Every island is dramatic, some with huge volcanic lakes and others with vast dry calderas, places where deep caves and bubbling mud make life unique. It’s easy to see that volcanic activity created the beautiful Azores islands, but how does it all work and what’s been going on for the past several millions of years? Here’s an article for the geology geeks amongst us. We hope you enjoy this plain language deep-dive into some of the earth’s most extraordinary hidden processes.
The Azores – Volcanic activity wherever you look
The Azores sit on top of the Azores Plateau, an area where the earth’s crust is unusually thin, formed long ago by the violent volcanic activity that happens where three of the planet’s huge tectonic plates meet: in this case the North American, Eurasian, and African plates. This unique meeting point is why the islands and their surroundings experience such a lot of ongoing seismic action.
Each of the nine islands in the archipelago is a hotspot of volcanic activity, which is still going on, alive and well, as the enormous plates rub together, clash, crash, slide and dive under or over each other. This has been taking place for millions of years. Add erosion by the weather and you get the stunning array of Azores landscapes visitors love, from the fertile green pastures and dense forests to the rugged coastlines, towering cliffs and craggy peaks.
So what, exactly, are tectonic plates?
Here’s our brief description of tectonic plates, handy because you’ll know what you’re looking at once you get to your chosen island or islands.
Tectonic plates are rigid chunks of the earth’s outer shell, a bit like the crispy shell of a Smartie. There are around a dozen big ones and a load of smaller plates, which interact with each other in different ways to affect the size, shape and look of the earth’s continents and oceans. They’re what causes most of our planet’s geological activity, and some say without the plates there wouldn’t be any life on earth at all.
The power of these enormous movements causes earthquakes, volcanoes and mountain ranges to form, and humans are affected profoundly by them. Take the Himalayas, made when one plate crashed into another and buckled the rocks, forcing them high above sea level. Without tectonic plates the Himalayas wouldn’t exist and the high barrier they create between Indian and China simply wouldn’t be there. Would we still have Chinese people and Indian people without the Himalayas as a barrier? Or would everyone look the same because there was never a physical barrier separating them? It’s an interesting thought!
So the crust is the outer layer, divided up into tectonic plates. Under that there’s the mantle, a fluid layer on which the great plates float around, driven by powerful molten rock movements called convection currents. Underneath all that, the outer and inner core complete the picture. As a rule, Oceanic Plates tend to be thinner and denser than the plates that form our continents, called Continental Plates. Composite Plates are a blend of the two, continental and oceanic.
Drama happens wherever the plates meet
The places where the plates meet are where the action happens, and there are three sorts of Plate Boundary. Divergent Boundaries are where the plates move away from each other, letting molten rock rise up and flow into the gap. This is what created the famous Mid-Atlantic Ridge, visible on Google Earth and marking the area where the Eurasian and North American Plates are moving apart.
When the plates move towards each other they’re called Convergent Boundaries. When one plate is forced under the other you get a ‘subduction zone’ that makes mountains or creates volcanoes. That’s how the Himalayas were formed, when untold amounts of rock were forced upwards by the colliding Indian and Eurasian Plates. These zones also create undersea trenches like the vast Mariana Trench, a mysterious place we know less about than we know about deep space.
When the plates slide past each other you get a Transform Boundary, which creates the kind of friction you need to make earthquakes. The San Andreas Fault in California is one of them, leaving people at constant risk of a quake so powerful it could smash America’s west coast to pieces.
Luckily these plates only move a few centimetres a year, but it adds up over millions of years into something extraordinary. Although our planet is quieter and calmer than it was millions of years ago, areas called hot spots, where plumes of hot magma still bubble up from deep within the mantle, remain responsible for ongoing volcanic activity. The Hawaiian Islands are a good example, marking the place where the Pacific Plate moves over a stationary hotspot. Their word for lava is Pāhoehoe, but there are many specific words and phrases used by local people to describe different aspects of lava and the way it behaves.
The volcanic origins of the Azores
Now to the Azores themselves. The islands were formed by volcanic activity over millions of years, first kicking off about 10 million years ago and leaving the islands volcanically active to this day. The Azores sit at the intersection of the Mid-Atlantic Ridge, where the North American and Eurasian plates are moving apart, close to the Azores Plateau. The African Plate also plays a part, with some subduction zones and ‘faults’, which you get when huge chunks of rock shift in relation to others thanks to the violence beneath. The 2004 tsunami was created by a fault deep under the ocean that moved rocks on one side of so violently it displaced an ocean’s worth of water.
The islands are home to active and dormant volcanoes. Pico Island features the highest peak in the Azores, Mount Pico, an enormous stratovolcano that’s still very much alive and kicking. Fogo Volcano on São Miguel Island last erupted in 1563, while Sete Cidades and Furnas – also on São Miguel – offer bubbling geothermal activity along with steaming hot mineral-rich springs. Looking at them in all their strange glory makes it easy to imagine the distant past when volcanic activity was a lot more violent and common, and dinosaurs roamed the earth.
The Azores’ calderas, in other words volcano craters, are world famous, some with charming local legends and stories attached. They’re made by volcanic cones that collapsed after erupting. Some have filled up with water to become lovely scenic lakes, for example Lagoa das Sete Cidades and Lagoa do Fogo, both on São Miguel. You can hike the rim of some of them, complete with extraordinary views, and there are countless brilliant official viewpoints to take photos from.
Then there’s the Geothermal Activity, harnessed by the islanders for heat and to generate electricity. Hot springs, steam vents called fumeroles and pools of boiling mud are a feature of the Furnas Valley on São Miguel as well as other islands. Earthquakes are also frequent but usually pretty low-key these days, an everyday thing that doesn’t often freak the locals out.
All this means the islands are famed for their beautiful volcanic soil, created from eroded volcanic rock and enriched by aeons of rotting vegetation. That’s why agriculture is such a big deal in the Azores, and the milk from local cows is so delicious. Crops like tea, pineapples and grapes are a big deal, along with masses of lush vegetation that supports a wide variety of wildlife. The wine is uniquely good, grown in dark volcanic soil and sheltered from the winds by walls made from chunks of fine black basalt rock.
Visit the Azores to know the earth under your feet a lot better!
These volcanic islands offer visitors a wonderland of rugged coastlines, high cliffs, volcanic cones, crater lakes and verdant forests, a place where natural beauty, not beaches and partying, are the biggest attraction. So are you inspired to visit these geologically fascinating island with their unique landscapes and many clear signs of volcanic violence?
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