Sierra Nevada Mountains Age: Continuing Growth Fuels Geologists' Debate

By: Crystal Gammon, OurAmazingPlanet Contributor
Published: 05/04/2012 12:27 PM EDT on OurAmazingPlanet

If it's true that a lady never reveals her age, then the Sierra Nevada mountain range, with its rich wilderness and snow-capped peaks rising above California and Nevada, is quite the lady. Researchers still don't know exactly how or when those rocky summits got there.

Now, new research has uncovered a clue in this geologic puzzle. Using GPS and space radar technology, scientists found that the range — which includes Lake Tahoe and the highest peak in the contiguous United States, the 14,505-foot-tall (4,421 meters) Mount Whitney — is growing by about a millimeter each year. At this rate, the entire Sierra Nevada could have been built in just the last 3 million years, the researchers say.

"There's a surprisingly wide variety of opinions about how and why the Sierra Nevada goes up, and about the ages and timing of all the events that contribute to the uplift," said William Hammond, a geophysicist at the University of Nevada, Reno, who led the study. "These findings suggest that whatever mechanism is at play, it's acting on the entire range."

An age-old question

Geologists say there are two possible, and wildly different, ages for the Sierra Nevada range: either 40 million to 80 million years old, or only about 3 million years old. [50 Amazing Facts About Earth]

That's a big difference, Hammond said, because it means the mountains are either very old and no longer growing, or they're quite young and still growing at a measurable rate.

To figure out the Sierra Nevada's current growth rate, Hammond's team combined GPS data with measurements from interferometric synthetic aperture radar, or "InSAR," a type of space radar.

In this radar technique, a satellite whizzes over the Earth and uses microwave energy to take snapshots of features like mountain ranges and earthquake faults. The satellite then revisits the same spot every month or so to take more microwave snapshots. Because it can monitor large swaths of landscape over long periods of time, InSAR data is particularly useful for measuring slow and steady changes in the shape of the Earth's surface.

"Most of the seismic cycle is made up of periods of time where the Earth is not shaking, but it is deforming," Hammond told OurAmazingPlanet. "We're getting better at measuring that slow shape change as a way of understanding, for example, where the Earth might break in future earthquakes."

His team analyzed 18 years of Sierra Nevada InSAR images, along with precise measurements from GPS stations, to zero in on a growth rate of about 0.04 to 0.08 inches (1-2 millimeters) per year for the mountains.

This means the entire range, which has an average high elevation of about 6,500 to 8,200 feet (2,000 to 2,500 meters), could have been built in less than 3 million years.

How did the mountains get there?

Exactly how the Sierra Nevada range was built is still a mystery, though, and theories abound.

The mountains lie just west of the Basin and Range Province in Nevada, where east-west tectonic forces are in the process of ripping the Earth's crust apart. Some geologists think this stretching might be causing the eastern side of the Sierra Nevada to grow upwards.

Another idea comes from seismologists, who believe they see a weighty blob in the Earth's mantle that may have been attached to the base of the Sierra Nevada tectonic block. They think this dense blob used to weigh the block down, like a keel on the bottom of a ship. Then, sometime between 3 million and 10 million years ago, this keel peeled off and sank down deeper into the Earth, and the Sierra Nevada block popped up.

Whichever it was, Hammond's team found that the process affected nearly the entire range — from Lake Tahoe to the Mojave Desert — and is still building up the Sierra Nevada today.

The team's findings were published on April 27 in the journal Geology.

• The World's Tallest Mountains
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• Earth Quiz: Mysteries of the Blue Marble

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Comments

[MzKimi2U]

06:28 PM on 06/18/2012

The Sierra Nevada Mountains are very beautiful and I love being able to look out my window and see them. I also love spending my summers at Lake Tahoe, the whole mountain range is magnificent.

[AndKoolaidForAll]

05:53 PM on 05/09/2012

Yellowstone is still the uplift winner on North America, hands down, lifting as much as 2.7 inches per year, some years, since 2004. Of course, nobody's really seems concerned the Sierra Nevada Range could go up like 10,000 Mt. St. Helens - tomorrow, and destroy most of OUR country...

http://news.nationalgeographic.com/news/2011/01/110119-yellowstone-park-supervolcano-eruption-magma-science/

[ceekreewd]

02:49 PM on 05/08/2012

If the measurements were more then 1/2 inch of rise per year -- that's something to take notice of...but 1 mm per year...come on, the reasons for that tiny amount could be the results of MANY geological activities that have absolutly nothing to do with mountain growth ! A millimeter...come on.

[Pat Snelling]

10:45 AM on 05/07/2012

Drive from Sacramento to San Francisco.... You can see the whole "coastal" Mountain.... Now drive from San Francisco to Sacramento and you see ONLY the TOP of the "Sierra" Mountains.....

It's like driving up a slope.... We've been told half of California is going to fall in the ocean... The San Francisco half.... I'll sure miss it..

[Jayjaybe]

02:04 AM on 05/10/2012

"We've been told half of California is going to fall in the ocean... " No knowledgeable person would tell you such a thing, especially since the direction of tectonic plate motion is inland. California can't "fall" into the ocean. It's moving toward Las Vegas.

[MzKimi2U]

06:27 PM on 06/18/2012

Most of California is resting on a fault line. If a big enough quake strikes, the side of the fault line on the west will fall into the ocean as most of California is more or less a shelf, same as Florida.

[teecee656]

09:56 PM on 05/14/2012

The San Andreas fault divides the pacific plate thats moving northwest and the continental plate. In a few million years Los Angeles and San Francisco might be neighbors, and you'll be able to commute from San Diego. Don't worry though, by then probably both Yellowstone and the Long Valley Caldera in the Eastern Sierra, the only two super-volcanos on the continent will have erupted and mankind will probably be extinct.

[FreewheelinFranklin]

05:07 AM on 05/07/2012

Awww, that's nuttin'. There's a mountain on the other side of the county where I live that grows several hundred feet each year. Soon it will be taller than the Sierras. It's affectionately known as Mount Basura.

[SnapShots]

02:32 AM on 05/07/2012

This article is very puzzling because it is contradictory to what geologists have deduced for decades. That deduction is the Pacific plate used to move east and subduct beneath the North American plate, pulling continental material down with it. That plate boundary allowed heat from the mantle to reach the surface, creating volcanoes. As the collision of the Pacific and North American plates changed to lateral movement (north/south, think of San Andreas fault), the subduction stopped as did the volcanic activity. The large seas of molten lava beneath were batholiths, which cooled slowly, allowing minerals to form within the rocks, which is what we know as granite. The cooled batholiths, being lighter than the denser mantle material in which they floated, began rising as the dead volcanoes above them were eroded away. Volcanoes eroded away and the granite rose from beneath in their place, also bringing up continental material that had subducted. This is why we find sea shells at the tops of some mountains in California, particularly the coastal ranges. http://www.ucmp.berkeley.edu/science/profiles/erwin_0609geology.php

[Wanderland]

12:15 PM on 05/07/2012

When you say "deduced for decades," what you really mean is that there was a working theory in place. But western geology is very complex, and there are a lot of unknowns that have theories explaining them, but the theories are regularly altered or changed as additional evidence is found.

[SnapShots]

12:33 PM on 05/07/2012

Yes, theories change, but for them now to say that the origin if the Sierra Nevada is a complete mystery is baffling.

[Jayjaybe]

03:38 PM on 05/09/2012

This article is an oversimplication that's based more on the lack of knowledge by the writer than the state of the science. Decades of on-the-ground studies are misrepresented by omission. The Sierra Nevada are one of the most studied ranges in the world. They are located in a complex tectonic terrane in the most populous state in the nation. California is so geologically challenging to study that the USGS has ceded most of the investigative study to the California Geological Survey which virtually served as a model for and contributed to spawning the USGS. The thought about competing theories is a flat concept of the scientific method. The merged complexities of the scientific models of the geologic history of the Sierra Nevada are generations beyond the "competing theories" nonsense.

[galactictravelerjavjav]

01:07 PM on 05/06/2012

I reached out and touched it!! Then it wore off and went to bed.

[Bradley Scott Roon]

11:08 AM on 05/06/2012

Unintentionally a very funny article. Don't know "exactly" how old they are? Well, can you say Duhhh? Were you there either 3 million or 80 million years ago to see them start? Friday the forty - twoth of the Season Krabnuzhgar. That's when they started.
Long term pictures of change from a new technology and new application of that? Millions of years old and we've been looking for how many decades, if that?
The mountain ranges couldn't have started growing and then had plate subsidence or periods of inactivity and then built again later? Is there some proof or indication that mountains grow consistently instead of intermittently?
This is such pseudoscience, but "technology" and "science" are the new (sigh) religion.

[Riverman]

12:54 PM on 05/06/2012

News media do not handle scientific reporting well at all. However the pursuit of knowledge by applying the scientific method of gathering facts and testing ideas is in no way related to believing in fairy tails. As this article makes clear science makes no pretense of knowing everything where as religions all both pretend to know everything and that their "special" knowledge comes from magical invisible beings and creatures.

[Bradley Scott Roon]

11:37 PM on 05/06/2012

I was amused to read a poster recently on a friend's fb page. He is a confirmed atheist and in response to a post he had the poster about the "Christianity is where a Jewish zombie" blah, blah, blah.
The day after reading that i was even more amused to see a similar poster which basically stated that scientists believe that in the beginning there was nothing. Then nothing happened and suddenly somehow for no reason there was everything and by random mistakes there were suddenly dinosaurs and things like that.
Unlike this poor recall it was very funny.
I do find science firmly stating things they have no way of knowing. I also find rabid Darwinian evolutionists maintaining that Darwinian evolution is a "proven fact" when according to D, the evolution was consistently slow, steady, gradual, and upward. What we see is a foot ball field in which things are very slow, then basically stagnant, then at the 82 yard line everything happens. BAM.
Not gradual, slow, steady, consistent. Does it totally invalidate evolution? Of course not. Darwin's slow steady hypothesis? Deader than a doornail. (which is a hand forged square nail, usually with a rose head and the bottom which pierces the wood is bent over and pounded into the wood.) That dead.

[Bradley Scott Roon]

10:30 PM on 05/07/2012

No ability to reply to your last post.

Man, i came on in a somewhat sardonic mood to make fun of the article and the assumption that flawed beings could EXACTLY know how old the mountains are, as if that really matters. They are here now. So am i. Are you?

Suddenly, i am assumed to be a "Christian" or religious person, and this assumption includes my apparently having an agenda of ignorance! What a trip you have taken on the thoughts (never enough room to adequately express deeper concepts) you THINK i have. Very interesting.
Like Freud, it seems to show more about you than about I. Have i told anyone don't believe in science? No i point out a few scientific inadequacies, inadequacies which are inherent in ALL human functions since by definition we do not know everything. We can't see everything or understand everything.
One little example is the carbon atom. When talking to Scott Dixon, electrical physicist and holder of numerous patents in the field, he pointed out that the physical portions of a carbon atom are one part volume in Five Hundred Trillion parts, and those 500 Trillion volume "spaces" are essentially unknowable to an extremely great degree. Imperfect senses, and we don't know what is going on in that unknowable portion to state ANYTHING definitively.

[DrTachyon]

04:52 PM on 05/06/2012

You are repeating a commonly held fallacy the somehow events are unknowable if not witnessed directly. For just one example, we know Pluto takes a little over 200 years to orbit the Sun, yet no human has ever witnessed it; it was only discovered in the 1930's. In fact, Pluto is bloody difficult to see at all and we know far less about it than we do about the Sierra Nevadas. The question addressed in the article is far more difficult the calculating Pluto's orbit, but using your reasoning, understanding bith are somehow beyond us? Which is strange because you rely on trusting you interpretation of the evidence for past events every day. Most often on data even more flimsy than that for growth of these mountains.

[CyclingKen]

11:07 AM on 05/06/2012

Yeah, I think it's growing even faster than a millimeter per year. I hike the same mountain every year (near Tahoe/Fallen Leaf Lake) and it gets several feet higher each year. Either than or I'm getting older.

[j l mcdonald]

08:37 AM on 05/07/2012

What I can't figure out is how the trails can be consistently uphill both ways.

[Wanderland]

12:19 PM on 05/07/2012

And why, when I was in my 20s, was going downhill so much easier than going uphill? Seems to be completely the opposite today.

[WorkhelpWorkhelp]

01:48 AM on 05/08/2012

That's what my grandma used to tell me. Had to walk to school in six feet of snow, in the dark, and uphill. Both ways!

[Llib Noswad]

09:07 AM on 05/06/2012

3 million years? A millimeter a year? I don't think so, I'm 69 years old and I don't even remember them being there when I was born. They're growing a lot faster than the scientists think.

[TheyCallMeLtKelso]

02:36 PM on 05/06/2012

Have you ever seen the Sierra Nevada Mountains?

[Llib Noswad]

07:58 PM on 05/06/2012

Yeah, I've watched them grow.

[mamacat]

05:30 AM on 05/06/2012

When I was a youth the given altitude of Mt. Whitney was less than 14,500 feet. Now they say it is 14, 505. Part of that is due to more accurate measurements, but part of the difference is due to the continual uplift of the mountain: if it is going up at over 1 millimeter per year, or about 1 inch every 20 years, then that would explain part of the difference in altitudes since the last century.

[rt1027]

10:25 AM on 05/06/2012

it is cool though

[Jayjaybe]

10:08 PM on 05/06/2012

You state much of your own answer. We only really have modern accuracy in modern measurements. The amount of error in measurements in 1960 could leave you with only a guess, an error bar. But, changes in rates over geologic time would be more interesting. So much tectonic plate boundary migration has occurred from the western direction, as is still involved with the San Andreas Fault Zone, that some variations in the orogenic processes, and their rates, are clearly not represented in the short-term studies in this article. The local park rangers in the various National Parks of the Sierra Nevada have been presenting much better information for decades.

[ruckas356]

09:52 PM on 05/05/2012

how the hell can they messure that its growing a millimeter every year? cmon now

[caution50]

10:28 PM on 05/05/2012

InSAR is a method of combining multiple radar images to constrain surface deformation over a period of time. It's extremely accurate, to the centimeter. The "millimeter per year" growth rate is an average, not a continuous rate. The surface will remain static for years, then shift in fits and starts.

[afgail]

08:25 PM on 05/06/2012

Could just be that the Sierras are being pushed up and riding over a subduction eastern edge of the Pacific plate.

[TeebagsKiLLingAMERICA]

12:42 AM on 05/06/2012

Calculus and laser images are used. Most people use neither of these ever.
If they found a moon-base on the dark side of the MOON, or Life proof on Mars, WOULD YOU BELIEVE THEM ?

[robodawa]

08:29 PM on 05/05/2012

Is there a limit to the height a terran mountain range can attain?

[pagangrandma]

10:31 PM on 05/05/2012

Theoretically, no, but erosion wears away the mountain range at the same time it's growing. It depends on the rate at which these two things are happening, relative to each other, that determines whether the mountains are growing, shrinking, or staying in equalibrium at any given time. Eventually though, erosion will win out, and wear the mountain flat.

[blackwind]

12:57 AM on 05/06/2012

And along with erosion, plastic deformation of the basement rocks due to the weight of the overlying range will also slowly lower mountains higher than a couple miles high too. I heard somebody suggest that mountains on earth have probably never gotten much, if any, higher than the Himalayas because of that effect.

[Jayjaybe]

01:20 AM on 05/06/2012

One addendum is that the orogenic processes differ. In some mountain building, the upthrust is moderate enough to allow erosive processes to have comparatively telling results over given time periods, depending on the bulk rock properties. In other regions, such as the Andes or the Himalayas, tectonic processes are contributing much more uplift than erosive rates can oppose over comparable time periods. The modern Sierra Nevada aren't presently involved in a strong crustal uplift regime. However, the Himalayas are products of the ongoing headon collision of the Indian Plate with the Eurasian Plate. This uplift has happened at a faster rate than is happening with the Sierra Nevada. There are oceanic sedimentary rocks near the upper portions of Mt. Everest that are much younger than the rocks along the Sierran crest. But essentially, grandma's spot on.

[caution50]

10:32 PM on 05/05/2012

Interesting question. One of the newer fields in geology studies just those limits that you are talking about. There seems to be a relationship to the height of a mountain range an its erosion rate. The higher the range, the greater the steepness of the slopes, and the faster it erodes. So height does seem to be limited in part by, of all things, climate.

[blackwind]

01:03 AM on 05/06/2012

And to add another, lesser known, layer of complication, the rapid erosion in the valleys of a high mountain range can remove enough weight quick enough to cause the whole range to rise. So erosion can make mountains higher!

[OC Surfer]

06:50 PM on 05/05/2012

The Sierra Nevadas were created so that we could have Yosemite. God lives in Yosemite.

[ruckas356]

09:54 PM on 05/05/2012

The sierra nevadas were made to give life to Yosemite Sam, i say i say i say how could you disagree??

[TeebagsKiLLingAMERICA]

12:45 AM on 05/06/2012

God lives in ALL THINGS. Spirits are more concentrated in some areas and less in others by natural Law.

[RedRat]

05:53 PM on 05/05/2012

Another plausible explanation is that the growth of the mountains is not constant, but the mountain range is moved by slips and starts, basically a jolting process. It just might be that the growth we see here, about 1 mm per year is just the current rate for the past decade or so. These processes take millions and millions of years. Could be that the basic thrust occurred many, many millions of years ago, then stopped, then started again. We know that this happens in subduction zones, they hang up and then break loose, sometimes with a snap.

[nasknit]

11:46 PM on 05/05/2012

Thank you. I can't understand people who think that the current speed of anything, means that it is a constant speed.

[RedRat]

12:56 PM on 05/06/2012

Agreed. Far too many people believe that the current snapshot represents all time. In reality, this snapshot is statistically meaningless when the millions of years are sampled. Some of us are doomed to be scientists I guess and look for other explanations.

[Jayjaybe]

01:26 AM on 05/06/2012

Actually, this article's perspective is overly simplistic. Down on the ground, generations of field studies have found that this is at least the 2nd generation of the Sierra Nevada. The renown "roof pendants", strewn throughout the range, are relicts of a previous generation. At some locations, park rangers include this info in their daily presentations.

[RedRat]

12:59 PM on 05/06/2012

I thought as much. Though I am not a geologist by training, I have enough interest to have read a bit about the Sierra Nevada range. Basically, it appears from maps and satellite images to be a "crumple" zone due to the tectonic activities in California and all along the west coast. In reality, we also have "fast" movement up here in Washington State out on the Olympic Peninsula of about the same rate. Between the Pacific plate and Juan de Fuca plate out here, this is a pretty active area.