Arenal is what is known as a stratovolcano: a tall, symmetrical volcano that is built on successive layers of rock, ash and lava. Due to the convergence of tectonic, oceanic, and continental plates, magma (the molten or partially molten rock that forms beneath the Earth’s surface) rises into Arenal’s volcanic chamber and may eventually erupt from its deepest point. high.

Plate tectonics is the theory that the Earth’s outer shell is made up of plates, which have continued to move throughout Earth’s history. The theory explains the dynamics of mountain formation, earthquakes and volcanoes. It also explains how similar animals came to live on what are now widely separated continents.

You probably wouldn’t recognize Earth if you could see it 225 million years ago. At that time, all the major continents formed a giant supercontinent, called Pangea. About 200 million years ago, Pangea began to crack and split. The buildup of heat beneath Pangea may have initiated this split. The ocean-filled areas between the new subcontinents and continental masses continued to move apart, on separate plates, until they reached the positions they occupy today. In fact, the continents are still moving.

It is not known precisely what drives plate tectonics. One theory is that convection within Earth’s mantle pushes the plates in the same way that air, heated by our bodies, rises and is deflected by the ceiling. Another theory proposes that gravity pulls on the colder, heavier ocean floor more strongly than the newer, lighter seafloor, allowing the upper layers to separate.

Regardless of what drives the movement, plate tectonic activity takes place at four types of boundaries: divergent boundaries, where new crust forms; convergent boundaries, where the crust is consumed; collision boundaries, where two land masses collide; and transformation boundaries, where two plates slide against each other.

The size of the Earth has not changed significantly in the last 600 million years. In fact, it probably hasn’t changed much since its formation about 4.6 billion years ago. As Harry Hess surmised, the Earth’s unchanging size means that its crust must be destroyed at roughly the same rate as it is created. Along convergent boundaries, where the crust is destroyed (recycled), plates move toward each other. Sometimes one plate sinks (or subducts) beneath the other. This plate sinking occurs along a place called the subduction zone.

If we knew how to pull a plug and drain the Pacific Ocean, we would see an astonishing sight: an ocean floor cut by narrow, curved trenches stretching thousands of kilometers long and 8 to 10 km deep. These trenches are the deepest parts of the ocean and are created by the process of subduction.

At a depth of between 190 and 430 miles (300 and 700 km), the rock of a descending plate begins to melt. Most of this molten seafloor becomes part of the Earth’s mantle, perhaps to reappear at a distant divergent boundary. However, some reaches the Earth’s surface and produces volcanoes.

The type of convergence that occurs depends on the type of lithosphere in question. Convergence can occur between an oceanic plate and a continental plate (as in the case of Costa Rica’s Arenal Volcano), or it can occur between two oceanic plates or between two continental plates.

Continental plates, which are composed of less dense material, generally overlap oceanic plates. The magna, which is generated from the melting subduction plate, is lifted and compressed in the cracks. Finally, it reaches the surface in the form of a volcanic eruption.

Approximately 85% of stratovolcanoes are found around the Pacific Ocean, forming the so-called Ring of Fire. They are found at the convergent margins of tectonic plates, where large sections of the Earth’s crust move together and where a plate subducts.

Magma

Magma is molten or partially molten rock that forms beneath the Earth’s surface. It is a hot molten mass of silicate, carbonate or sulfide containing dissolved volatiles and suspended crystals. It is generated by a partial melting of the Earth’s crust or mantle and forms the raw material for all the igneous processes that feed the volcano. When magma erupts to the surface, it is called lava.

Magma rises from its region of origin, in the mantle or lower crust, and enters a magma chamber. This part of the volcano’s «piping system» acts as a temporary storage reservoir and is typically located beneath the summit of the volcano at depths of less than 5 km. From the magma chamber, it can supply fresh material for eruptions by ascending a central «chimney», known as a volcanic product or tube.

Arenal Volcano’s magma contains high levels of water and other chemicals, making it highly explosive, like the Stromboli Volcano in Italy.