Geology of Madeira

[citation needed] The high altitude limestones are associated with the Vindobonian Volcanic Complex, which includes trachyte, diabase and dolerite intrusions, along with pyroclastic flow sediments.

Breccia, agglomerate and conglomerate beneath the basalt suggest rapid deposition due to torrential downpours quickly eroding the slope of the volcano, while the lignite indicates poorly drained, swampy depressions.

Eroded sediments in the Miocene and early part of the Pliocene formed laterite, soil enriched in iron and aluminum due to the leaching away of silicate material by rainfall.

Biodetrital sand, leftover from shell debris, is found along the coast of Madeira, in places where the sea level subsequently retreated.

[4] Groundwater on Madeira is held in fractured volcanic rock aquifers, with widely varying transmissivity and dissolved mineral content.