Cerro do Jarau
Key facts
- Country
- Brazil
- Diameter
- 13.5 km
- Age
- less than about 134 million years
- Location
- 30.20° S, 56.53° W
A ring of hills rising from the grassland pampas of south-western Rio Grande do Sul, Brazil, near the border with Uruguay.
Cerro do Jarau is an impact structure about 13.5 km across in the pampas of Rio Grande do Sul, the southernmost state of Brazil, close to the border with Uruguay. The hills of Jarau rise clearly above the flat grasslands.
What it hit. Like Vargeão Dome and Vista Alegre, Cerro do Jarau formed in the lava flows of the Serra Geral basalts, which are about 134 million years old, and the desert sandstones beneath them. The rebound of the crater floor lifted sandstone into a central uplift, which now forms the hills, while basalt surrounds them.
Proof of impact. The round structure was long debated; some geologists thought it might be a dome pushed up by molten rock from below. In 2019 a study of sandstone and breccia from the centre reported quartz grains with planar deformation features, microscopic sets of planes produced only by shock, some with two or three sets in a single grain. This confirmed an impact origin.
Age. The impact must be younger than the basalts it struck, about 134 million years old. Its exact age is unknown.
Why it matters. Cerro do Jarau is one of three impact structures in the basalts of southern Brazil, making this region one of the best places on Earth to study impacts into volcanic rock. The impactor is unknown.
Visiting. The area is ranch land. Ask permission before entering private property.
Did you know?
Shocked quartz reported in 2019 finally settled a long debate about its origin.
It is one of three impact structures in the basalt lavas of southern Brazil.
It was once thought to be a dome raised by molten rock from below.