Where is the volcano?
When I first visited Madeira I looked around trying to understand where were the volcanoes that originated the island. But at that time I was not able to find them anywhere.
Previously, before visiting Madeira, I had been at some more recent volcanic islands where I was able to easily distinguish forms of volcanoes in the landscape. In Ilha do Pico, Azores, there is a typical conic shape that still has volcanic activity at the top. The same happens in Tenerife, Canary Islands. In Faial, Azores, if you go to the center of the island you will find a large crater that originated the island. In São Miguel, Azores, you will find several volcanoes scattered along the island. The same happens in Lanzarote, Canary Islands.
But in Madeira it seems that something is missing. Where are the volcanic forms that originated such large amount of basalt rock? If you go to the center of the island you cannot find any preserved crater… Why these forms are not evident in the landscape?
Well, one reason is that the volcanic activity in Madeira is not so recent as the examples given above. Most of the volcanic activity in Madeira is thought to date back to 5-1 million years ago. And since then most of the volcanic forms have been eroded away.
But there is a huge volcanic form which can still be observed some miles offshore. Madeira island is actually a large shield volcano (see types of volcanoes forms in the image below).
The form of a volcano depends mainly on the viscosity of the lava. Lava with high viscosity gives rise to volcanoes that present steeper slopes. Lava with low viscosity generates lower profile volcano edifices, that can spread along vast areas.
Madeira is a large shield volcano
Madeira is located in the middle of an oceanic plate.
There are theories that explain the origin of Madeira island as a result of an hotspot but there are also alternative views that say the island was formed along tectonic faults propagated along the oceanic plate (magma leaked to the surface through these faults). Either way, either through an hotspot or through faults, the chemical nature of magma below oceanic plates usually generate low viscosity lava flows at the surface. This type of lava formed the shield volcano of Madeira.
The typical shield form of Madeira Island can be observed from offshore. When arriving Madeira by plane it is not easy to perceive the volcano form. If you have the opportunity to sail away you will certainly see the large volcano of Madeira. If not, you can always use Google Earth to watch how the island looks like from far away. Here are three different views of the volcano of Madeira Island:
The volcano has been eroded, water streams have dissected it, but its shield shape is still clearly visible.
Volcanism in Madeira is considered to have been fissural (in fissural eruptions lava flows through cracks as opposed to central eruption in which lava flows through a central crater) but as we can see by its shield shape lava eruptions occurred mainly at the center of the island.
Madeira island is only the tip of “iceberg” of the volcano. Actually most of the volcano body is underwater. The edifice of the shield volcano stands on the bottom of the ocean at a depth of 4000 m. Above water the island reaches a maximum altitude of “only” 1862 m.
In the following image you can see a comparison between the volcano of Madeira and another shield volcano. Mauna Loa, in Hawai, is considered to be the largest shield volcano of the world. The image also depicts Mount Rainier which is not a shield volcano, it’s a massive stratovolcano well known in the United States, located not in the ocean, but in the state of Washington.
As you can see the volcano of Madeira is smaller than Mauna Loa but is still a large shield volcano and is an edifice much larger than the great Mount Rainier. So large but so easily overlooked by most people who visits Madeira. Well… I hope that now you know where the volcano of Madeira is.
Other volcanoes in Madeira Island
In the later stages of volcanic activity scoria cones were formed along the island. These are smaller volcanoes. Some of them have its shape quite well preserved.