THE 1730-1736 ERUPTION OF LANZAROTE, CANARY-ISLANDS - A LONG, HIGH-MAGNITUDE BASALTIC FISSURE ERUPTION

The eruption that took place in Lanzarote between 1 September 1730 and 16 April 1736 differs from the normal style of the historic (last 500 years) volcanism of the Canary Islands. The duration (2,056 days), extent (200 km2), volume of materials emitted (3-5 km3) and the evolution of magmas from extremely SiO2-undersaturated lavas (melanephelinites) towards olivine tholeiite compositions are quite unique in the historic trend of volcanism in the Archipelago, and, apparently, even in the Earth's historical record of basaltic fissure eruptions. However, no specific work has been undertaken until now to attempt the reconstruction of this eruption. We present here a detailed reconstruction of the eruption, based on field observations and data provided by eye-witness accounts, one of which is a hitherto unpublished manuscript. The ''anomalous'' nature of this eruption in relation to the historic volcanism of the Canaries-especially the continuation of the eruption after the initial phase was completed (some 3-4 months, the maximum duration of any historic eruption in the Canarian Archipelago)-might be the result of upward movement of the magma generation front to an intermediate depth along a large fracture.