Archive for the ‘plate tectonics’ Tag

The Tragedy in Nepal   19 comments

Soulful bells echo through the mountains at dawn, calling the monks to prayer at Tangboche Monastery.

I want so much to be able to return to the mountain kingdom of Nepal and help them in their hour of need.  To see all those wonderful people again would be so great.  That may seem a strange thing to say.  But I know for a fact that even in the midst of tragedy they remain an optimistic and warm people.  Right now I’m missing them and praying for their safety.  I wanted to post some pictures of Nepal that I’ve never shared, and also go into some background on how and why this happened.

THE GEOLOGIC STORY

You may have heard that Mt. Everest is getting taller, and we just saw dramatic and horrific evidence of that fact.  India collided with south Asia some 55 million years ago, and the mighty Himalayas began then.  But that slow motion and awesome event continues today, as huge slabs of the earth’s crust continue to be shoved beneath the Tibetan Plateau.  The zone where they come together, along the 2400 km. (1500 mile) long Himalayan mountain front is complex.  But north-directed subduction, or underthrusting, is the dominant process.

Mount Everest

Mount Everest

Ama Dablam in black and white.

Ama Dablam in black and white.

The earth’s most recent and currently most dramatic tectonic collision has resulted in shortening of northern India and southern Nepal, bringing Delhi and Lhasa closer together.  This in turn causes the crust to greatly thicken (mostly in the downward direction).  In other words, most of the long mountain range lies beneath sea level.  Like a giant iceberg, active mountain ranges have roots that are hundreds of times more voluminous than their visible parts.  The north-south shortening doesn’t just create crustal thickening; it also causes the region to widen in an east-west direction via a series of large strike-slip faults (like the San Andreas).

Namche Bazaar, Nepal

Namche Bazaar, Nepal

Having climbed Everest 8 times in his career, this Sherpa I met taking a walk above his home village had a great way about him.

Having climbed Everest 8 times in his career, this Sherpa I met taking a walk above his home village had a great way about him.

Deep beneath the Himalaya, collision takes the form of a slow, hot, plastic deformation.  There are no sudden jerking motions.  But in shallower regions, where the rocks are cooler and brittle, this is impossible.  Instead, the stress builds up until it’s finally released with a sudden rapid slide along a plane of weakness (or fault).

It is at those times that we on the surface of this planet are reminded that ours is a dynamic planet.  These events, which can vary from a gentle rocking that lasts only seconds and which you only notice if you are in a quiet place to violent minutes-long shaking that can bring down buildings and even whole mountainsides, are called earthquakes.

A woman in the Himalaya of Nepal is proud of her vegetable garden, and her grandson.

A woman in the Himalaya of Nepal is proud of her vegetable garden, and her grandson.

3 man at airport

Waiting for weather to clear at Lukla, this gentleman’s beard was too cool I had to talk to him.

 

The earthquake of April 25th was centered about 80 km. (50 miles) NW of Kathmandu,  It was magnitude 7.8 on the Richter scale.  It was located about 15 km. (9+ miles) deep.  That is fairly shallow for a quake of this size.  Combined with the dense population and low quality of construction in most of the region, this made for a major disaster.  Considering what is going on here, the coming together of two of Earth’s greatest tectonic plates, historic earthquakes are relatively few.  The last one to affect the same area was in 1988 and killed 1500.  The 1934 Bihar earthquake killed some 10,600 and severely damaged Kathmandu.

Two young Sherpa friends haul equipment on the trail to Namche Bazaar in Nepal.

Two young Sherpa friends haul equipment on the trail to Namche Bazaar in Nepal.

I don't like thinking about the orphans.

I don’t like thinking about the orphans.  Just too sad!

 

Most of the people here, with the resources to live from day to day and not much more, have been deeply affected by this disaster.  The current count is over 4000 and still rising.  Many people live far from roads, so the final tally could take weeks or even months.  Undoubtedly many of the deaths will turn out to be caused by major landslides.  In any mountainous region, a big quake leads to landslides of epic size.  Snow avalanches also occurred in the alpine regions, including one caught on video that roared down the south side of Everest and hit base camp.

The spectacular Khumbu Himal.

The spectacular Khumbu Himal.

They are sacred but with the wonder they inspire comes a dangerous dynamism.

They are sacred but with the wonder they inspire comes a dangerous dynamism.

So much misery can be brought by earthquakes.  They strike without warning of course, and this makes them truly terrifying.  I have been in a few small ones, and get a visceral thrill out of it.  I get the same feeling witnessing a volcanic eruption.  That’s partly because I’m a geologist and know about the connection between a living breathing planet and life.  But I’m sure my reaction would be one of pure terror if and when I’m caught in a truly big event.  Once, in 1999, I flew out of Istanbul less than 24 hours before a major quake hit that city, killing 17,000.

Getting to spend time in a Sherpa kitchen, drinking tea, is a special thing.

Getting to spend time in a Sherpa kitchen, drinking tea, is a special thing.

A friend who suffered a broken leg in the quake but otherwise is okay.

I played around with this little Sherpa girl as her mother sewed in a small sun-warmed courtyard.  She is a teenager now.

I played around with this little Sherpa girl as her mother sewed in a small sun-warmed courtyard. She is a teenager now.

A Gurkha I met whitewater rafting, he emigrated to Hong Kong, and hosted me there.  Nepalis are so nice!

A Gurkha I met whitewater rafting, he emigrated to Hong Kong, and hosted me there. Nepalis are so nice!

Please give if you can to the legitimate aid organizations helping in Nepal.  And in any case, please keep those beautiful souls in your thoughts and prayers.  I’ve never seen a harder working people.  I’m sure they will recover, but big aftershocks continue as I’m writing this.

Friends of mine are camped outside in pouring rain, afraid to return to their homes.  So right now I’m hoping and praying the aftershocks are many and small, not fewer and large.  Namaste to all Nepalis and all those who have connections to the country.

I'm holding up the rafting party, but I wanted these kids to say Namaste without laughing, haha!

I’m holding up the rafting party, but I wanted these kids to say Namaste without laughing, haha!

Stupa at Boudhanath

Alpenglow over the Khumbu

 

 

 

The Cascades I: Volcanoes Give and Take Away   16 comments

Sunrise on the north side of Mt Hood from the pastoral Hood River Valley, Oregon.

Sunrise on the north side of Mt Hood from the pastoral Hood River Valley, Oregon.

This is the mountain range I’m most familiar with, my home range.  I’ve climbed all of the high Oregon Cascades and many of the bigger Washington ones as well.  So I have personal experience and knowledge of these peaks.  Named for the many waterfalls that tumble over their volcanic cliffs, the Cascades are essentially a northern analogue of the Andes in South America.

The waterfalls for which the Cascades are named occur all through the range, including here at Toketee Falls.

The waterfalls for which the Cascades are named  include Toketee Falls.

GEOGRAPHY

The Cascades are volcanoes that still erupt from time to time, but with the exception of a single mountain are not the most active volcanic chain in the world by any means.  More on the exception below.  The Cascade Range, which stretches for 700 miles (1100 km.) in a north-south direction from Mount Garibaldi in Canada to Mount Lassen in California, is part of the Pacific Ring of Fire (see below).  This whole region of the western Pacific Northwest is often called Cascadia.

The Cascades are dotted with beautiful mountain lakes.

The Cascades are dotted with beautiful mountain lakes.

The dramatic and beautiful mountains that make up the Cascades in most cases exceed 10,000 feet (3000 meters).  The high peaks are generally well-spaced, with many miles of forested lower mountains and hills between each snow-capped peak.  Oregon’s Three Sisters area (which actually includes 5 big volcanoes) is an exception to this wide spacing.  The bunched-up and much more rugged North Cascades in Washington are a whole different range geologically, one that happens to coincide in space (but not time) with the volcanoes of the Cascades.

A wet meadow in Crater Lake National Park blooms with pink monkeyflower, among other flowers.

A wet meadow in Crater Lake National Park blooms with pink monkeyflower, among other flowers.

GEOLOGY

The highest peaks in the Cascades are quite young, most less than 100,000 years old – a moment in the earth’s 4.5 billion-year history.  They are built upon a much older eroded volcanic range, arranged along an axis situated slightly to the west of the present locus of volcanic activity.  These older volcanoes began erupting some 37 million years ago.  It’s lucky for life (including us) that these older, heavily eroded volcanoes are around.  It’s the reason we have those lush forests, those cold streams that nourish the region’s great fish runs, and the habitat for the region’s other wildlife.  And let’s not forget the many waterfalls!

From high on Cooper Spur at Mount Hood, Oregon, the view north includes Mount Adams in Washington.

From high on Cooper Spur at Mount Hood, Oregon, the view north includes Mount Adams in Washington.

The older ancestral Cascades are also responsible for the region’s enormous timber resources plus the very rich soils that drew settlers west along the Oregon Trail.  Volcanoes combine with ample rainfall to make rich soil for farming.  By the way, many often wonder why so many people, worldwide, live near dangerous volcanoes.  It’s simple:  the rich soils around volcanoes, the productive farmland.  There is really not much choice.  We must eat, and so we must live near volcanoes.

While the Western Cascades are responsible for many of the Northwest’s assets, let’s not totally dismiss the younger High Cascades.  Their snowpack, lasting well into summer, gives farmers and ranchers (especially those to the east) water for their crops through typically dry summers.

The older western Cascades are very different in character than the high Cascades.

The older western Cascades are very different in character than the high Cascades.

The Cascades are stratovolcanoes (aka composite cones).  These are the steep-sided, conical volcanoes you drew as a kid in school.  They are made of alternating layers of lava-rock and pyroclastic (ash) deposits.  The volcanic rock is characteristically lighter colored than the basalt which covers the region to the east of the Cascades.  A typical volcanic rock for the Cascades is andesite (named for the Andes), which flows over the ground in a somewhat stickier manner than more fluid basalt (Hawaiian volcanoes erupt basalt).  The Cascades do have their share of basalt too, along with dacite and a few other types of volcanic rock.

An uncommon volcanic rock of the Cascades is obsidian.  It is very rich in silica (SiO2), which is also what quartz is made of.  In liquid lava, dissolved silica acts to make it stickier, more viscous.  Water does the opposite, makes lava less viscous – more fluid.  Obsidian is so rich in silica and erupts so dry that it literally squeezes out of the ground like thick toothpaste, heaping up into mounds and ridges.  Once cooled, obsidian is a beautiful natural glass, normally black, that can be sharp enough to serve as surgical instruments.  Obsidian arrowheads left along old American Indian trails and hunting grounds can still be found throughout the Northwest.

Admiring the view while on a climb in the Cascades.  That is Mount Adams in Washington.

Admiring the view while on a climb in the Cascades. That is Mount Adams in Washington.

THE RING OF FIRE AND PLATE TECTONICS

The Pacific Ring of Fire is that huge circle of volcanoes and earthquake activity that circles the Pacific ocean basin.  Some of the world’s most spectacular eruptions and devastating earthquakes happen along the Ring of Fire.  Truly an enormous geologic feature, it exists because the earth’s tectonic plates rub against and collide with each other (see addendum below if you don’t know about plate tectonics already).  Although they act slowly, the forces are gargantuan.  And something has to occasionally give.

The big snow-capped peaks of the Cascades are classic strato-volcanoes.

The big snow-capped peaks of the Cascades are classic strato-volcanoes.

One example of the power and beauty of the Ring of Fire lies in the remote Aleutian Islands and Russia’s Kamchatka Peninsula.  Here the huge Pacific Plate dives under the North American continental plate (plus a smaller one called the Okhotsk Plate) along a so-called subduction zone.  The plate partially melts as it descends, because of the heat of course – but also because of it is loaded with water (which acts as a flux).  Plumes of magma rising from the descending and melting plate eventually erupt into some of the world’s most active (and thankfully remote) volcanoes.  In the Southern Hemisphere on the opposite side of the Ring of Fire, the oceanic Nazca Plate subducts under the South American plate to form the longest volcanic range in the world, the Andes.

Crater Lake in Oregon fills the collapsed caldera of Mount Mazama, which blew its top about 7000 years ago.

Crater Lake in Oregon fills the collapsed caldera of Mount Mazama, which blew its top about 7000 years ago.

All throughout the Ring of Fire there are earthquakes.  Some of the largest happen as a result of subduction and are called megathrust quakes (how’s that for a name!).  The earthquake that caused the destructive Japanese tsunami of 2011 was of the  megathrust variety.  This enormous earthquake happened where the Pacific Plate subducts beneath Japan’s Honshu Island.  The Pacific Plate moved as much as 20 meters (66 feet) west during the minutes-long quake.  Honshu drew closer to America by about 2.5 meters (8 feet).  The equally destructive Indian Ocean tsunami of 2004 was also generated by a megathrust quake along a subduction zone.

Other earthquakes happen when two tectonic plates slide past each other.  The San Andreas in California is the most famous example of this so-called transform boundary.  Because these earthquakes happen on land and have fairly shallow epicenters, they can be very destructive.  This is despite the quakes being generally smaller than subduction-zone, megathrust earthquakes.

Climbing in the Cascades.  Mount Adams (right) and Rainier are visible.

Climbing in the Cascades. Mount Adams (right) and Rainier are visible.

ADDENDUM: PLATE TECTONICS

The crust of the earth (plus some extra beneath it) is broken into enormous semi-rigid plates.  Over time, the plates move across the planet’s surface, on average about as fast as your fingernails grow.  That’s an average; during big quakes they can move up to a hundred feet!  But overall it’s a very slow process.  It can take over a million years for a plate to move 50 miles.  They ride atop enormous convection currents in the semi-molten part of the upper mantle.  The mantle is that layer that lies directly beneath the earth’s crust.  The weight of tectonic plates as they descend into the mantle along subduction zones (like the one that lies just off the Pacific Northwest coast) helps to pull the oceanic plates along.

Why do we have tectonics while the other planets don’t seem to?  For one thing the energy that drives the convection currents comes from heat given off by the still cooling interior of the earth.   Mars is too small to have much heat left.  For Earth, much of the core is still molten, and our fast spin sets up complex circulation patterns (which cause our magnetic field).  Combined with heat from the decay of radioactive elements, this gives rise to huge, slowly rising zones of heat.  When they hit the colder, more rigid upper parts of the earth, the crust, the currents spread outward horizontally.

Silver Star Mountain in Washington, after a heavy snowfall.

Silver Star Mountain in Washington, after a heavy snowfall.

But there’s another reason for plate tectonics.  It is because we are a water planet that all this partly molten rock is around.  Venus is much too dry for plate tectonics to get going.  Without water the pressures deep below would not allow enough melting.  Water essentially lubricates the earth’s tectonic system.  And without plate tectonics complex life would most likely not be possible, yet another way water is crucial to a living earth.

This series will continue.  If you are interested in any of the images, just click on them.  They are copyrighted and not available for download without my permission.  Please contact me if you have any questions.  Thanks for reading!

Sunset over the Western Cascades, as viewed from Mount Hood in Oregon.

Sunset over the Western Cascades, as viewed from Mount Hood in Oregon.

Death Valley V: Geologic History   Leave a comment

The morning sun hits the Panamint Range, as viewed from Death Valley.

The morning sun hits the Panamint Range, as viewed from Death Valley.

This is the second of three posts on the natural history background for a visit to Death Valley National Park in California.  I hope it sparks some interest in these subjects, because if you visit this desert park, you will be hard-pressed to ignore its stunning geology and arid ecology.

GEOLOGIC HISTORY

The rocks exposed in Death Valley go back nearly two billion years.  As you walk through canyons like Titus or Marble, you will see layer upon layer of a dark gray sedimentary rock (often weathering red to orange).  A great thing to do on a hot day in a canyon is to go into the shade of these walls and lean your whole body against the cool gray rock.  This is limestone, and it tells of a time when this area was covered in a warm subtropical sea.

The famous Artist's Palette in Death Valley as viewed from atop the ridge that is most often photographed.

The famous Artist’s Palette in Death Valley as viewed from atop the ridge that is most often photographed.

Back in Paleozoic time (250-600 million years ago), there was a quiet coastline not far east of here one very similar to the modern Atlantic coast of North America.  Marine algae and other small creatures pulled CO2 and calcium out of the seawater to form their shells. These lime muds accumulated layer upon layer, eventually to become limestone.  Sand, silt and mud covered the shallow marine shelf at times, leading to sandstone, siltstone and shale.

Later, during the time of dinosaurs (the Mesozoic), the whole region was the focus of mountain building, thus emerging from the sea.  And mountain building means plate tectonics.  At that time, the ancestral Pacific Plate (called the Farallon Plate by geologists) pushed underneath the western edge of North America – a subduction zone.

Recently formed salt crystals decorate the floor of Death Valley in California.

Recently formed salt crystals decorate the floor of Death Valley in California.

The incredible pressures generated along this subduction zone made the limestone and other rocks pay dearly for being in the wrong place at the wrong time.  These sedimentary rocks were originally deposited in horizontal layers, and as you can easily see in the naked mountains of Death Valley, they have been folded, faulted, and otherwise tortured.  Masses of granitic magma, melted crustal rocks from below, pushed up into the sedimentary rocks.  This granite is best exposed to the south, in Joshua Tree and other parts of southern California.

A view of Death Valley from above Artist's Palette shows the playa with its salt pan.  A large alluvial fan is at upper left with dark inselbergs emerging in places.

A view of Death Valley from above Artist’s Palette shows the playa with its salt pan. A large alluvial fan is at upper left with dark inselbergs emerging in places.

The spectacular results of this ultra slow-motion collision can be seen on any canyon hike in Death Valley.  In addition, many of the rocks have been changed – metamorphosed – into a wholly different kind of rock.  The uplifted area was slowly worn down by erosion over a long, long time, eventually forming a low plain.  In other words, there were no rocks formed, in this case from the Jurassic to the Eocene, a period of 130 million years!  The missing time interval shows up as an ancient erosional surface in the rocks, what is called an unconformity.

 Unconformities are important horizons in any rock sequence, and this one shows itself in various places across Death Valley.  You can see a textbook example of an angular unconformity (the most obvious kind) in Darwin Canyon.  This canyon is about 19 miles from Panamint Springs (where you’ll ask for directions and road conditions).  It shows as a line in the rocks (surface in 3 dimensions) where layers below are at a completely different angle than those above.  In the same area is some fantastic folding.

Mesquite Flat in Death Valley National Park, California, offers great opportunity to photograph landscapes in black and white.

Mesquite Flat in Death Valley National Park, California, offers great opportunity to photograph landscapes in black and white.

THE BIG RIP

Long after the dinosaurs had disappeared, starting several million years ago, this area began to be torn apart by rifting at the edge of North America.  It’s a process that continues today.  By this time the subduction zone off the west coast had shrunk northward, where it still grinds away off the coast of Oregon and Washington.  It was replaced by the San Andreas Fault, which still marks the boundary between the North American and Pacific tectonic plates.

The lateral sliding movement of the enormous Pacific Plate moving north past the western margin of North America is essentially torquing the entire western part of North America.  It’s caused a clockwise rotation and the crust has broken into large fault block mountain ranges bounded by normal faults.  This rifting (as rifting typically does) opened pathways for lava to rise and erupt.  Throughout Death Valley you will see areas of volcanic rocks – mostly tuff (rock made from volcanic ash) and basalt (dark lava rock).  Ubehebe Crater in the north past Scotty’s Castle is just one example.

The skies above Death Valley are the playground of Navy pilots from nearby China Lake.

One of the only times you’ll look up from the stunning landscape of Death Valley is when a deep boom makes you notice the Navy jet pilots from nearby China Lake, who make the skies their playground.

 The fault-block mountains caused by rifting are Death Valley’s most obvious geological structure.  But in this far southern part of the Basin and Range, you are looking at a deeper level of rifting.  So there are not only the steep normal faults, but also low-angle “detachment” faults.  Think about the steep normal faults that border the mountain fronts curving and taking on more shallow angles as you mentally travel down their surfaces, and you have a great idea of a detachment.

Incidentally, remember the granite formed during the Mesozoic?  Go south, to Joshua Tree and other places in Southern California, and you’ll see the masses of granite all around.  This means you are seeing much deeper levels of the rifting of North America than you see in the northern Basin and Range.  Keep going and you’ll come to the Gulf of California, where the Sea of Cortez has already invaded the rift.  It’s as if a giant zipper was slowly opening, south to north along the western edge of the continent.

A black and white rendition of the simple beauty of Death Valley's sand dunes.

A black and white rendition of the simple beauty of Death Valley’s sand dunes.

 Back to detachment faults: they can cause whole mountain ranges to literally slide down a sort of shallow ramp, ending up miles from where they started.  Tucki Peak may have slid in this manner.  They really are the most efficient way to rip apart a continent!  You can see these large, low-angled surfaces where they help to form the geographic features called turtle-backs.  One such site is about 16 miles south of Badwater, where if you stop at Mormon Point and look north into the Black Mountains, you’ll notice one of these ramp-like detachment faults.

One more post coming to finish up with Death Valley, this one on the Ice Ages and the pup fish.

The golden light of a late afternoon warms the dunes at Mesquite Flat in Death Valley National Park.

The golden light of a late afternoon warms the dunes at Mesquite Flat in Death Valley National Park.

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