The Great Pleistocene Ice Sheets

I sat in on a scientific talk at the Cascades Volcano Observatory today, and was reminded of some old and learned a number of new, interesting things (interesting if you live in the Pacific Northwest, that is):

1. There are two kinds of glaciers:

(a) Alpine glaciers are the ones derived from snow falling on a high mountain, accumulating as ice, not melting much because higher elevations are always colder, and thus forming slow "ice rivers" down the flanks of the mountains. These are so common in Alaska, Canada, and the Pacific Northwest that many of them even have names - especially when they are on volcanoes. In fact, there was a dog-fight going on in 2004 about what to name the crescent-shaped glacier forming behind the 1980-86 dome of Mount St Helens. One party wanted to call it "Crater Glacier", while another wanted to call it "Loowit Glacier" (if you follow that link, you will come to an amazing Native American myth).

The glacier's name all became moot when the volcano erupted again in October 2004 and split the 200-meter-thick (600' deep) glacier into an "east arm" and a "west arm". I was one of the last four people to walk between the two arms' northern meeting-point in August 2007, when I was helping a geophysics team make some geoelectrical soundings there. The 10-month winter closed in shortly afterwards, and by 2008 the two 25-meter-thick (75' deep) glacier "toes" had merged. One of my geoelectrical sounding stations, that "saw" down at least 950 meters (~1,000 yards), is now under the merged glacier, and can never be reoccupied again. At least in my lifetime, anyway.

(b) Continental Ice Sheets are the monster ice sheets that form pretty much like Alpine glaciers - but form over land that is constantly being snowed on and not warming up enough to melt away. In North America these have waxed and waned for millions of years, the last set melting back only about 10,000 - 17,000 years ago (depending on where we are talking about) to expose what we now call New York, and Vancouver, and Chicago... and a place called Canada. In northern Europe, these great ice sheets grew to be at least 3 kilometers (~2 miles) thick, and so heavy that they actually depressed the crust of the Earth by hundreds of meters (the Earth's crust is plastic over long stretches of time).

2. Glaciers 'majorly' change the face of the land. Because of climate change, virtually all glaciers remaining have been retreating for close to a century - longer in some cases. They leave behind several very distinctive land-forms:

(a) weirdly U-shaped valleys. They are "weird" to someone who has worked most of his life in a desert, anyway. These valleys are the living proof that something very big scraped and scoured all the loose edges free of...

(b) huge piles of boulders and rocks. These huge piles now form distinctive land-forms called "glacier moraines" - typically long, skinny ridges of rocks and bounders. The Hill Cumorah is a classic example of a glacial moraine. Huge rocks (called "glacier erratics" for fairly obvious reasons) have been identified with a source terrain that can be literally hundreds of miles north of where they now lie. If you ever drive through the northern half of the United States, you will often see huge, house-sized boulders sitting in the middle of a field somewhere. All the smaller ones have been bulldozed aside by the farmers, leaving an odd distribution of only the ones to big to move. These typically came from Canada.

3. There is a Pacific Decadal Oscillation going on: this is a roughly 10-year cycle of cold and wet periods interspersed with warm and dry periods, and they roughly oscillate in 10-year high/low cycles in the Pacific Northwest. It's often hard to sort these out in the short term, because they mix with the ENSO (El Nino-Southern Oscillation) events that most people have heard of. We are currently in a cooler-wetter part of a PDO cycle, which can easily fool certain people who can't accept that climate change is going on - because some glaciers are actually increasing a bit (Mount St Helens' still un-named glacier[s] is an example). If you look at the plots of glacier length over a 60 - 100 year scale however (when we had grandparents with a scientific bent who recorded such things), you will see a long, steady decline with 1 - 3 year increase 'spikes' on it.

4. Continental Ice Sheets can also make major, long-term changes in rivers. The Alaska Panhandle (the southern "tail" of Alaska) is an "accreted terrain" - that means that island arcs of volcanoes forming in the Pacific ocean migrated over time (or the North American continent encroached on it, from another frame of view) until they smashed up against the continental margins. Then another one came and smashed up against the first. And then another. Geologists have dated some of these by radiometric means back to the Jurassic era, up to 200 million years ago. Same thing happened to the Pacific Northwest: what my house is built on wasn't originally even part of the North American continent, but some island paradise (or volcanic hell-hole).

Now think of your kitchen baking experience. If you keep kneading bread in one direction, then bake it, you will see inside it that it has a certain texture - a preferred way to split apart, for example. This becomes really obvious if you sprinkle cinnamon and sugar on one surface and then roll it up: you've created a naturally weak zone just like a sedimentary layer made of mud that becomes a shale millions of years later. Bingo: a preferred place for a fault to happen if you have tectonic forces at work. Ever see a pile of really, really beat-up, shattered rock? This is often a quick way to identify shale from a distance even before you can lay a hand (or hand-lens) on it.

In the Alaska Panhandle and the Pacific Northwest, the "incoming" oceanic terrains came from the west-southwest... this means that the "texture" trends north-northwest (perpendicular to the "smashing force"). If you are going to have valleys and ridges, they will align this direction: the "softer" rocks weather out preferentially, while the tougher rocks become the ridges. At one time all the rivers in the Pacific Northwest DID align north-northwest. The Frasier River in British Columbia and the Skagit River north of Seattle are examples.

However, when the great continental ice sheet came grinding and crushing down from the north, it blocked these rivers and dammed them up. This caused great, long lakes to form until they got so deep that they started spilling over one of the lower points of the bounding ridges. You know what water breaking through a hoed row in your garden does: it rapidly widens the opening. Thus the Skagit River, which once flowed northwards, made its way steadily westward (a lake at a time) and now opens out to Puget Sound north of Seattle. Early geologists couldn't figure out why a river would cut through a landscape instead of follow that landscape. No one understood this until they understood continental ice sheets.

For a different reason (the blockage was not ice, but HUGE amounts of flood basalt magma) huge lakes formed in what is now the interior of the northwestern United States. Bonneville Salt Flats? After a long time Lake Bonneville drained westward, leaving the salty, flat bottom behind. The Columbia River? It finally broke through a lower point in the dam basalt (pun intended) and ripped open the Columbia River Gorge, and now they all drain to the Pacific Ocean.

And all this just because water freezes.

Incidentally, there are all sorts of other wide-scale interactions involved:


(a) For example, when northern Europe and North America and Asia were covered with huge ice sheets, the oceans had quite a bit less water. What you may now refer to as "Virginia" or "Florida" actually extended at least 50 kilometers farther eastwards. Native Americans' ancestors cooked mussels and clams on beach dunes that are now 7 meters (~20 feet) under the sea.

(b) While all this was going on, today's deepest and driest desert, the 'Rub al-Khali (Empty Quarter) was quite literally THE Land of Ten Thousand Lakes (sorry, Reo). I have a photo of myself standing next to what looks like the skull and horns of one really different-looking water buffalo - an antique bovid that roamed in those lakes. I have personally dug up fresh-water shells from the desolate desert floor there. This is a region where "normal" humidity can get down to 2% - you wake up every hour, all night long, with your nostrils on fire, and you MUST drink and "snuff" water or you will end up with a bloody nose. Everyone sleeps on their sleeping bags in the Empty Quarter, and no one sleeps very well.

(c) Ocean currents were totally different: the Gulf Stream... wasn't. For that matter, if the Gulf Stream somehow was ever blocked, you can wave goodbye to London and the rest of Europe, because don't look behind you but a huge ice-wall is fast approaching. This has actually happened a number of times in the last several millions of years.

~~~~~

Heat Flow

How are the other planets like - and unlike - our Earth?  To answer that very fundamental question, at the dawn of the Space Age my friend and fellow USGS scientist Gene Shoemaker founded the Branch of Astrogeology in Flagstaff, Arizona. He and his many fellow scientists there have figured a LOT out about the other planets by using data and imagery provided by NASA.


Q:

I am told that the core of the earth is as big as the moon and as hot as the surface of the sun, and that the mantle is pretty darn hot too...


Why doesn't all of this heat transfer, move through, conduct up through the crust so that the surface of the earth would at least be very warm to the touch?


peter h

A:

The Earth's core is not quite as large as the Moon - it's about 70% of the Moon's radius using evidence accumulated from the seismic tomography studies over the past half century or so. Think: earthquakes send sound waves downwards, and sophisticated calculations convert the refracted waves and their arrival times into an image of the Mantle and the Outer Core and the Inner Core. No one has ever measured the Core's temperature directly, of course, but laboratory high-pressure experiments, along with theoretical calculations, suggest that the temperature may be in the 5,400C/9,800F range - pretty close to the surface temperature of the Sun.

Actually the Core's heat DOES transfer outwards, and in some pretty spectacular ways: parts of the Earth's crust (Kamchatka, for instance) are moving as much as 8 cm/3 inches per year under the convective force of that heat trying to escape.  Think: this crustal movement is analogous to the skin moving on the surface of a pot of cooking Cream of Wheat. This is the reason we are seeing those monstrous earthquakes off the coast of Chile, Japan, and in Haiti.  The fact that heat escapes from the core is also manifested in the hundreds of volcanoes we see, for instance, all around the Pacific Ring of Fire.  The continental crust rides up and over the down-going (denser) oceanic crust, which melts as it goes deeper and gets hotter, and the lighter water-and-gas-saturated components work their way upward through that continental crust to give us things like Mount St Helens.  

Heat flow is actually a venerable (old and respected) field of geoscience. There are specialists who study heat flow all their professional lives - you have to put sensors deep in wells and block the fluids from convecting in order to get accurate numbers. There are places like Battle Mountain, Nevada, where the heat flow - the amount of heat escaping through a square meter of the surface - is several times higher than it is, on average, elsewhere on the Earth's crust. Another manifestation of that heat flow is the fact that no matter where you are on the Earth's surface, you can go down in a mine a few tens of meters/yards, and the temperature will almost always be about 55 degrees F (12 degrees C). It could be 122F/50C on the surface, and it will still be that cool at depth. It could be 'way below freezing on the surface in the Arctic, and it will STILL be 55F/12C at a drill-able depth. As you go much deeper, perhaps 4,000m/12,000 feet deep in some of the South African gold mines, the temperature gets hotter and hotter the deeper you go. A friend told me that in one South African gold mine, the temperature at the rock face at those depths can be 140F/60C.  The deeper you go, the hotter it gets.  

Why isn't the crust hot to the touch?  For the same reason that a cinder-block wall is good insulation against the heat of the day-time sun. Rock is just not thermally conductive like a metal is - it's usually a pretty good insulator, in fact. For this reason, when the heat can't easily get out by conduction, it gets out by convection, but at a much slower rate.  Think of that pot of Cream of Wheat again - that's convective heat transfer going on. On the global scale of the Earth's crust, this is the same thing as continental drift... which gives us huge subduction earthquakes and volcanoes.  

~~~~~

Sea Level Rise

One of the more startling side effects of Climate Change is sea level rise. (Yes both are very real, and the only partially unanswered question is how much of it you and I as human beings have caused ourselves.) There is a loud scientific cat-fight going on about sea level rise - and another equally loud one as to whether climate change is the reason for the increasingly violent weather extremes we've been seeing. These recent extremes include multi-year droughts in Texas and the Southwest, EF-4 tornadoes in the Midwest in March, monster hurricanes in the East Coast and similar typhoons in the western Pacific, etc.  Oh: One of the more obvious pieces of data is that nine of the hottest ten years on record historically have been in the past decade: in this century. 

For some people there is a growing realization that sea level rise can have some rather direct personal consequences. As in property-loss. As in losing your entire country.

Q:

Sorry for the rather twisted syntax here, but my kids are interested to know whether about 250,000 years ago Virginia's Atlantic coast was generally farther east or west of today's coastline. In other words, was more of what is now Virginia covered by the Atlantic ocean then than today? Thanks for any help or direction you can provide.
Mike M.


A:

Good question - you have smart kids to even think about this - and a firm number here is hard to pin down precisely. The following link will give you an image of seawater high-and-low stands over the past 900,000 years: http://en.wikipedia.org/wiki/File:Sea_level_temp_140ky.gif

The short answer is that 250,000 years ago there was substantially more of Virginia than there is today: the coastline went much farther east than it does now.

I know relatively little of Virginia's coast and offshore topography except for the (probably exposed then) Smith Shoals, where I dragged an electrical geophysical streamer behind a ship not so many years ago looking for titanium-bearing placer sands. All I remember was days of 5-meter (15-foot) seas and a long-term case of seasickness. Only 4 people of a ship's compliment of 19 even bothered to go for lunch or dinner. The data were good, though.

To put things in perspective, just 17,000 years ago the northern Florida coastline was about 50 kilometers farther east than where it is today. In a Gulf Coast estuary I've seen side-scan records that show a beach berm 6 meters below modern sea-level - and when it was tested with a vibracore, there were burned seashells in the sample.

Translation: They saw and drilled a paleo-indian campsite that is now 20 feet below modern sea-level.

What is interesting to me in that chart is not so much the cyclic nature of sea-level stands, but the fact that the most recent sea-level stand is the highest. THAT tells me two things:
1. The Virginia coast today has the least land area in the past million or so years, and...
2. At current generation of CO2 (historically this was around 280 ppm in our atmosphere; it is now closing in on 400 ppm), it means that Virginia is about to lose even more land to the sea as Antarctica and the Greenland ice cap melt - which appears to be accelerating vis-a-vis their state even 50 years ago.

So... don't look for long-term investment on beach-front property.

FOLLOW-UP:


Q:
Was it because the atmosphere was colder and there was more sea ice than now?

A:
Seawater stands were lower then because monstrously huge glaciers covering most of the northern hemisphere were greatly expanded and tied up so much surface water. In Norway the glaciers were 3 kilometers (two miles) thick. And yes, that means colder (as an average) by many degrees C everywhere.

Q:
Were ALL the seas lower?

A:
Yes. There are tectonic movements - for instance, Scandinavia has been and still is rebounding many meters (about 1 cm/year) since the "ice monster" glacial cover melted - and these sea level changes are 'relatively' persistent. Ports have had to be repeatedly relocated in Scandinavia because of this. In most of the rest of the world, however, sea level is creeping up. Also, seawater seeks its level worldwide - like if a flood inundates a city, the water gets everywhere quickly. Tides and large storms (typhoons, hurricanes) will temporarily raise local sea level, but it will always re-equilibrate to provide a "Mean Low Water". This is a legal term used to define edges of seafront property - I was once threatened as part of a USGS survey team in Alaska because of a drunk property owner not understanding this. MLW is what is now starting to change as the glaciers melt ever more rapidly, and huge chunks of the Ross Ice Shelf break off and float away from Antarctica. I suspect sea level rise will soon (if not already) match or overmatch the isostatic rebound in Scandinavia. Low-lying places like Tuvalo and the Seychelles are already actually witnessing the frightening loss of their entire countries! Because of tides and storms, it takes a lot of recording over many years to be certain of the actual sea level rise.

Q:
What about on the west coast?

A:

Same - all sealevels rise at the same time. The latest world-wide data says the water is moving up about 3.1 mm per year (EOS, 6 December 2011). That's an inch every 8 years, 16 inches a century.  Another recent paper (EOS, 8 November 2011) points out that the huge groundwater depletion going on all around the world is increasing river flows... and adding to the sea-level rise. The Washington Post (22 March 2012) reports that a new long-range military assessment is predicting water wars this century - people going to war over water rights!

~~~~~

Fracking

Probably the hottest geologic topic right now is called "fracking", which is short for "hydrofracking", which is short for using water (hydro) pumped down wells at enormously high pressures to fracture (frack) so-called gas-rich "tight" rocks. The idea is that a huge formation found all over the north central and northeastern US, called the Marcellus Shale, is... well, shale. Shale is a rock formed from deeply rich, usually black muds at the bottom of swamps. These muds are loaded with carbon, because they are mostly organic in composition (e.g., "stinking swamp muck"), and carbon usually "matures" under heat and compression to a number of different forms ranging from coal through liquid hydrocarbons to different forms of carbon-based gas. A major component in the Marcellus is methane, a.k.a. natural gas. But shale itself looks typically like a dark gray to black, raggedy-edged yard stepping stone. It's just a gassy version of stepping stone.

This particular shale formation is widespread, extending from New York state (whose town of Marcellus is the type-locality) throughout much of Appalachia. It is OLD: around 400 million years old (Devonian age). It is also "tight", which oil drillers coined to refer to a rock that didn't let gas or fluid pass through it very easily. However, if you can break up the formation - fill it with fractures - then just the pressure of the overlying rock could potentially force trillions of cubic feet (the standard measurement of natural gas) out of your well. And guess what? The Marcellus is located strategically close to where it would be needed most: the northeastern US.

Fracking, however, means more than just water being injected. It also involves proprietary (e.g., secret) mixes  of solvents and lubricants and sand. Yes sand: after the hydraulic pressure is released, the particles of sand will keep those new fractures open so the natural gas trapped in the shale can get out. And the lubricants and solvents are designed to keep the fluids flowing - keep everything slick, not gooey. The theory, of course is that the top kilometer or so of the frack well is cased (lined with steel tubing) and that tubing is cemented into the hole to stop any potential leaks. This in most cases will extend beyond the groundwater being used by overlying communities and keep the fracking fluids and your drinking water separate.

The idea is that the solvents will sort of, you know, be nice, stay where you put them, and behave themselves. Here's a clue for you to think about however: the secret nature of those mixes. Why keep those chemicals secret unless you are trying to hide something? Another thing to think about: no underground system is "closed" - sealed off for eternity from everything else around it. Groundwater specialists know that there is always movement of groundwater through the sands and rock that it saturates. That movement can be as low as a few tens of centimeters per year, but is often far higher than that. So anything underground is not going to stay where it is - unless it's solid. Maybe you can see where this might lead to by now. There are whole communities in Appalachia, Colorado, South Carolina... and for that matter all over the world where the groundwater is poisoned for one reason or another. It could be mine waste leaching into the ground in West Virginia or Colorado. It could be a leaky tank beneath a service station in Illinois. It could be an abandoned landfill from a World War II Army base in Arkansas. It could be a plutonium-loaded and corroding tank on the Hanford nuclear facility near Pasco, Washington... leaking into the adjacent Columbia River that runs through Portland, Oregon. I kayak in that river, so it gets personal.

And "stuff" always moves.

Q:

I'm in the middle of a PhD in economics right now at University of _, and right now I'm working on possible dissertation projects. One project I've been thinking about is looking at gas drilling (specifically fracking), and looking at the economics of drilling. For example, I'm thinking of looking at the economic impact of drilling in the Marcellus Shale formation in Pennsylvania, where there's been a recent expansion of fracking.
I have a geological question for you that I haven't been able to figure out. Is there a way to determine a map that gives both (1) the depth of the top of the Marcellus formation and the (2) depth of the bottom of the Marcellus formation? When I look at standard geological maps, there doesn't seem to be a way to convey that information well in a 2D map, since the information I'm trying to figure out is 3D. I don't know how well this information is known. I imagine that mapping it would be tough, since it is expensive to take deep-earth samples.
Eric L.

A:

You have certainly picked a relevant (and highly politicized) subject - and one that will remain relevant for many, many years. Look forward to full employment for a long time! What you are searching for is an Isopach map - a map contouring the thickness of a particular sedimentary unit - of the Marcellus Shale. You can be absolutely certain that the Oil & Gas companies have these. These are what they base their drillstring-whipping efforts on: where to guide the drill (first downwards, then they "whip" it horizontally to follow a particular stratigraphic horizon). It's a 100% bet that if they DIDN'T have this information, their efforts would be a hugely expensive bust: it's not economic if a million-dollar drill-stem can't be contained within the producing horizon. The stratigraphic unit of interest can be quite thin, but spread over a large area - that's where the dollar value starts clocking in. The strata are almost never horizontal and rarely stay at the same depth over any significant distance, either, so you need to know where the top is and where the bottom is.

This inherently 3D information is generally obtained using 3D reflection seismic surveys... very expensive, but current technology has the capability of resolving layers as little as 5 meters thick when buried more than 2,000 meters down. It's really amazing where brains and (nearly) unlimited resources can bring technology these days.

One reason that this is not found much in modern geologic maps is that the graphic systems used to display and evaluate the unit(s) of interest are also 3D - the top and bottom of the Marcellus is inherently three dimensional so must be viewed that way to be meaningful. The display technology is handled using workstations costing $20,000 or more, with software that is far more costly still. Generally the people working with these data - and planning the drilling programs - are using 3D glasses and working off of multiple 50" plasma screens.

The problem facing YOU (and also the US Geological Survey) is that this information is highly proprietary: one oil company has very strong incentives to keep the information secret from competitors... AND from government entities that might want to tax and/or regulate them. I know some people in the Energy Program of the USGS these days... but their programs are more oriented towards doing large-scale resource estimates. THESE things are available in the public domain: http://energy.usgs.gov/. If you want more detailed information on the Marcellus Shale, my first recommendation is to get in touch with one of the "Minors" - smaller Oil & Gas companies working the Marcellus right now - and see if you can meet with one of their geologists. Explain what you are trying to do, and see if they might be willing to talk with you and share some of their data (perhaps even show their 3D data to you, after you sign a non-disclosure agreement).

~~~~~

A Desert vs a Tundra

Like all science fields, there have been arguments on what a particular word really means. In the example below from the USGS Ask-a-Geologist website, the question comes up: what is a desert? Would the Antarctic qualify? Does a desert have to be hot and sandy?

Q:

Hello!
I'm having an argument with a friend;
What is the largest desert? The Sahara or Antarctica?
Can Antarctica be considered a desert or a tundra?
What is the difference between a desert and a tundra?
Thank You,
Ashlee C.

A:

Hi, Ashlee,
Here's the dictionary.com definition of a Desert :
–noun
1. a region so arid because of little rainfall that it supports only sparse and widely spaced vegetation or no vegetation at all: The Sahara is a vast sandy desert.
2. any area in which few forms of life can exist because of lack of water, permanent frost, or absence of soil.
3. an area of the ocean in which it is believed no marine life exists.
4. (formerly) any unsettled area between the Mississippi and the Rocky Mountains thought to be unsuitable for human habitation.
5. any place lacking in something: The town was a cultural desert.

Here's the definition of a Tundra:
–noun
one of the vast, nearly level, treeless plains of the arctic regions of Europe, Asia, and North America.

Some Additional Information:
The Sahara covers about 8.6 million square kilometers; I have spent time there and it is pretty huge, but not a contiguous sand-dune desert like the smaller Empty Quarter in the Arabian Peninsula. You can at least drive across the Sahara and have a chance of getting to the other side.

Antarctica covers about 20 million square kilometers - quite a bit bigger.

From the definitions above, Antarctica is a Desert, but not a Tundra. The Sahara is a Desert, but not a Tundra. Antarctica is more than twice as big as the Sahara.

I hope this settles your argument.

~~~~~

Volcanoes, Earthquakes, and Plate Tectonics

Yes, they ARE connected.

With two notable exceptions, volcanoes are associated with (a) tectonic plates splitting apart (Iceland and east central Africa come to mind) or (b) tectonic plates that are coming together (the Pacific Ring of Fire comes to mind). In the former case, magma is simply rising into an opening gap between crustal plates that are being pulled apart - like the mid-Atlantic Ridge. In the latter case, an over-ridden oceanic plate, loaded with water and chemical sediments, heats up as it goes deeper into an increasingly-hotter-with-depth mantle. Something called partial melting takes place: the lighter materials like silica and water and CO2 segregate from the down-going slab and float up - Mount St Helens in the Pacific Cascades, Sheveluch in Russian Kamchatka, and Mount Fuji in Japan are examples of these.

The notable exceptions are the volcanoes of the Hawai'ian Islands in the middle of the Pacific oceanic plate, and Reunion Island in the Indian Ocean. The generally accepted understanding for their existence is that a "hot spot" in the Mantle feeds up through a moving crust (the Pacific plate) and creates a string of volcanoes. In the Hawai'ian chain, the oldest are in the northwest, and the youngest are in the southeast on the Big Island. There's even a new one, called Loihi, that is forming on the ocean floor even farther southeast of the Big Island.

When we talk about moving tectonic plates, it's hard to come up with a reference point that everything is moving with respect to... Certainly the North American continent is moving westward over the Pacific and subsidiary plates, but Kamchatka is moving southeast over the same plate(s). If in fact there IS a "hot spot" in the middle of the Pacific plate - perhaps that is the one non-moving reference point on this entire planet.

Q:

With the increased recent activity around the "ring of fire", New Zealand, Japan and Gulf of California, is there an increased risk for earthquake in other areas of the ring of fire?
Thank you
David H


A:
Geologic events never happen according to a regular clock - sometimes things are quiet around the Ring of Fire, sometimes several events happen in relatively close succession. There is no recognized relation between the huge Tohoku earthquake in Japan and the much earlier Christchurch, New Zealand event - they are too far apart in both space and time. THAT said, there have been several cases observed where a large earthquake has "lit up" distant volcanic or earthquake-prone areas.  The large Denali fault earthquake of November 2002 apparently triggered swarms of small earthquake in Yellowstone, for instance. Nothing big happened, but there were a cluster of small earthquakes that correlate closely with the p-wave of the Denali event passing through.

The likelihood of other earthquakes around the Ring of Fire correlates much more closely with the rate of subduction - how fast the continental plate is over-riding and "smothering" the oceanic plate. This rate is much higher off the coast of Kamchatka, in eastern Russia for instance (about 8 cm/year), than the collision rate of the Pacific Northwest (moving only about 2.5 cm/year). For this reason the volcanoes in Kamchatka are historically much more active than those in the Cascades. In the 10 years that I've been receiving daily volcanic notices about Kamchatka, I'm at a loss to think of a time when a volcano in Kamchatka was not erupting. Whereas in the last century, here in the Pacific Northwest, we've only had Mount Lassen erupt (1915-17), then Mount St Helens in (1980-86).

Any plate motion will translate into earthquakes - the plates are scraping past each other - and the subduction (over-riding plate) earthquakes can be real doozies.

Slower tectonics translates to a quieter life: fewer earthquakes, fewer volcanoes.

~~~~~

Nuke it!

While I was serving as the chief scientist for volcano hazards of the US Geological Survey, Mount St Helens chose that time to erupt (October 1, 2004). At the time I was also still volunteering to answer questions for Ask-a-Geologist. Perhaps because of my calling at the time, I received not one but two AAG queries that went something like this (I couldn't find them in the archives or I would quote directly):

Why can't you drop an atom bomb on <Mount St Helens> to stop it from erupting?

A variant on this suggestion is to use a nuclear device to trigger a pending eruption at a time of your choosing.

There are several problems with this approach:
A. Highly radioactive debris scattered widely over a populated area.
B. You would need to get the device under the ground to open the ground.
C. The inherent energy of most volcanoes is far larger than any nuclear devices built by man.

"A" is, I hope, obvious. Nearly as many people died of radiation poisoning after the Hiroshima uranium bomb was dropped than died of the immediate blast itself. Half-lives for things like the unstable isotopes of strontium and cesium are looooong - thousands of years - and they are poisonous the whole time they are decaying. Plutonium is, gram for gram, far more deadly than botulinum toxin.

"B" is basic physics. A small stick of dynamite will blow OPEN a standing safe by over-pressuring it, but a cluster of dynamite sticks taped to the outside and detonated may or may not crush a safe door down onto the inner contents of the safe. Despite what you may have seen on Butch Cassidy and the Sundance Kid, safes don't blow up nicely.

Translation: you will need a very big, very expensive drill to place the nuclear device at a strategic place. Assuming it was powerful enough, that is.

When you come down to the many trade-offs, it's far easier to just (1) monitor the volcano, and (2) evacuate people when it's restive behavior starts accelerating and the seismometers start going ape on you.

"C" is just a numbers game. The Hiroshima uranium bomb and the Nagasaki plutonium bomb had estimated explosive yields between 12,000 and 20,000 tons of TNT. For you metric nerds out there, a metric ton of TNT equivalent is a bit over 4 gigajoules.  Mount St Helens' 1980 eruption was a VEI = 5 level blast. That's short for Volcano Explosivity Index, and a VEI 5 is about 10 times bigger than a VEI = 4; the values are approximate, and approximately logarithmic. The 1980 eruption of Mount St Helens released the equivalent of 20 million tons of TNT. That's between 1,000 and 30,000 times more energy released than the Hiroshima atom bomb.

The eruption of Yellowstone supervolcano about 640,000 years ago has been estimated as a VEI = 8 event, or 1000 times larger than the 1980 Mount St Helens eruption. That's between 1,000,000 and 30,000,000 times the power of a Hiroshima bomb.

Translation: a nuclear device is to a VEI 5 volcanic eruption, as a fly doing push-ups is to you doing push-ups. I may be exaggerating a bit with the fly, but you get the point. Volcanoes are BIG. That's why no one has ever seriously considered engineering around a volcanic eruption. Just get out of the way if you can.

If you want to open a can of spinach, ya gots ta squeeze it, to quote Popeye. No sissy atom bombs.

~~~~~