What am I thinking about? The uncontrollable nature of the planet on which we live and the geologic processes which have been around for the last 4.55 billion (yes, that's with a B) years. And it all boils down to plate tectonics. During my undergraduate years, the theory of continental drift was dying a slow death as a few young geologic mavericks were heralding the new age of geology. From Tanya Atwater, author of the most cited paper in geology (PlateTectonics), to J.Casey Moore's work with accretionary wedges to Eldridge Moores' work on ophiolites, plate tectonics was born with a blast. Anyone who looked at a world map can't miss the way the 'pieces' seem to fit together - it's all about plate tectonics.
Yeah, lots of big words but hang in there with me - all will be explained. My advanced studies were on the termination of the San Andreas fault in the Point Arena basin of offshore California - even if my field area was below 300' of ocean, plate tectonics still ruled the world.
The planet we inhabit is a dynamic place, from the two-part core to the highly mobile crust, things are always moving. All the bits and parts are driven by heat and the juxtaposition of hot things versus cooler things. Think about pouring milk into your hot morning beverage or watch a pot of boiling pasta, what's happening? Convection—hot stuff is rising from the bottom, displacing cooler stuff at the surface which falls to the bottom to be heated and moved back to the surface. It all looks like it's rolling over. That's what happening in the ground below our feet. That's what drives plate tectonics in the near surface and all the deeper planetary processes in the mantle and core.
Okay, so the Earth is rocking and rolling. Next we need to think about time, not time in Einstein's relativistic world but linear time. In geology there are two kinds of time—day to day time, the time we experience as humans and deep time which our planet lives in. Although most geologic processes work over hundreds of thousands to millions of years, there are geologic events which occur in a heartbeat of time—volcanic eruptions, earthquakes, landslides, tsunamis, avalanches, weather events and meteor impacts. Some are not controlled by geologic processes but others are a direct result of plate tectonics. Those are the ones we'll focus on—earthquakes and volcanic eruptions.
A lot of work has been done on 'what we can see' at the surface. But surface features—the Rocky Mountains, the Himalayas, the ocean basins, the shape of the continents—are a snapshot in time and only really show us the last 200 million or so years of Earth's history. How do we know what happened before this and what did the continents look like then?
There are a few places in the world where much older rocks crop-out at the surface—central Canada, South Africa, the Australian subcontinent, Amazonia—this is where scientists have found evidence for when plate tectonics started to move pieces of the crust around and create earthquakes and melt crust to form magma for volcanoes.
Rocks exposed in the Jack Hills of Far Western Australia give us a clue about when crustal movement and plate tectonics started. Here, some of the oldest rocks in the world (>3.85billion years) are exposed at the surface and within these very old sedimentary units are grains of a mineral called zircon. These tiny blue-crystals can form in two ways—precipitate out of a magma (like salt out of evaporating water) or be recycled through erosion and sedimentation to then be carried into the deep parts of the Earth on subducting plates and melted to recrystallize in new volcanic material. By peering into the interior of these crystals we can measure certain properties which allow us to date when events happened. According to the zircons in the Jack Hills, there is evidence plate tectonics started very soon after proto-Earth coalesced. Its hypothesized crustal movement began 4.0 billion years ago. (When It All Began) Have I lost you yet?
Lets take a small step back and talk about tectonic processes—there are two types of plates on the surface of the Earth: heavy oceanic plates (those that floor our oceans) and light-weight continental plates (those which form the landmasses). Because the plates weigh different amounts and thus have different densities, the heavier-more dense oceanic plate can be pushed under the lighter-less dense continental plates. This process is called subduction. It's what's happening along the western coast of South America—the lighter South American continental plate is moving west over the heavier Pacific oceanic plate which is moving east. And along the Aleutian Islands and the east coast of Japan. And offshore Oregon and Washington states. The heavier ocean plate is pushed down into the underlying mantle where it melts. Molten rocks, which are lighter than the solid rock of the mantle, rises—forming volcanoes. Inland from the point where the subducting oceanic plate is falling into the mantle we see a line of volcanoes. Think about where the volcanoes occur in the Andes, in the Japanese Alps, and our own Cascade Range—on the continental plate, parallel to the coast above the subducting ocean plate. They are indicators of molten rock moving up from the melting subducting rocks to erupt on the surface. So we have plate movement, one over the other, which gives rise to volcanoes. Any of which could erupt in an instant.
Volcanic eruptions have been recorded throughout human history. Some massive eruptions have catastrophic effect on the planet and humankind. On 20 May 1883 and for the following 5 months, Krakatoa in the Dutch East Indies erupted. It destroyed more than 70% of its island archipelago, sending massive amounts of debris (>42cubic kilometers of material) into the upper reaches of the atmosphere. This was one of the most deadly and destructive volcanic events. The sound wave was in excess of 310dB and had enough power to circle the globe three times—it was heard as far away as 3000mi (4800km) in Mauritius. The airborne ejecta darkened the sky worldwide and reduced temperatures by 0.4degC while impacting oceanic currents worldwide. The resultant tsunamis were in excess of 46m and their effects were recorded on tidal buoys as far away as the English Channel. In comparison, the 1980 eruption of Mount St Helens erupted 0.003 cubic kilometers of material. Kind of a spit in the ocean in comparison. Volcanoes exist in some of the most heavily populated areas of the world and continue to present a significant geologic hazard. And though they appear to be an instantaneous event, we have many ways to monitor a volcano and estimate an impending eruption (Climate Impact), but are we prepared for the resulting climatic impact of a massive eruption?
An interesting area to watch for potential volcanic activity is Yellowstone National Park. We don't directly equate volcanoes with Yellowstone. It's more geysers and hot springs and bison and elk. But, the heat which drives all the hydrothermal features is derived from molten rock rising from the mantle beneath the park. The area is still very active and risk of another super eruption like the last one which covered most of the US east to the Mississippi River and west to the Central Pacific with a thick layer of ash is possible. Indications are the center of magma activity is migrating northeast (Yellowstone). If a super volcanic eruption would occur it would cover the US in an average 3" of ash. Denver Colorado would experience 4-11" of ash fall.
There is another much more instantaneous geologic event that is a direct result of plate movement—earthquakes. As the plates move past one another or under one another it's not a smooth process— it's actually really hurky-jerky. When the moving plates get caught and can't move smoothly, strain builds up in the rock to the point the rock fails and all that stored up energy is released in one instance.
On October 30th at 8:15 pm, a magnitude 6.0 earthquake occurred 290km west of Coos Bay Oregon under the Pacific Ocean. This event was the result of rocks rupturing at a depth of 10km. Not a big deal, not felt by many, no damage onshore. Okay. But what does this tells us in the long run? The 'Big One', which everyone talks about, is not going to occur in earthquake-prepared Los Angeles or San Francisco. No, the 'Big One' with a magnitude of >8 and potential for massive tsunami will occur offshore from unprepared Oregon and Washington. Here, the Pacific Plate is subducting beneath the North American plate—where are the active volcanoes? In the Cascade Range. A similar geologic setting to offshore Tohoku Japan, where in 2011 a 9.0 magnitude quake happened. The shaking lasted for four minutes, the tsunami reflected around the Pacific Ocean basin for days. (ReallyBigOne)
Think about this - hold your hands palm down and touch the tips of your middle fingers together. Got it? Your left hand is the ocean plate and your right the North American plate. Slide your left hand under your right. This is the subduction occurring now occurring under Oregon and Washington. As you move your left hand under your right, flex your right knuckles up toward the ceiling. Your raised knuckles are the bulge which is growing along the Cascade coastline. Your hands form a 3D picture of what's happening there now. But your left hand can't go under your right hand forever—at some point it will butt up against your wrist. Then what? Everything stops and the strain keeps building up in the left hand (ocean crust) until it breaks. When subduction can't continue, strain builds up until the plates rebound and create the Big One.
Wow, that's a lot of geologic information about some really scary, but statistically rare events which would have global impact. Our climate, our economics, our very life would be at risk. But, not all is doom and gloom. Geologists are getting better at predicting events within a statistical probability of occurrence. And, if the general populace has some basic geological understanding, we can make informed decisions about our future. There is power in knowledge and though we can't tame our planet we can understand it and learn to live safely.
Some good things come from all this global plate movement. Several newsletters ago I shared the fact that some tech companies are restarting nuclear reactors in the US to create energy for their massive server farms—Microsoft, Google and Amazon. Another company is going a different direction to get clean energy—Meta. Meta is building enhanced-geothermal energy stations. Contracting Fervo Energy, Meta will construct a plant in Beaver County Utah to generate 2000 megawatts of energy from heat captured in the subsurface. All the heat is being generated by a subducting ocean plate beneath North America which is slowly falling into the mantle. (Hot Rocks) Be it nuclear or geothermal, AI is a hungry beast for energy.
