Peridot Mesa facts for kids
The Peridot Mesa vent is a special place in San Carlos, Arizona, USA. It's part of the San Carlos volcanic field and is located on the San Carlos Apache Indian Reservation.
Imagine a large, flat-topped hill – that's a mesa! Peridot Mesa is about 3 km (1.9 mi) across. Its top is covered by a layer of hard, dark rock called basalt. This basalt layer is about 3 to 6 meters (10 to 20 feet) thick. It came from a volcanic cone (a cone-shaped hill made by a volcano) located at the southwest corner of the mesa.
Scientists who study rocks, called petrologists, find the lava flow around this vent very interesting. Why? Because it has a super high number of special rocks called xenoliths inside it! Xenoliths are like "guest rocks" – they are pieces of other rocks that got picked up by the molten rock (magma) as it moved towards the surface.
How Peridot Mesa Was Formed
Scientists are still studying and discussing exactly how Peridot Mesa was formed. But they do have some widely accepted ideas about its beginning.
The first eruption was incredibly powerful and explosive. It was a "pyroclastic flow," which means a fast-moving cloud of hot gas, ash, and rock fragments. The fact that some xenoliths found here are as big as a basketball shows how strong this eruption was! The molten rock, or magma, must have been moving super fast to carry such heavy rocks with it.
Scientists at Arizona State University are even studying these xenoliths. They look at the "reaction rims" around tiny olivine crystals inside the xenoliths. This helps them figure out when these guest rocks were picked up and how long they've been part of the lava.
The Lava Fountain Theory
The most popular idea about Peridot Mesa's formation is that a huge lava fountain created this unique flow.
- A lava fountain is when molten rock blasts high into the air, like a giant geyser of lava.
- The lava flow at Peridot Mesa is "rootless." This means it starts outside the ring of volcanic ash (called a tuff ring) that usually forms right around a volcano's opening. This suggests the lava was blasted far away from its starting point by a powerful fountain.
The vent (the opening where the volcano erupted) is called a diatreme. A diatreme is a volcanic vent that was blasted through solid rock by exploding gases. The magma that caused this eruption probably had a lot of water and carbon dioxide in it. These are "volatile substances," meaning they can turn into gas very easily and cause extremely powerful and violent eruptions. The more of these gases in magma, the more explosive the eruption!
The lava flow then moved downhill, following a dip in the land towards the northeast. It carried many small, rounded pieces of peridotite xenoliths that had also been blasted out by the strong fountaining.
Today, the "neck" of the volcanic vent has collapsed. Scientists think that the final stage of the volcano's activity was when the fountaining stopped. The remaining magma then hardened, creating a plug that sealed the vent.
