Serra do Vulcão

What secrets does Serra do Vulcão hold? Serra do Vulcão isn’t a volcano, despite its name. It’s a peak near Cabuçu, about 3.7 km west of the area initially mistaken for a volcano. This often causes confusion. The actual area studied for volcanic activity is a horseshoe-shaped valley 2 km south of Nova Iguaçu’s urban area. Serra do Vulcão offers stunning views. It sits within the northeastern flank of the Mendanha massif. Peaks over 400 meters high, like Contenda Rock, Austral Rock, Confeito Rock, and Contento Peak, encircle the valley. These peaks reveal pyroclastic rocks. Pyroclastic rocks are essentially aggregations of rock fragments formed by volcanic explosions. This geological makeup sparked the initial, incorrect theory of an extinct volcano in Nova Iguaçu. Geologists Klein and Vieira proposed this theory in the 1980s based on the pyroclastic rocks and a perceived crater-like valley formation. The theory gained traction, even inspiring a “Volcano Exposition” and influencing tourism. However, scientific studies published in journals between 2006 and 2008 debunked the volcano theory. The valley walls are not steep enough to be a crater. The rocks within the valley are primarily trachyte, not the expected volcanic breccia. The supposed “volcanic bombs” turned out to be weathered trachyte fragments. The trachyte itself is older than the surrounding syenite, indicating it’s an intrusive rock formation, not a lava flow. While there’s no volcano, Serra do Vulcão and the surrounding area offer a glimpse into ancient volcanic activity. The region experienced eruptions around 60 million years ago. The geological formations now visible are actually remnants of the volcano’s underground structures, like the magma chamber and conduits, exposed due to uplift and erosion. These exposed subterranean structures are a rare geological phenomenon. So, Serra do Vulcão is not a volcano. However, it presents a unique geological story and a fascinating tale of scientific discovery.