Rift de Asunción y lago Ypacaraí

The Asunción Rift is a composite tectonic trough in eastern Paraguay, between 25 and 40 km wide, in places filled with up to 2,500 m of sediments. It has three segments: the western one (northwest–southeast, over 90 km, between Benjamín Aceval and Paraguarí), the central one (east–west, 70 km, from Paraguarí to Villarrica) and the eastern one (northwest–southeast, 40 km, from Villarrica to the Ybytyruzú range).

Along those faults, alkaline magmas rose in several episodes (about 126 million years ago in the Cretaceous, others about 60 million years ago in the Paleocene), giving rise to hills such as Acahay and Ñemby and the dikes at Kõi. Lake Ypacaraí, about 90 km² and only 3 m deep on average, sits in a topographic valley created by the erosional retreat of the fault on the rift’s eastern edge.