Ring of Fire

When most people hear “Ring of Fire,” they think of the geologically active zone around the Pacific Rim. (Or maybe they think of an old song by Johnny Cash, but that is not our topic here.) By geologically active zones, we mean dynamic areas that include volcanoes, earthquakes, or both. Other geologic processes are in play in these zones, but it is mostly volcanoes, earthquakes, and their collateral effects (e.g. tsunamis) that people notice. The Ring of Fire is not found only around the Pacific Rim; it actually exists along the boundaries of large plates of the earth’s crust, known as tectonic plates, as shown in the article linked below:

The tectonic plates shown on the map above exist as large areas of (mostly) solid rock that ride atop the hot, plastic rock of the Earth’s mantle. Think of them as pie crust atop the hot filling of a freshly baked pie. Spoiler alert: you might guess that the Earth’s geology is more complicated than this, and you are correct. We will draw out this thread of thought a little further in a moment, but for now let us note that you can expect volcanoes, earthquakes, or both along many of the red lines (boundaries between adjacent plates) in the map. This includes the red line running along the middle of the Mediterranean Sea. It should come as no surprise then that this area is home to Mount Aetna, Mount Vesuvius, the caldera at Santorini, and many earthquakes. You can also see the red line along the West Coast of the US, home to the famous San Andreas Fault, many other active faults, and the volcanic Cascade mountain range.

Pulling the thread a little further, there are many smaller plates around the edges of the seven large plates noted above. For that level of detail you need to sign up for a geology class at your local junior college, or at least take up some further subject-matter reading.. Meanwhile, we will go on to note that none of these plates are static. They all move, or try to move, apparently driven by long-term convection currents in the hot, plastic rock beneath them. As they move, the boundaries behave in one of several ways: subduction, lateral movement, or separation/spreading.

Sometimes as one plate pushes against another, one of the plates is forced to bend down and dip beneath the other in what we call a subduction zone. The Pacific Plate is subducting (yes, that is a verb) beneath the North American Plate along the coast of Oregon and Washington, and this creates the Cascade volcanoes. A similar process is at work along the arc of the Aleutian Islands, and along the western coast of South America. Sometimes the plates slip past each other, creating extensive fault zones like the San Andreas Fault. And sometimes the plates separate from each other, allowing basaltic rock to come up from the mantle (more volcanoes) to create separation or spreading zones like we see in the mid-Atlantic Ridge that runs sort of north-south through Iceland.

Pulling the thread just a little more, let us note that the theories of plate tectonics explain a lot about geologic processes we see all over the Earth. However, they do not easily explain everything. For example, why are the Hawaiian volcanoes and the Yellowstone caldera located in the middle of major plates rather than near one of the edges? Why did some of the largest earthquakes ever experienced in North America happen at the New Madrid Fault Zone in southeast Missouri and not at a known plate boundary?

Finally, let’s remember that science is a dynamic process of discovery and understanding. People who push back against questions in science neither follow the science nor lead it; they oppose science, sometimes perhaps without realizing it. For example, plate tectonics was seen as suspect foolishness as recently as 50-60 years ago. Then the pendulum swung and anyone who questioned the validity of plate tectonics was considered foolish. Then the pendulm swung in a different direction as people explored exceptions like those mentioned in the previous paragraph. Sound familiar? That’s because this flux in thought reflects human nature, and we see similar behaviors in play in our times when it comes to climate science or public health. Food for thought, and please do not hesitate to exercise your critical thinking by asking good questions. Even if good questions are discouraged. That is how science moves forward.

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