La Cisnera

Barranco del Azucar

The Barranco del Azucar is a small valley near the town of La Cisnera, containing a deposit of the Arico ignimbrite, which fills an ancient valley floor. Black obsidian blocks have been rounded and flattened forming fiamme structures. This deposit is quite unlike the pumice fall and ignimbrite deposits at Chimiche quarry, as it is lithic-rich and pumice-poor, with similarities to a block and ash flow. Thickness increases towards the base of the ancient valley and clast sizes also apparently increase towards the base of the valley as well, although some measurements in the field may help to determine the exact field relationships and internal structure.

In order to test which type of pyroclastic deposit this is, it would be helpful to complete the following measurements.

Ex 05 - Point count to determine proportions of pumice, lithics and ash

Ex 10 - Measurement of change in clast size vertically and with distance from valley

Ex 11 - Measurement of change in thickness with distance from valley

La Cisnera

The Arico ignimbrite is also exposed in thicker section at Cisnera, where the clast size is smaller and there are structures in the walls of the road cutting which appear to show evidence of reworking by water. We did not visit La Cisnera in 2012, due to the more prolonged stay at Chimiche Quarry.

Tajao Quarry

The return trip to the motorway passes Tajao Quarry, which is the site of the coursework.