Perseids

Continuing an astronomical theme, here’s a short video of the Perseid meteor shower. I took it from Lake Mary and saw 55 meteors during the couple of hours I was filming, but it’s hard to get them to show up on a digital camera so there are only about ten visible here (and then only if you watch it in fullscreen HD). Eventually the moon rose and weakened the viewing (it was a bit misty down by the lake), so I had a good excuse to go home to bed.

Eclipse hat-trick!

Our solar system is SO busy at the moment! Three ‘eclipses’ in just a few days, starting with the annular eclipse of the Sun, then a partial eclipse of the Moon, and right this minute the transit of Venus. This is for my soggy, cloud-covered British chums!

Annular Eclipse, Grand Canyon

The track of yesterday’s annular eclipse crossed just north of here, and for the first time in my life I was in a place with guaranteed clear skies, so I went to the Grand Canyon to look at it.

Of course, so did a few other people…

Some with fancier equipment than others

The sun’s only 93,000,000 miles away. How big a lens do you need?

First contact. (BTW, my lens isn’t dirty – the smudges are sunspots)

Our ‘Scope of the Month’ Centerfold

But my little camera and a piece of welder’s glass did me proud

Not everyone needed a telescope

Without a filter it was pretty hopeless

So trying to get the scenery in just made it look like a normal day

But it was still partial at sunset, so finally I managed to get a shot of sun and canyon together

Everybody has their faults – here are some of mine

One of the many things I adore about rock is the way it offers such a joyous sense of perspective. When I realize what a tiny blip in geological history I am, most of my troubles start to look pretty pathetic. After all, even the entire history of mankind will one day be reduced to a small brown stain in a few cliff faces. And yet, at the very same time, rocks make me feel wonderfully connected to everything that is and ever was, and I become acutely aware of the meaningful part I play in this huge and beautiful story. It’s quite paradoxical.

The other day I needed to go out for a walk to do some thinking about the brain, so I decided to stroll along the Lake Mary Fault, a few miles from my apartment. Lake Mary lies in a Graben – a block of the earth’s crust that has slumped downwards between two faults. The fault line itself is pretty dull to look at and yet, as my mother often used to reassure me, looks aren’t everything:

Part of the Lake Mary Fault. I said it wasn't much to look at!

 

Actually, the other side of the lake – the Anderson Mesa fault – looks rather more dramatic, but the point is that Lake Mary is on a pretty big chunk of rock that’s slipped down between two cracks. For much of geological history, the land that is now Arizona was being squished together like a concertina by unbelievable tectonic forces. That’s why the rocks beneath my feet contain fossil sea shells when I’m actually 7,000 feet above sea level. Back in Permian times these rocks were forming on the sea bed, but since then the entire Colorado Plateau has been lifted up by at least a mile and a half, as the oceanic crust of what’s now the Pacific inexorably buried itself under the continent like a cat trying to hide under a rug. The majestic Rocky Mountains owe their existence to such squishing but, as it turned out, this was merely a petulant phase this part of the planet was going through. In more recent times, relatively speaking, the forces acting on Arizona have been in the opposite direction, pulling the state apart again like books slumping on a giant bookshelf after nature took away the bookends. The Lake Mary Graben is one of the smaller pieces of evidence for this stretching.

So anyway, I was merrily wandering along this fault-line and I suddenly remembered that local geologists are predicting a significant earthquake on this fault, sometime in the next decade or two. I whipped out my trusty iPhone and looked to see how much the fault is actually moving (there’s an app for everything these days). I admit I was kind of hoping the earthquake might happen that morning, since I was in the perfect place to watch it. The answer, though, much to my disappointment, was that the fault is currently slipping by no more than 0.2mm per year.

0.2mm? That’s not even as thick as my fingernail! Admittedly, if we are expecting a magnitude 6.9 earthquake soon then there must be a lot of pent-up energy waiting to be released, and in a photo below you can see some blistered rock along the Anderson Mesa fault that gives a hint of this tension. But 0.2mm is pathetic! It occurred to me that I’d have to wait five years just to see a single millimetre of movement.

Come to that, it means there’s only been a centimetre of slip in my entire lifetime. Less than the width of a fingertip.

Five hundred long years ago, back in 1512, when Martin Luther was receiving his doctorate and the ceiling of the Sistine Chapel was first being shown to the public, the lake was thus a mere ten centimetres higher than it is today. In order to get to a whole metre of slip – the distance from my outstretched fingertip to my nose, I’d have to go back, not five hundred but five thousand years, to when Stonehenge was being built and the Bronze Age was just getting underway. Multiplying by ten once more takes us back to a time long before the last glaciation, when the first people were just begininng to wander into North America from Siberia and a small asteroid the size of a parking lot was hurtling towards the planet, intent on creating Meteor Crater, which is not very far from Lake Mary. All of this happened just ten metres of fault movement ago; the height of a house.

Fracture in the Anderson Mesa fault zone, showing there's tension in the rock

 

Standing there on the shore of the lake, looking up to the top of Anderson Mesa, where I often go running, I suddenly felt rather small. Once upon a time, a very long time ago, the land I was currently standing on was all the way up THERE. Having huffed and puffed my way up that hill at this altitude I can tell you that it’s a great deal more than ten metres to the top, so we’re talking about many times greater than 50,000 years of movement.

Of course extrapolating from today’s 0.2mm per year any further than a metre is pretty silly. It’s like saying “if present trends continue, that tree will be ten miles tall by the end of the millennium.” Present trends rarely do actually continue, and that’s certainly true for earthquake faults. But just to keep the metaphor running, let’s multiply by ten yet another time. Now we have a hundred metres of hypothetical fault movement, which is about the distance the crust under Lake Mary has actually slumped since the earth around here first cracked. This takes us back half a million years into the past. At 0.2mm per year to create a hundred metres of movement this seems such a crazy long time ago, but half a million years is only yesterday in geological terms. In fact it used to be called the Recent Epoch. That’s like, last Tuesday!

Our increasingly absurd fault analogy will give us a kilometre of earth movement after five million years. That takes us to the beginning of the Pliocene.  If we were to go back in a handy time machine, life wouldn’t look all that unusual. There would be Mastodons instead of elephants, but camels and armadillos looked pretty much the same then as they do today, and it wouldn’t be all that long before Australopithecines were wandering around Africa, tantalisingly leaving their bones behind to perplex future anthropologists. A kilometre of vertical movement along the fault isn’t actually possible at Lake Mary but it’s not at all unreasonable for faults in general. Many faults in Arizona have more than a kilometre of throw. Don’t forget that Lake Mary is itself two kilometres above the sea in which its bedrock originally formed and there was probably a good deal more rock above this point before it eroded.

Multiply by ten one more time and we reach back to fifty million years ago and a completely hypothetical ten kilometres of crustal movement – about the distance between here and the post office, traveling at a rate not much greater than the size of the period at the end of this sentence each year. Pause here for a moment and just think about that last sentence. Imagine someone setting out to post a letter and yet, a whole year later, their car has only moved by the width of a full stop. But after all these powers of ten we still haven’t even got back as far as the last possible moment in which to see dinosaurs (if you don’t count chickens).

It’s in the nature of powers of ten that they rise pretty rapidly, so including another power of ten actually skips most of the interesting stuff and lands us right in the middle of the Cambrian period, half a billion years ago. I was once lucky enough to stand on the famous Burgess Shale in British Columbia and hold in my hand some of the freaky alien animals that lived during this period but whose descendents never made it to our time. Of course, I couldn’t have stood near Lake Mary and done the same thing, since the rocks on which the lake now rests wouldn’t form for another 250,000,000 years.

One final power of ten and we get back to five billion years. Now we’re talking serious time. The earth didn’t even exist yet and nor did our sun. According to some scientists, we only have another five billion years left before the universe ends, so I guess I’d better stop with this fanciful analogy while I still have time. But my point is, a fault that slips one puny fifth of a millimetre per year really brought it home to me how astoundingly ancient this planet is. Some days I feel really old, but heck, my entire lifetime accounts for just a finger’s width of movement along the Lake Mary fault. And that’s considered “active.”

Major fault near the Verde Valley. Notice how the rocks on the very left of the picture bear no resemblance to those on the right, showing how far this side has slipped downwards. Hundreds of metres of rock have been eroded from above the right side of the fault.

 

The general point I wanted to make is that standing on any old lump of rock, as long as you have some idea what you’re actually looking at, really puts life into perspective. In a way it makes me feel very, very, very small. The forces that shaped Lake Mary and raised the Permian sea bed over a mile into the air, and the fact that the fossil sea shells I picked up that morning last drew breath a quarter of a billion years before human beings were even thought of, puts me right in my place.

And yet I don’t feel at all bad about feeling small. Quite the opposite, in fact. Geology also makes me feel intimately connected with the earth and its great story. There’s an unbroken thread that connects me personally to every other living thing on earth today, and to everything that has ever lived on this planet. We are all related; all the same family. And I’m today’s representative of one fine strand of that beautiful unbroken thread. Rocks enable me to feel this. No man-made thing, no religion, could ever, ever do that.

A few days before my Lake Mary stroll, I’d been hiking on a mountainside among bright red rocks that formed in an ancient desert during the Triassic period. The Triassic actually contains a very boring collection of rocks, but for very interesting reasons. There aren’t many fossils in them, partly because all the continents on earth were joined into one giant supercontinent at the time, whose interior was a blistering hot desert, but more interestingly because the junction between the Permian and Triassic periods marks a truly massive extinction event, during which up to 96% of all marine species and 70% of terrestrial vertebrate species were wiped out, never to be seen again. There aren’t many fossils in the Triassic because life on earth had been almost competely destroyed and it took millions of years for it to crawl back from the brink.

Holding one of the Burgess Shale fossils. That dark smear is from the creature's body fluids!

 

But in these Technicolor red rocks that I was hiking on, I came across some thin white bands. These turned out, on closer examination, to be evaporites from the bed of an ancient, dried up lake. And in the chunks of friable white rock I found some thin, tendril-like grooves and some tiny black dots. With a hand-lens I could see that the dots were the same thing as the tendrils, just seen in cross section as they disappeared into the rock. They were black because they still contained their original carbon. I was looking at tiny plant roots, a quarter of a billion years old.

I sat down on this ancient lake bed and held these frail remains in my hand. The owners of these tiny roots had once clung desperately to life on a hostile desert lake shore and maybe even had to contend with early dinosaurs trampling all over them and crushing their leaves (they had no flowers, since flowering plants hadn’t yet evolved). Perhaps the one I was holding had only lived a year. The local earthquake faults might only have shifted by a fingernail’s thickness before this vegetation succumbed to the summer heat and left its delicate root fibres behind in the salty, preservative mud for all eternity. But nevertheless we had shared this beautiful planet, this little plant and me. We were both lucky enough to have had our moment in the sun. It had its moment two and a half million centuries ago, and here was I, two extinctions later, in the same warm Arizona sunlight, having mine.

I held my delicate fellow earthling in my hand and we communed.

 

Upper Lake Mary from the dam. Lake Mary fault is to the right and Anderson Mesa to the left.

It’s that time of year again…

Grand falls at Grand Falls

Sorry, I couldn’t resist the headline. But it’s okay – I didn’t hurt myself. I just slipped on some lava. Yesterday I took the day off and went to a place called Grand Falls, so I thought I’d share it with you.
Arizona is stuffed full of gems that they hardly ever bother to tell you about. I guess if you have the Grand Canyon in your backyard it’s kind of embarrassing to admit to all the other wonders of the world that you have tucked away in corners. Anyway, this little marvel is actually in the Navaho Nation, some miles down an unsignposted gravel track called Indian Road 70. It’s in the volcano field just north-east of Flagstaff, among huge, arid cinder cones and on the edge of the Painted Desert, precisely where you don’t expect to find a waterfall that’s taller than Niagara Falls. I had absolutely no idea it was there, a few miles from my apartment, until my geology book just happened to fall open at the right page yesterday morning.

The San Francisco Peaks, with a couple of small cinder cones in the foreground

Grand Falls is on the chocolate-colored Little Colorado River – the baby sister of the one that made the Grand Canyon. Around 20,000 years ago, one of the nearby volcanoes erupted and spewed a tongue of lava across the desert, blocking the river canyon completely. The river wasn’t having any of this, so it found another way round, and ended up spilling in from the side of its former canyon. It dries up in the Summer, but at this time of year the snowmelt creates a series of cascades, followed by two stages of falls, totalling 185 feet.

Visitors sun themselves on spray-nourished grass, oblivious to the huge wall of lava advancing from behind

While I was at the lip of the canyon I took a pleasant stroll along the beach. What? In Arizona? Well yes, except that the beach was 225 million years old. The mudstones here were formed on a muddy coastal plain, and their original bedding planes are exposed once more on the desert floor. I was hoping for some dinosaur footprints, but no such luck. Even so, it’s incredibly satisfying to sit on a mud surface that formed so long ago and still see little pockets of shells, animal burrows and dessication cracks from the scorching Triassic sun. What a joy to be able to step back in time and sunbathe on a beach that has barely changed since a quarter of a billion years before humans evolved! Alright, so the sea is now hundreds of miles away and there’s sagebrush and tumbleweed where once there were cycads, but I could practically smell the brine and hear the plopping of muddy reptilian feet.

These hard pebbles were rounded slowly by waves, 225,000,000 years ago, and are now high and dry in the desert.

A little hollow in the mud had filled with sea shells. I wonder what made it?

Dessication cracks, formed while the mud was still soft (notice the lips on the crack sides). It looks like things may have been slithering about over the surface, too

Something lived here that burrowed into the mud between tides

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Anyone know what these nodules were formed by? There were lots of them.

[Update on the nodules above: Norm tells me they may be concretions cemented by hematite that are known around here as ‘moqui marbles’ and possibly similar to purer hematite concretions found on Mars!]

The falls itself is an amazing place. Anywhere else it would be a major tourist attraction, but it’s on Indian land, far from the highway, and the locals seem quite happy to keep it to themselves. There’s not a lot of water in Arizona, so I’m not surprised! In another 20,000 years the river will probably have reclaimed its course and worn away the falls, so catch it while you can, I say.

A sense of the scale - you can see this boulder on the right of the first photo

Cascades of chocolate

Down is optional; up is mandatory

Check out pics of my backpacking trip into the Grand Canyon last weekend.