Headwater erosion rates are estimated at 1.4–2.1 cm/year (0.55–0.83 in/year). The tops of these sequences are characterized by 8–10 m (26–33 ft) of highly resistant vesicular basalt and the contact between these layers controls the shape of the falls. The columnar basalt rock sequences are part of the 1,000-metre-thick (3,300 ft) Serra Geral Formation within the Paleozoic- Mesozoic Paraná Basin. The steps are 35 and 40 metres (115 and 131 ft) in height. The staircase character of the falls consists of a two-step waterfall formed by three layers of basalt. The first European to record the existence of the falls was the Spanish Conquistador Álvar Núñez Cabeza de Vaca in 1541. In a rage, the deity sliced the river, creating the waterfalls and condemning the lovers to an eternal fall. Legend has it that a deity planned to marry a beautiful woman named Naipí, who fled with her mortal lover Tarobá in a canoe. The name Iguazú comes from the Guarani or Tupi words " y", meaning "water", and " ûasú ", meaning "big". Below its confluence with the San Antonio River, the Iguazu River forms the border between Argentina and Brazil. For most of its course, the river flows through Brazil however, most of the falls are on the Argentine side. The Iguazu River rises near the heart of the city of Curitiba. The falls divide the river into the upper and lower Iguazu. Together, they make up the largest waterfall system in the world. Iguazú Falls or Iguaçu Falls ( Guarani: Chororõ Yguasu, Spanish: Cataratas del Iguazú Portuguese: Cataratas do Iguaçu ) are waterfalls of the Iguazu River on the border of the Argentine province of Misiones and the Brazilian state of Paraná.