Mid-Atlantic Ridge: The Rise Of The Azores Archipelago

Many a green isle need must be

In the deep, wide sea …


Millions and millions of years ago, the Eurasian and African tectonic plates distanced from the American plate leaving space for the lava to emerge from beneath the Earth’s crust. This still on-going process is thought to have occurred about 200-180 million years ago, when Pangea split forming the northern and southern landmasses, also known as Laurasia and Gondwana, respectively.

The longest mountain range – the Mid-Atlantic Ridge (MAR) – was thus formed, extending for about 16000 km from the Arctic region to a little bit over the South African tip. As the Atlantic Ocean has been expanding ever since, the Pacific Ocean has been swallowed slowly, due to subduction processes (one plate moves under the other), leaving behind the deepest parts of the world, the so-called trenches.

One of the many MAR’s possible heredities that can be visited nowadays is the Azores archipelago, which stands above the Azores plateau. In fact, the plateau represents one of the MAR’s hotspots characterized by unique geomorphology: an oceanic area of around 150000 km, with a magmatic center located 100-200 km east from the MAR axis (Arnould et al., 2019). Beneath the Azores, there lies a relatively vertical conduit, or mantle plume. In short, it is sort of a column that connects the Earth’s hot core with the Earth’s upper crust and through which magma rises by convection in the mantle, causing volcanic activity.

This plume in particular is suggested to have been formed by the shearing due to plate system motion around the ridge and the plume itself.

Surface topography of the Central Atlantic Ocean and potential temperatures obtained from the PRIMELT method along the MAR. The direction and magnitude (in cm/yr) of plate velocities according to their absolute motions during the last 10 Ma in a moving hotspot reference frame in the vicinity of the Azores are denoted by the black arrows and numbers. (Arnould et al. 2019)

Despite the complexity and unclear causes, the northward motion of the Azores plume appears to be consistent with the formation of the Corner Rise and Great Meteor plateaus some tens of millions of years prior to the current plume position.

The Azores, indeed, are characterized by 26 active volcanoes, of which 8 are found under water. In addition to these mantle plume-dependent formations, seamounts are yet another MAR’s complex, abundantly found within the Azores archipelago. Generally, seamounts are defined as any risen formation of conical shape, which elevates 1000 m or more above the rest of the seafloor – imagine it as a submerged mountain that usually does not rise above the sea level, if you will. It originates when a submarine volcano erupts many times, pushing magma towards the shallower waters.

As incredible as it might seem, the Azores archipelago consists of approximately 100 seamounts found thus far. However, more of them will perhaps be found in the near future thanks to advanced technological approaches and more frequent discoveries. Their abundance could appear rather irrelevant but it is not the case since such complex 3D structures represent a joint of particular currents, topography and sediment composition. Together, these features create a perfect place that can be colonized by many organisms, hence contributing to the increase of biodiversity.

(Morato et al. 2008)

Nevertheless, everything will get clearer in the following few weeks, through which we will get deeper to the core of the Azores archipelago. Combining geophysics, oceanography, biodiversity and conservation, we will get a bigger picture of just a small region on the entire globe.

  • Arnould, M., Ganne, J., Coltice, N. and Feng, X., 2019. Northward drift of the Azores plume in the Earth’s mantle. Nature communications, 10(1), pp.1-8.
  • Morato, T., Machete, M., Kitchingman, A., Tempera, F., Lai, S., Menezes, G., Pitcher, T.J. and Santos, R.S., 2008. Abundance and distribution of seamounts in the Azores. Marine Ecology Progress Series, 357, pp.17-21.
  • Rubin, K.H., Soule, S.A., Chadwick Jr, W.W., Fornari, D.J., Clague, D.A., Embley, R.W., Baker, E.T., Perfit, M.R., Caress, D.W. and Dziak, R.P., 2012. Volcanic eruptions in the deep sea. Oceanography25(1), pp.142-157.

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