valley in a flood and drowned hundreds of the people." It's not hard to imagine the impact of a Pineapple Express (an atmospheric river storm) falling onto a thick snowpack in the mountains above Yosemite Valley. Such an event took place in 1997 (be sure to check out the video). Much of the valley floor was covered by as much as 6-8 feet of water, and the event was devastating to the human developments in Yosemite Valley.


Ironically, the natural environment was far less devastated. The ecosystem of Yosemite evolved in an environment of occasional huge floods, and life sprang back quickly.

And, when the Valley was once again clothed in beauty and plenty, there appeared on the rent face of the dome which had been her home, the beautiful face of Tis-sa-ack, where it can still be seen to this day. And the dome was named Tis-sa-ack, in memory of the fair visitor who had been loved by all the people of Ah-wah-nee. At the same time, that all might hold his memory in their hearts, there appeared on the face of the great rock supporting his throne, the majestic figure of the great chief, dressed in a flowing robe and pointing a finger to where he had gone, to El-o-win, the happy land beyond the setting sun.

And thus we have the story of how Half Dome, Washington Column, and North Dome came to be. I am struck by how lifeless these names actually are, and I wish we could see their names changed to reflect the very interesting stories of their origins.

We have stories too of the formation of how these rocks came to be. They involve the formation of granitic magma deep in the hellish regions of the Earth's crust, the intrusion and cooling of the granite, the uplift and erosion of the rocks by rivers and glaciers, and the shaping of the rocks by the working of jointing, exfoliation, ice, and mass wasting. It's a good story, based on careful observations, but the ancient legends? They were based on careful observations as well. The Native Americans maybe didn't have the technology we have today, but they did a pretty good job of describing the phenomena, and designing models to explain their observations. 
 
This version of the Half Dome story is from The Lore and the Lure of The Yosemite by Herbert Earl Wilson, published in 1922. Another legend of Half Dome involves an argument between a husband and wife, with thrown baskets and other unpleasantness. I like the story above better!

Perhaps a Last Look at Some Yosemite High Country (for the Winter, Anyway)

"Half" Dome from Washburn Point

I made the trek up the hill to see Yosemite last weekend, with a field trip on the valley floor on Saturday with my students, and a quieter tour in the high country with Mrs. Geotripper on Sunday. We headed up Glacier Point Road to gain a unique perspective on Yosemite Valley and the higher country above. With a fairly powerful storm arriving tonight, it is at least conceivable that the road could close for the winter due to snow. There was certainly a mood of closing down. The road was uncrowded, and so were the parking lots. The curio shop at Glacier Point was closed for the season.

Yosemite high country, with Mt. Broderick, Liberty Cap, and Nevada Fall in the foreground.

Many people who travel to Glacier Point tend to be single-minded in their quest, and often miss one of the truly spectacular viewpoints the road has to offer: Washburn Point. It is perched at the 7,400 foot level above the Merced River directly across from "Half" Dome. It is from this point that the misnomer is most obvious. If anything, Half Dome should have been named "Four-fifths Dome".

Nevada Fall on the upper Merced River

There is a stupendous view towards the high country of Little Yosemite Valley and the headwaters of the Merced River. The effect of glaciation is apparent everywhere. Glacial stairsteps, caused by pervasive vertical fractures in the granite ("joints"), were the origin of the two major waterfalls on the Merced River, Nevada Fall (594 feet, above), and Vernal Fall (317 feet, below). Along the skyline above, the glacially-carved horns, aretes, and cirques can be seen. It's wild and beautiful country.

Vernal Fall from Washburn Point

I imagine Washburn Point gets less traffic than Glacier Point because it doesn't look down on the main part of Yosemite Valley. That's okay with me. It's notable that not a single road is visible from Washburn. One is looking at wilderness, something that is sorely lacking in the more populated parts of Yosemite National Park.

North Dome and Basket Dome on the north side of Yosemite Valley. Mt. Hoffman rises in the distance.

A Series of Fortunate Events: Glacier Point, Living Up to the Hype

Glacier Point on the rim of Yosemite Valley is hands-down one of the most spectacular places one can stand in the world. There's just no place like it. And it's noisy. It's crowded. There is a busy and often full parking lot. And despite that, it is worth putting up with, because there just aren't that many places where you can look straight down for 3,000 feet, and at the same time see the iconic rocks of the upper valley from a unique angle.

It takes a little effort to get there. One has to drive about 25 miles from the floor of Yosemite Valley up a narrow winding road. One has to wade through the crowds to get the edge of the precipice. But no matter how many times I've stood there, I can never fail to be in awe that such places exist. In one sweeping view one can see the north valley wall from the vicinity of the Three Brothers and Yosemite Falls, past Yosemite Point, on to North Dome and Basket Dome, across the deep trough of Tenaya Canyon to Half Dome. And below your feet there is the floor of Yosemite Valley, the meadows, the forests, the parking areas, the resorts, all from a nearly vertical perch at 3,200 feet (980 m).

It's from a high point like this one that I can best appreciate the work of the glaciers that altered a narrow river-carved canyon into the wide, flat floor we see today. The earliest glaciers filled the valley to the rim (the Pre-Tahoe stage around 800,000 years ago), while the later advances only filled the valley to one-third or so of the total depth (the Tahoe stage at 130,000-65,000 years, and the Tioga stage from 20,000 to 13,000 years ago). The domes, like North Dome, Basket Dome and Half Dome, rose above the ice at all times. Their rounded shapes are the result of exfoliation, the tendency of slabs to break off the edges and corners of solid monoliths of granitic rock as erosion took weight off the surface of the rock. Glaciers helped excavate the rock from the jointed face of Half Dome, but never overtopped the gigantic rock.

One might think that a view like this is unchanging on a human time scale, but that's not exactly true. It's a little tricky to see it in the shadows, but look at the whitish exposure of granite to the left of Half Dome in the picture above. That scar didn't exist prior to 2009. Every visitor prior to March of that year saw something different. The Ahwiyah slide involved thousands of tons of rock that fell 1,800 feet to the floor of Tenaya Canyon. The resulting explosion of rock destroyed hundreds of trees on the valley floor. To see some before and after pictures, click here for a look.

Our class finished at Glacier Point and headed back the vehicles, but we weren't done with standing in dramatic places. That will be in the next post!

If These Cliffs Could Talk: Tis-sa-ack and Tu-tok-a-nu-la (A Geologic Love Story)

Tis-sa-ack (Half Dome) from near Yosemite Falls

A love story...

Unnumbered snows have come and gone since The Great Spirit led a band of his favorite children into the mountains, and bade them rest in this beautiful Valley of Ah-wah-nee. They were weary and footsore, and were glad to rest after their long journey. Here they found food in abundance. The streams held swarms of fish, meadows were knee-deep in sweet clover, great herds of deer roamed the forests in the Valley, and on the high mountains, oak trees were bending under the weight of their acorns, grass seeds and wild fruits and berries grew in bountiful profusion. Here they stayed and built their villages. They were happy, and multiplied, and prospered and became a great nation.

North Dome, Washington Column, and Half Dome in the clouds

How many stories begin in paradise?

I find the myths of different cultures to be fascinating. They provided their people with an explanation of the unexplainable, a comforting story that suggests there is order in the apparent chaos of the universe. In the perspective of geology, we can sometimes see the whispers of eyewitnesses to significant geologic events: the eruption of Mt. Mazama, for instance, which resulted in the formation of Crater Lake, is described in Native American oral histories. In this post we see one of the legends of Yosemite Valley, with all the embellishments and cultural biases of a 1922 narrative. Still, it's a good story

To their chief came a little son to gladden his heart. They wanted this son to become a great chief, capable of the leadership of a great people. He was made to sleep in the robes of the skins of the beaver and the coyote, that he might grow wise in building and keen of scent. As he grew older he was fed the meat of the fish, that he might become a strong swimmer, and the flesh of the deer, that he might be light and swift of foot. He was made to eat the eggs of the great crane, that he might be keen of sight. He was wrapped in the skin of the monarch of the forest, the grizzly bear, that he might grow up fearless and strong in combat. 

So many stories come with the hero, and the most interesting stories have heroes with flaws...they had everything. But then things happen. The world and the people who live in it are not perfect. And frankly, life would not be interesting.

And, when he grew to manhood, he was a great chief and beloved of all the people. His people prepared for him a lofty throne on the crown of the great rock which guards The Gateway of the Valley, and he was called Tu-tok-a-nu-la, after the great cranes that lived in the meadow near the top. The people of Ah-wah-nee were happy, for Tu-tok-a-nu-la was a wise and a good ruler. From his high rocky throne he kept watch over the Valley and the people whom he loved. He called on The Great Spirit who sent timely rains, so that the acorns grew in abundance, the hunters returned from the forests with game, and the fishermen from the streams with fish. There was peace and plenty throughout the Valley of Ah-wah-nee, and when Tu-tok-a-nu-la held speech with his people from his high throne his voice was deep and strong like the deep sound of the waterfall.

Tis-sa-ack from Sentinel Bridge

But paradise can't last forever. Trouble was coming, or more to the point, the trouble lay hidden in the heart of the hero, and it was about to be made manifest. There were no doubt all kinds of communications between the many Native American bands in California, and the trading of knowledge and technology. I'm sure this led to problems at times as well.

One day as Tu-tok-a-nu-la sat gazing into the glowing colors of the west, he saw approaching his valley a strange people, led by a maiden of wondrous loveliness. He called to them and the maiden answered him, saying, "It is I, Tis-sa-ack. We have come from the land of my people in the far south to visit with you. We have heard of the great and good chief, Tu-tok-a-nu-la, of his great people and his wonderful valley. We bring presents of baskets and beads and skins. After we have rested we will return to my people in the far south." Tu-tok-a-nu-la welcomed the fair visitor from the land to the
south and had prepared for her and her people a home on the summit of the great dome at the eastern end of the Valley. There she stayed and taught the women of Ah-wah-nee the arts of her people. Tu-tok-a-nu-la visited her often in her mountain home. He was charmed by her wonderful beauty and sweetness, and begged her to stay and become his wife, but she denied him, saying: "No, I must soon return with my people to their home in the far south." And, when Tu-tok-a-nu-la grew importunate in his wooing, she left her home in the night and was never seen again.
 

To-ko-ya (North Dome), Nangas (Washington Column) and Tis-sa-ack (Half Dome) from Glacier Point. The Ahwiyah Point rockfall scar is visible just right of center below Half Dome.

The perfect women, the Helen of Troy, the Eve. Of course, perfection is a tricky concept, subject to many biases and assumptions. It doesn't much take into account the actual relationship between those involved. As Mr. Spock mentioned in a famous episode of Star Trek: "After a time, you may find that having is not so pleasing a thing after all as wanting". Bad things are about to happen.

I admit, I've never heard the word importunate before. 

When the great chief knew that she was gone, a terrible loneliness and sorrow came to him, and he wandered away through the forests in search of her, forgetting his people in Ah-wah-nee. So strong was his love for her, and so deep his sorrow, that he forgot to call upon The Great Spirit to send the timely rains. So great was his neglect that the streams grew smaller and smaller and finally became dry. The crops failed. The hunters came back from the forests without meat, and the fishermen returned from the streams empty-handed. The leaves and the green acorns fell from the trees, and the bright flowers and green grasses became dry and brown.

From Washburn Point it is obvious that Half Dome isn't just a boring name, it is a mathematically wrong name. Three-Quarter Dome, maybe. I would just go with Tis-sa-ack

This is where the geologist in me starts paying attention. California has droughts, and there is evidence of mega-droughts that lasted more than a century. Check out this post for some of the striking evidence. These droughts both occurred within the last 2,000 years, recently enough to be remembered in the oral histories of a people.

And then things get interesting in a hurry...

The Great Spirit became very angry with Tu-tok-a-nu-la. The earth trembled with his wrath so that the rocks fell down into the Valley from the surrounding cliffs. The sky and the mountains belched forth smoke and flame. The great dome that had been the home of Tis-sa-ack, was rent asunder and half of it fell into the Valley. The melting snows from the high mountains came down into the Valley in a flood and drowned hundreds of the people. But the wrath of The Great Spirit was quickly spent, and the heavens again grew quiet. The floods receded, the sun shone, and once more peace and calm reigned over Ah-wah-nee. The life-giving moisture from the renewed streams crept into the parched soil. The oak trees put on new leaves and acorns. The grasses again became fresh and green, the flowers lifted their drooping heads and took on their old gay colors. The fish came back to the streams, and the game to the forests.

Wow.

"The earth trembled...so that the rocks fell down into the Valley from the surrounding cliffs". Earthquakes have rocked California for a lot longer than humans have been around, and no doubt played an important part in causing mass wasting within the valley. John Muir experienced the 1872 Lone Pine earthquake while in Yosemite Valley (magnitude 7.8 or higher) and witnessed the collapse of a cliff. I've witnessed a few small rockfalls that I will never forget. Imagine the impact of a really large quake and the accompanying rock falls on the collective memory of a people.

"The sky and mountains belched forth smoke and flame". Yosemite lies just west of the Long Valley Caldera and the Mono Craters, and eruptions have occurred there as recently as a few hundred years ago. Imagine the impact of a fair-sized eruption over the mountains on a people who maybe had never witnessed such a thing, or only heard about it in legends.

"The melting snows from the high mountains came down into the Valley in a flood and drowned hundreds of the people." It's not hard to imagine the impact of a Pineapple Express (an atmospheric river storm) falling onto a thick snowpack in the mountains above Yosemite Valley. Such an event took place in 1997 (be sure to check out the video). Much of the valley floor was covered by as much as 6-8 feet of water, and the event was devastating to the human developments in Yosemite Valley.


Ironically, the natural environment was far less devastated. The ecosystem of Yosemite evolved in an environment of occasional huge floods, and life sprang back quickly.

And, when the Valley was once again clothed in beauty and plenty, there appeared on the rent face of the dome which had been her home, the beautiful face of Tis-sa-ack, where it can still be seen to this day. And the dome was named Tis-sa-ack, in memory of the fair visitor who had been loved by all the people of Ah-wah-nee. At the same time, that all might hold his memory in their hearts, there appeared on the face of the great rock supporting his throne, the majestic figure of the great chief, dressed in a flowing robe and pointing a finger to where he had gone, to El-o-win, the happy land beyond the setting sun.

And thus we have the story of how Half Dome, Washington Column, and North Dome came to be. I am struck by how lifeless these names actually are, and I wish we could see their names changed to reflect the very interesting stories of their origins.

We have stories too of the formation of how these rocks came to be. They involve the formation of granitic magma deep in the hellish regions of the Earth's crust, the intrusion and cooling of the granite, the uplift and erosion of the rocks by rivers and glaciers, and the shaping of the rocks by the working of jointing, exfoliation, ice, and mass wasting. It's a good story, based on careful observations, but the ancient legends? They were based on careful observations as well. The Native Americans maybe didn't have the technology we have today, but they did a pretty good job of describing the phenomena, and designing models to explain their observations. 
 
This version of the Half Dome story is from The Lore and the Lure of The Yosemite by Herbert Earl Wilson, published in 1922. Another legend of Half Dome involves an argument between a husband and wife, with thrown baskets and other unpleasantness. I like the story above better!

Half Dome is down to a Quarter! Will Anyone Want to Visit Yosemite?

OK, not really, I'm just continuing a brief series on Yosemite Valley encouraging folks to look behind and to the side of the iconic features like Half Dome, El Capitan, Yosemite Falls and Bridalveil Fall. Our "high-water journey" to Yosemite Valley last week included an excursion to Glacier Point, which had opened to visitors only a few days prior.

The views from Glacier Point, and the usually quieter Washburn Point, were spectacular, as they almost always are. Half Dome dominates the views, so I was trying to take a few shots that didn't have the granite monolith in the center. They appear below.

I am always struck by the grandeur of Tenaya Canyon, the main tributary valley to the Merced River that meets the Merced at the head of Yosemite Valley. I call it a tributary "valley" because Tenaya Creek is a relatively underfit stream, quite incapable of carving such a deep valley, one that rivals the Grand Canyon in depth.

Even the glaciers shouldn't have been big enough to carve such an impressive gorge, and they wouldn't have except that the vast ice sheet that covered the Tuolumne Meadows area to the north spilled over and contributed a vast amount of ice to the otherwise small Tenaya glacier system.
It was a week of the highest snow runoff, with the Merced River running at 7,000 cubic feet per second, about three times normal. So with a zoom shot, I was able to spy the rarely viewed Pywiack Cascades, in a trailless and inaccessible part of Tenaya Creek Canyon (an interesting description of the high adventure journey through this gorge can be found here). I would love to make that journey, but I'm getting just a bit old for such ventures!

If Half Dome didn't exist, North Dome and Basket Dome would certainly command more attention. Unlike Half Dome, these lower domes were probably covered by ice during the most intense glaciations, but in the last 800,000 years most of the shaping has been accomplished by exfoliation. Exfoliation is a form of unloading, in which the granite expands as it is exposed by erosion, cracking into slabs running parallel to the surface of the rock. The slabbing tends to break off corners and edges, leading to the characteristic dome shape.

The view from Glacier Point changed forever in March of 2009 when a huge rockfall, the biggest in two decades, thundered off of Ahwiyah Point below the cliffs of Half Dome. The light colored strip running across the photo above shows the path of the slab, and the pile of talus in the shadow shows the impact point. Hundreds of trees were blown down, and a popular hiking trail was covered, but luckily no one was hurt.

I know it is hard to see the view from Glacier and Washburn without actually noticing Half Dome, and so I did take quite a few pictures of it. One of them is below, if you are feeling only half-satisfied by the rest of the post!

Staring into the Abyss #4 - Yosemite as you (maybe) have never seen it (and my 100th Post!)

Today is the four-month anniversary and the 100th post on Geotripper! I wasn't really sure what it was going to be like, and whether I would be able to keep the site active with all of the other stuff going on in my life as a college teacher, but I have made it work by allowing myself a blog entry as a reward for finishing a pile of grading. And there are always piles of grading! But I have enjoyed sharing my photographs and opinions, and I have especially appreciated the positive feedback that I have received from the geoblogosphere. I enjoy being a part this interesting group of earth scientists, and I hope to see more of the students and teachers out there getting involved! It was far easier to start a blog than I thought it would be and it has been rewarding. Now I will have to see if I can make it all the way through a year!

Today's view of the abyss comes from a familiar tourist stop: Glacier Point. It is accessible by paved road and trail, and is visited by hundreds of thousands of people every year. It is easily one of the greatest scenic vistas on the planet. The view is dominated by Half Dome and the Tenaya Canyon, as well as the cliffs around Yosemite Falls. Between the two is an interesting view of a pair of exfoliation domes called North Dome (left) and Basket Dome (right). From the valley floor they are barely visible above Royal Arches and Washington Column.

Exfoliation takes place when the weight is removed from homogeneous rock like granite, and the rock expands. It fractures parallel to the surface and this leads to a tendency to remove corners and edges of otherwise rectangular rocks. A great many domes grace the Sierra Nevada, and a vast number of them have never been touched by glaciers.

The mountain on the skyline is Mt. Hoffman, which is a high peak close to the geographic center of Yosemite National Park. N. King Huber used the view from the summit as the springboard to a discussion of the geology of the park in his excellent Geologic Story of Yosemite National Park. It is a great hike, and is likely to be the subject of future posts.