The annual variation between summer and winter ice cover is about 10 million square kilometers of sea ice, with around 14 million at the peak of winter cover, and a minimum that approaches 4 million late in the boreal summer. That’s a lot of variation, but that variation is the consequence of the seasons. The amount of annual variation is increasing, however: look at the light gray line for the 1980′s average: that only varied by about 8 million square kilometers of area in a six-month span. In fact, the peak winter numbers are still tightly clustered: there is less variation there than there is to the minimum summer numbers. Compare the spread of the data at the peak and the trough of this dataset. Lastly, there is a clear trend in the decadal data, showing decreasing summer ice cover of the Arctic Ocean. What’s your prediction for the minimum sea ice cover this year? What’s your prediction for the 2010′s average, as compared to the previous 3 decades?

Subscribe to Neven’s blog, and watch as the data unfurls in real time. It’s a fascinating phenomenon to watch from the comfort of your computer screen – both the natural annual variability in this remote system, and the signature of climate change that is driving the system into new territory.

Here’s an example of the brecciation:

Another thing that caught my eye at this outcrop was a lovely instance of percussion marks – the little cone-shaped fractures that form when bouncing bedload (saltating cobbles) slam into stationary outcrops of resistant rock like quartzite.  Take a look:

Can tell me which way is upstream?

A turtle, out for a stroll.

Note: I convinced my Geokittehs co-author Dana Hunter to fly from Seattle to New Hampshire to visit me for a few days. I handed in the final version of my PhD thesis on Friday May 4th, and Dana arrived the next day to help me celebrate. This is Part IV of my description of the fun georneys we had together during Dana’s visit.

Before continuing with my description of the fun georneys that Dana and I had during Dana’s recent visit, here’s a biological interlude. During a walk along a dirt road in New Hampshire, we found a turtle making his (or her?) way across the road. We stopped to take a few pictures and also to gently move the turtle off the road and out of harm’s way.

I think this is an Eastern Painted Turtle. Can anyone confirm? Does anyone know more about this turtle?

Another view of Mr. (or Ms.?) Turtle.

Frontside view.

The turtle retreated into his (or her?) shell when we went to remove him from the road.

A closer view of the turtle's shell.

I can only respond by saying that I am guilty as charged. However, while I won’t name names, I’m sure I’m not the only geologist who is guilty of being less-than-safe when rock breaking. Sometimes, it’s just too tempting to break those rocks… and you rush into breaking them without thinking of all the appropriate safety precautions. I’m extremely diligent when it comes to lab safety. I really should be more diligent when it comes to field safety.

Here’s a few rock-breaking safety reminders:

-Wear long pants. Jeans or other thick pants are excellent.

-Wear closed-toed shoes. Boots are probably best

-Wear eye protection. Safety glasses or safety sunglasses are essential. One commenter pointed out that regular old sunglasses could shatter. I personally plan to invest in a pair of safety sunglasses very soon.

-Use a rock hammer, whenever possible, especially for those particularly hard rocks. Avoid hammers that could shatter.

Okay, now who else has been a little bit lax when it comes to rock-breaking safety? Worn just regular sunglasses instead of safety sunglasses? Broken rocks in sandals? Please fess up (anonymously, if need be) so that I feel better. And so that we can all pledge to be a little bit more safe when it comes to the good science of rock breaking.

From NOAA NCDC- April 2012 was the 5th warmest April on record. Records go back 133 years.

Ocean temperatures in April were the second warmest on record and this makes April the 427th month in a row with ocean temperatures above the average of the 20th century.

Here are the exact numbers from NOAA:

From the Nat. Climate Data Center

The U.S. Climate Extremes Index was at a record high for the January April period as well:

The Climate Extremes index from NOAA NCDC.

and NOAA says for the U.S.:

• The contiguous United States mean temperature during January–April was 7.4°C (45.4°F), which is 3.0°C (5.4°F) above the long-term average and the warmest such period since national records began in 1895.

Notice how the higher latitudes are seeing the greatest departure from average temperatures. This has long been predicted as a signal of increasing levels of greenhouse gases.

Global temps. from January April 2012 were the 15th warmest on record. This in spite of the fact that a weak La Nina (colder than normal waters in the Equatorial Pacific).

This boulder is exotic to its current location. It is typical of medium- and coarser-grained diabase from the Culpeper Basin, a Triassic rift valley east of the Blue Ridge. The main minerals are plagioclase (light-colored) and pyroxene (dark colored).

This IR image of water vapor shows the Coriolis effect in action.

A great video here on the Coriolis effect by some grad students in Illinois. If you have never gotten on a playground merry-go -round and tossed or rolled a ball, you should. It’s the easiest way to see the Coriolis affect in action. Coriolis can be a concept that is a bit difficult to get your head around, but this video does a great job of explaining it.

You can see that a substantial portion of this route was above treeline, and the bit just beyond Cory Pass was indescribably epic. Just raw rock, naked and lifeless, as if it was deglaciated a week before we got there. Here’s a composite panorama view looking into the maw of Cory Pass itself:

Step across the threshold, and a gorgeous scene awaits…

I think this tower is Mt. Louis…(?)

Turning to the right, and looking down the valley… Look at those steep slopes! The phrase that pops into my mind is “sheer declivity“…

Did you spot the little character hidden in that last image? If not, I’ll zoom in on her:

As we walked down towards the bottom of this new valley (towards lunch with two marmots and a pika), we saw blocks of rock bearing multi-pronged trace fossils, which I reckon must be feeding traces:

Based on my reading of Ben Gadd’s book Canadian Rockies Geology Road Tours, I think that this is Cairn Formation dolostone – a Devonian deposit. It has a distinctly petroliferous stink to it when freshly broken – a real nostril-opener!

I’m looking forward to leading 18 NOVA students through this same hike this summer…

The view from the lair.

All good evil geologists need a  family cabin super sekrit lair. Most geologists prefer volcano lairs, but since there aren’t any volcanoes in New Hampshire, I’m making do (for now) with a lakeside lair. Once I return to my South African lair in a month or so, my geologist husband and I are going to start saving up for our volcanic island lair. Currently, I’m peacefully enjoying working very hard on some Star Trek watching, kayaking, knitting, and sunbathing world domination plotting at my lakeside geologist lair… somewhere in New Hampshire. I can’t tell you exactly where because if I do then my lair won’t be super sekrit anymore. Last weekend, my friend future empire co-leader Dana Hunter visited, and we enjoyed some geological excursions field campaigns and also spent some time watching Dr. Who planning our Geokittehs empire at the lakeside geologist lair. The view from the lair is very pretty, isn’t it?

If you haven’t already, you can read all about Dana’s holiday trip strategic planning mission:

Here on Georneys:
Georneys with Dana- Part I: Dinosaur Footprints Near Holyoke, MA
Georneys with Dana- Part II: The Rock, Fossil, & Dinosaur Shop
Georneys with Dana- Part III: The Chesterfield Gorge

Over at En Tequila Es Verdad (Dana’s blog):
“Groundbreaking result! Carnivorous Triceratops discovered…”
Geology by the Lake
Mystery Flora: Dinosaur Delights
Wuv, Twu Wuv
Saturday Song: Utah Carol
Two Women in a Boat (To Say Nothing of the Dog)

Some interesting facts I looked up regarding water:

Virtually all of that blue blob is salt water and not drinkable. Only 2.5% of that blue marble of water s fresh and 70% of that 2.5% is frozen ice in Greenland, Antarctica, or on high mountaintops. Only .007% of Earth’s water is easily accessible for humans, a fact that I made much of when taught two semesters of Environmental Science.

Without doubt, drinking water will be the story of the next century. Want some more surprising facts- go here.

The Cave of the Winds is located at the red star on the Quemazon trail at lower left.

The whole trail travels over the Bandelier Tuff (I think it’s the Tshirege Member here), towards Los Alamos Canyon. The cave itself, which seems to have been hollowed out of the tuff by natural and human activity, is a few dozen meters down from the eastern rim of the Canyon.  It’s a relatively short hike, but it gains about 400 feet (120 m) in about  1 km, so it can be steep at times. The trail itself is really beautiful, though. The trip was led by one of the members of the Pajarito Environmental Education Center (PEEC), which sponsors trial hikes of all kinds. This one was mainly about the history of the trails , but PEEC also runs geology hikes.

Looking down on Los Alamos National Laboratory from the lower part of the trail.

Looking uphill to the west. The landscape here is still recovering from the Cerro Grande fire, which happened more than a decade ago.

Looking east down the Los Alamos Canyon at the Omega Bridge (which connects the lab to the rest of the town).

Some wildflowers along the way. Everything was blooming!

The entrance to the cave. It's a steep climb down, but not too difficult; the tuff gives you lots of handholds.

The Cave of the Winds is actually very small – just one chamber that dead-ends a few dozen meters in. There doesn’t seem to have been much evidence of water here (it’s a very dry cave and there are no speleothems), so I’m guessing it’s just a crevice in the tuff that was enlarged a bit by other processes. Our guide mentioned that it was used by the campers at the Los Alamos Ranch School, and undoubtedly homesteaders and people traveling the trails here knew about it before that.

Entrance to the cave.

Don't worry, it's just a false alarm.

Not really much to see here, but it's evident that there have been cave-ins from time to time. There was quite a bit of rubble to walk over.

Once we hauled ourselves up the side of the canyon again, it was time to get moving before the afternoon rainstorms arrived. (I was quite happy to see the rain, because it meant less of a chance of wildfires. If you read about my visit last summer, you’ll remember that I’m not a fan.)

So, I didn’t quite get to the posts I was planning on, but hopefully I can reconstruct enough of my field notes to make a start of it while I’m out here. Of course, the reason I’m out here is to bury myself in some serious numerical modeling, so blogging will have to be secondary to that. We’ll see!

Then there is the political entity of Shenandoah County, which runs from Massanutten’s southeastern ridge to the West Virginia border, including the North Fork of the Shenandoah River, but not the South Fork:

Shenandoah Mountain is a ridge in Rockingham County, the next county to the southwest of Shenandoah County:

There’s also a town called Shenandoah, and it’s located on the South Fork* of the Shenandoah River, in a third county, Page, which is one of the counties** that lies between Massanutten’s southeastern ridge and the Blue Ridge mountain front:

* Note that Google Maps has mislabeled the South Fork as the “North Fork” in this screenshot. Weird. I’m not used to them making errors like that.

** The other being Warren County, home of the unwieldily-named Raymond R. “Andy” Guest, Jr. Shenandoah River State Park. Here’s a look at it:

Far from all of this, up in the city of Winchester (surrounded by Frederick County), is Shenandoah University:

Finally, of course, is Shenandoah National Park, which unlike every other place discussed so far, lies in the Blue Ridge physiographic (and geologic) province, not the Valley & Ridge:

I would argue that Shenandoah National Park is poorly named, and would have been better dubbed “Blue Ridge National Park.” While parts of it are in the Shenandoah River watershed, the river itself is nowhere within the park’s boundaries.

My wife and I are planning to move to easternmost Shenandoah County next month, to the Fort Valley (inside Massanutten Mountain). Musing on that place name got me thinking about how many other places the name “Shenandoah” has been applied to. Did I miss any?

Handwritten notes by Ernst Cloos (legendary structural geologist from Johns Hopkins University) on the area I visited last Monday on a field review of the new geologic map of the Elkton East quadrangle by Chelsea Jenkins, Chuck Bailey, Mary Cox and Grace Dawson.

The latest, genuinely remarkable, development is that Captain Maximov captured the landslide as it occurred on a video that he was shooting from the wing of the aircraft.  He has posted the video on Youtube:

You will see that the aircraft was flying orbits to allow sightseeing.  On the first orbit the slope was apparently stable, in the second it was in full collapse mode, generating huge amounts of dust.  Note the lack of an obvious triggering process (clear weather, no seismicity).  These two frames from the film arereally interesting.  This is from the first orbit, showing the site of the landslide:

And here is one from the second orbit with the landslide in full motion:

The two images are only 1 minute and 16 seconds apart, but the failure is apparently stable in the first and full developed in the second.  This is consistent with the observations from the seismic data of course, which indicates that the entire event took less than two minutes.

Colin has worked very hard to use the video to determine the location of the landslide.  The best estimate is that is was here (this is my interpretation of Colin Stark‘s great work on this, please treat is as very speculative):

This is the flank of the mountain known as Annapurna IV.

The flood event itself was very destructive.  If you have not seen in it, this video shows the wave passing downstream:

www.youtube.com/watch?v=3W0HbJRN8JE

The mechanism through which the wave was generated remains unclear.  To my mind the initial assumption that it was a landslide dam break flood seems in question given the location of the landslide.  I wonder if the slide caused extensive melting of glacial ice in the valley?  Alternative possibilities are the transition to a debris flow of the landslide mass itself, which then entrained extensively downslope, or the mobilisation of sediments in the valley.

I would be very grateful for comments and thoughts on this.  Needless to say, satellite imagery of the landslide deposit would be absolutely invaluable.

A gorgeous gorge.

Note: I convinced my Geokittehs co-author Dana Hunter to fly from Seattle to New Hampshire to visit me for a few days. I handed in the final version of my PhD thesis last Friday afternoon, and Dana arrived last Saturday to help me celebrate. This is Part III of my description of the fun georneys we had together during Dana’s visit.

After our visits to the dinosaur footprints and The Rock, Fossil, & Dinosaur Shop, Dana and I headed back to New Hampshire to our secret lakeside geologist lair. On the drive back, we stopped at the Chesterfield Gorge. Although there has recently been some illegal activitiy at the gorge, during our visit Dana and I didn’t encounter anything more dangerous than an overly friendly golden retriever who wanted head scratches. I was happy to see that the gorge is back to being a peaceful natural retreat. I think my mother’s claims of the “danger” of the gorge were perhaps somewhat exaggerated.

Gorge Trail Map. Image taken from here: http://www.tmclark.com/ChestGorgeimg-Images/CGMap.jpg

Dana and I hiked the 0.7 mile loop trail along the gorge, stopping frequently to investigate the gorge’s intriguing geology. The gorge contains a most unusual looking stream. Most of the time, the bedrock found in streams and rivers is smooth (and often covered in sediment), and the rocks found within streams and rivers are rounded. River and stream rocks are generally worn down and rounded by physical erosion caused by the passage of water over them. However, the rocks at the gorge are not very round. They generally have sharp, square edges that indicate that the stream is fairly young (or just hasn’t been in contact with this bedrock very long) since there has not been enough time for physical smoothing of the rocks.

Sharp, square edges on those gorge rocks.

More sharp, square rock edges.

More square rocks.

Dana and I made our way along the trail to the first bridge across the stream:

The first bridge. Thou shall pass.

Before crossing the first bridge, we decided to take a closer look at the gorge’s rocks. The rocks are highly-weathered, and many are covered in moss. So, we had to exercise the good science of rock-breaking:

A weathered, moss-covered rock with a freshly-broken rock on top. Penny for scale.

Unfortunately, my rock hammers and other rock-breaking supplies are all in South Africa, and Dana packed carry-on for her trip and couldn’t bring her rock hammer. So, we had to improvise a bit with the rock breaking:

Throwing one rock against another.

Rock breaking by throwing is not as effective as rock breaking by hammer, so we also gathered up some rock samples to break later. The next afternoon, we borrowed a hammer from my dad’s stash of tools and did a little more advanced rock breaking. A word of advice: in the below photos, I set a bad example. Rock breaking should ideally be done with closed-toed shoes and long pants (to prevent injury from stray rock shards), but I did remember the essential eye protection (wrap-around sunglasses, in this case).

Breaking rocks in sandals. Don't try this at home, kids!

A little more aggressive rock breaking.

Dana, breaking rocks in more sensible rock-breaking attire.

Excited about the rock-breaking results.

Here’s what we saw when we broke the gorge rocks:

Gorge rock #1.

Gorge rock #2.

Gorge rock #3.

So, what type of rock is found in the gorge? Looks like a metamorphic rock (fairly low grade) that perhaps used to be a granite or granodiorite. I managed to find a little more information about the gorge rock type by plotting the location of the Chesterfield Gorge on top of a geologic map of New Hampshire. I found the New Hampshire geologic map on the USGS website here, and I imported the map data into Google Earth. Pretty neat, huh? It’s actually quite easy to do– just download the .kml file, put it into Google Earth, and then you can look at the geologic map as Google Earth layer. Then, you can just click on a geologic formation, and an internet browser window will open with the information for that particular formation.

Below are some maps that I made in Google Earth showing the gorge location. First, here are some regular Google Earth images:

Google Earth image, showing the location of the Chesterfield Gorge in the state of New Hampshire.

A zoom-in of the previous Google Earth image.

Now, let’s take a look with the New Hampshire geologic map added as a Google Earth layer:

The geologic map for New Hampshire as a Google Earth layer. Pretty neat, huh?

A zoom-in on the geologic map, showing the location of the Chesterfield Gorge.

An even closer zoom in. The gorge parking lot area is indicated by the marker.

The marker in the above maps indicates the location of the parking area for the gorge, which is located in the orange formation. If I click on the orange layer in Google Earth, I find that the parking lot is located on the Ammonoosuc Volcanics, which is a Middle Upper Ordovician unit described as,

Part of the Central Maine Composite Terrane (Central Maine Trough) – Variably metamorphosed sedimentary and volcanic rocks of greenschist to granulite facies, locally migmatized. Area includes structural belts between the Monroe fault on the west and the Campbell Hill fault on the east; that is, the Bronson Hill anticlinorium, Piedmont allochthon, Kearsarge-central Maine synclinorium, central New Hampshire anticlinorium, and Rochester-Lebanon (Maine) antiformal synclinorium. Ammonoosuc Volcanics = 461+/-8 U/Pb per J.N. Aleinikoff, oral commun., Feb. 1994.

Since the trail to the gorge leads away from the parking area, I believe that at least part (all?) of the actual gorge is actually located in the pink layer. When I click on the pink layer in Google Earth, I find that the pink layer is Granite/Granodiorite/Tonalite of Late Ordovician Age. The unit is described as,

Part of the Oliverian Plutonic Suite (Late Ordovician) – Pink, weakly to moderately foliated, locally porphyritic biotite granitoids found in mantled gneiss domes. Mafic varieties contain hornblends. Variably metamorphosed up to amphibolite facies. Oliverian Plutonic Suite: Keene and Surry dome intrusive rocks = 444+/-8 U/Pb per NH020. Warwick dome intrusive rocks = 444+/-8 U/Pb per NH020.

So, I believe the rocks that Dana and I saw at the gorge are from the pink formation. The rocks aren’t particularly pink-colored at the gorge, but they do seem to be granites/granodiorites/tonalites (the rocks seem to contain a fair amount of plagioclase and biotite, so my guess is granodiorite although I’d really need to take a closer look, perhaps employing a thin section– any opinions based on the rock pictures?) that have been metamorphosed somewhat. I’m assuming that the ages above (based on U-Pb dating) are in millions of years, so the gorge rocks are nearly half a billion years in age. Such an old age isn’t unusual for bedrock. Nevertheless, I still find myself somewhat in awe that these rocks originally formed nearly half a billion years ago. What history is exposed in the gorge!  As a quick aside, when people ask me why I became a geologist, I sometimes say, “Well, I always liked history. And geology is really ultimate history, if you think about it. Geology is the study of the history of our planet– and other planets and planetary bodies.”

So, why do such old rocks host such a young stream? Clearly, the stream hasn’t been in contact with the bedrock very long or else the metamorphic gorge rocks would be worn smooth. I searched and searched for some academic papers on the formation of the Chesterfield Gorge. However, despite spending quite a bit of time using search tools such as GeoRef and Google Scholar, I didn’t find any scientific papers on the gorge. If anyone knows of any publications on the gorge’s geology, I would be most grateful if you would direct me to them. I couldn’t even find the gorge in my Roadside Geology of Vermont and New Hampshire book.

The best information I could find on the gorge’s origin is a PDF of an information pamphlet published by New Hampshire State Parks. The brochure indicates that the gorge is located along a fault (I’d love to bring Callan to the gorge to take a look at the structural geology) and that Wilde Brook (never knew the stream was called that until I read this brochure) is a superimposed stream that originated from glacial meltwater ~12,000 years ago. The sediment and gravel that once covered the metamorphic bedrock have been eroded by the young stream (I presume 12,000 years is fairly young for a stream? Perhaps not?), and now the metamorphic bedrock is slowly being eroded.

There is certainly some evidence that there was once a retreating glacier in the Chesterfield Gorge area. For example, just look at this enormous glacial erratic:

A glacial erratic boulder, just a few feet from Wilde Brook.

After Dana and I spent some time breaking rocks at the first bridge, we made our way down to the second bridge. Along the way, we saw some beautiful scenery:

Gorgeous gorge scenery.

More gorgeous gorge scenery.

After a short hike, we found ourselves at the second bridge. When we arrived, we found that we had a slight problem:

The second bridge. Thou shall not pass.

Since we are intrepid geologists, we decided to ford the stream rather than backtrack:

Venturing off the beaten path.

Caulking the wagon and floating didn't seem necessary.

Dana looked a little nervous before the stream crossing, but she made it just fine.

After fording the stream, we headed back up towards the parking area. On our way out, we had another look at the first bridge:

Peaceful and pretty.

And we also found some interesting biologically-assisted rock erosion:

Tree root style rock erosion.

More tree root style rock erosion.

And we saw some interesting mushrooms:

Pretty fungi.

And we found a tree growing in a neat shape:

Strangely shaped tree, with geologist for scale.

All in all, Dana and I had a good day of geologizing. We saw dinosaur footprints, visited a kitschy rock shop, and explored the geology of a gorge. After this full day, we picked up a pizza and headed back to our lakeside geology lair to watch Dr. Who. Next up: Day 2 of our georneys!

The "Supermoon" of March 19, 2011 (right), compared to a rather "average" moon of December 20, 2010 (left): note the size difference. Images by Marco Langbroek.

You may have heard all the excitement last weekend about the so-called “supermoon”. The gist of it is that the moon’s orbit is not perfectly circular, so its distance from the earth varies slightly. When it is at the closest point in its orbit, it looks slightly larger (and therefore slightly brighter) in the sky. It’s not really a big deal, and all the talk of the SuperMoon got many astronomers worked up in much the same way we get worked up about the Mars Hoax or the 2012 doomsday.

But all the talk of the “SuperMoon” got me thinking and I realized that we were missing a teachable moment. No, the moon being at perihelion is not a big deal, but our Moon is pretty “super”. Let me show you why:

When you look at the mass of the largest moons in the solar system relative to their planets, our moon really stands out. In fact, most of the bars on this chart aren’t even visible because the moons are so tiny compared to their planets. To see them, we have to switch to a logarithmic scale (meaning each step on the vertical axis is 10 times larger than the previous step).

There, now we can at least see some of the other large moons. Phobos and Deimos are still off the chart because they are just tiny captured asteroids, dwarfed even by the relatively small mass of Mars. Likewise, other than Neptune’s giant moon Triton (which may actually be a captured Kuiper Belt object) its other moons are tiny.

Of course, our moon is physically smaller than the big moons in the outer solar system, but because the gas giants are so large, their moons are smaller in a relative sense. This difference points to a difference in how the moons formed. Whereas most of the big moons around the outer planets formed out of the accretion disks for their planets, our Moon formed when the proto-Earth was whacked by a giant impactor about the size of Mars, ripping off a huge chunk of material that ended up coalescing as our Moon.

So, out of all the planets, our moon is the largest relative to its planet. Of course, if Pluto was still counted as a planet, its moon Charon would hold that title. Charon is so big that the center of mass of the Pluto-Charon system is outside of Pluto, leading some people to call Pluto-Charon a “double planet”.

Now I’m looking forward to next year’s “super moon” so I can (a) tell them that the moon being a little closer isn’t that big a deal, and (b) I can tell them why we really do have a super moon.

(click on the image to get to a larger sized version on Max’s Flickr page)

That’s the Warah Formation exposed on the Batain Coast of northeastern Oman. This is the thrust front of a thin-skinned fold and thrust belt. I think it’s just lovely!

Max has a ton of other great structure photos on Flickr, he tweets, and he has a blog. Check out his work!

Immediately after lunch, we visited an outcrop in the middle of Naked Creek. You’ll be happy to hear that we all retained our full complement of clothing there. But the rocks were hardly brazen and revealing, either. At first glance, it looked like relatively massive quartzite.

This is the same outcrop where we saw one of the three snakes that the field trip brought us into contact with. The geologists spread out and got up close and personal with the quartz sandstone there…

…We found that if you looked closely, there were some subtle clues that made the outcrop make sense…

Those are Skolithos: trace fossils oriented perpendicular to bedding. They are very common in the Cambrian-aged Antietam Formation, a quartz sandstone that has seen some noticeable deformation.

Since Skolithos are perpendicular to bedding, that allowed us to deduce the orientation of the primary sedimentary layering, and compare it to a widely-distributed cleavage which dipped to the southeast. Overall, the outcrop looked roughly like this in map view:

Just one outcrop among hundreds that went into the map…

On 5th May 2012 the global seismic network detected what appeared to be a landslide event to the north of the town of Pokhara in Nepal.  Soon after a flood wave travelled down the Seti River, killing over 50 people.  It is likely that the wave was triggered by the collapse of a large landslide mass that had impounded the river.

Colin and Goran have now undertaken Landslide Force History (LFH) inversion for the event that they detected on 5th May, and to quote Colin (with his permission) “we are now 100% sure there was indeed a seismogenic slope failure in the Pokhara area”.

Their best estimate for the landslide parameters are as follows:

1. Date/time: 5th May 2012 at 03:24:56 GMT = (i.e. 09:09:56 local time)
2. Runout duration: ~103 seconds
3. Max force: ~1.2*10^11 N assuming a mass of 1.4*10^11 kg (see note#1 below)
4. Runout distance: ~1040 m (see note#1 below)
5. Height drop: ~350 m (see note#2 below)
6. Max accel: ~0.85 m/s^2 (depends on mass assumption)
7. Max speed: ~24 m/s (ibid)

Colin notes that:

Note#1: There is an inherent ambiguity in the LFH inversion since we obtain force, which is mass*acceleration, which integrates up to mass*distance. If we specify mass, we predict runout distance (and height drop); if we specify runout distance or height drop, we predict mass. In this case I would bracket (generously) thusly:

1. n/c
2. n/c
3. n/c
4. Mass range: 5*10^10 kg — 2*10^11 kg
5. Runout distance ~ 2910 m — 740 m
6. Height drop ~970 m — 250 m (see note#2 below)
7. Max accel ~ 2.4–0.6 m/s^2 (depends on mass assumption)
8. Max speed ~ 67–17 m/s (ibid)

From experience I would guess somewhere in the middle is most likely, i.e., my guess above at a mass of around 1-2*10^11kg. Once we have satellite imagery, the bracketing will improve markedly.

Note#2: The inferred height drop is dependent on the mass assumption (or measurement), but it is apparently also dependent on slope failure mechanism – on occasion, we appear to underestimate (in the LFH inversion) the vertical force involved. This may simply be because our inversion scheme does not at present apply extra geomorphic constraints beyond the requirement of net stationarity. We’re working on this.

One of the most intriguing aspects of this technique is that it generates a trajectory of the centre of mass of the landslide.  This is a planform diagram in which the length of the arrow indicates the relative speed:

One very useful result: the planform trajectory of the landslide center of mass. Here’s a pic (the arrow size gives relative speed):

Thus, as Colin says:

“This landslide (centre of mass) moved almost directly westwards with a modest bend in its trajectory”

So, assuming that the detected event did provide the debris that triggered the collapse, where did it happen?  Well, the analysis of the data suggests that it was in this area, althoigh it is not well constrained:

From there we can turn to the second amazing part of this story.  Kunda Dixit is a well-known journalist in Nepal.  A day or so ago he made the following comment on this blog:

The latest death toll is 17 dead 47 missing. The cause was neither glacial lake outburst nor ice avalanche but the collapse of a rockface on the eastern flank of Machapuchre.

You may find these interesting:
http://nepalitimes.com.np/blogs/kundadixit/2012/05/05/avalanche-flood-on-seti/
and
http://nepalitimes.com.np/blogs/kundadixit/2012/05/05/eye-in-the-sky/

Machapuchere is shown in the image above.  However, the landslide moved from east to west, which suggests that it was perhaps a failure on the rockface downstream from Annapurna II.  Note though this is just speculation at this time, and it could of course be that the landslide event that was detected and the event that caused the flood are unrelated (although the coincidence would be surprising).

Finally, it is worth noting that Kunda Dixit’s post points out that the alarm about this flood was raised by a light aircraft pilot, Captain Alexander Maximov, who saw it from his aircraft.  There are even images of the front of the flow taken from the aircraft:

http://nepalitimes.com.np/blogs/kundadixit/wp-content/uploads/2012/05/5.jpg

It had flattened its head to make it very spade-shaped. The right eye was cloudy – perhaps snake glaucoma? Or maybe it was just getting ready to shed its skin?