The Geology of the
Lizard Peninsula Words & Photographs by Arabelle Zhuang
The Lizard, Cornwall is the most southerly point of England with breathtaking scenery and rare geology that creates a haven for rare plants, flowers and invertebrates. However, about 390 million years ago, The Lizard ceased to exist. Due to continental drift, dense oceanic rocks of the tectonic plate partially subducted under the lighter continental crust of the plate. It resulted in a convection of magma and major earth movements where peridotite rocks were pushed up from the boundary of the earth’s crust and mantle ploomed. The thrust resulted in the “welding” of the ocean floor rocks onto the continental landmass, which was England. This eventually formed what is now known as The Lizard.
100
NATIONAL GEOGRAPHIC MAY 2017
Kynance Cove, Cornwall. 8 February 2017.
Eroded Granite Batholith at Kynance Cove, Cornwall. 8 February 2017.
T
he geomorphology of Kynance is strikingly beautiful and at low tide, the waves crash onto both sides of a spit off that joins the main headland to a series of seastacks. This landscape is a result of the geology; various rocks of the Lizard eroding at different rates.
The coastal cliff exposures at Kynance Cove provide one of the best and famous exposures of The Lizard serpentinite, and an array of igneous and metamorphic rocks that form it. The rocks found at Kynance Cove was paramount in providing evidence; suggesting that the rocks originally formed part of the ocean floor. The most prominent rock being the Red Serpentine. Because of it’s magnesium and iron minerals, Serpentine is fiery red. It records the part of the Earth’s mantle just beneath the crust. Massive rocks with running veins are also seen scattered throughout Kynance. These are caused by precipitate that flows into areas of low pressure, usually nearer the surface
102
NATIONAL GEOGRAPHIC
MAY 2017
Red Serpentine rocks found at Kynance Cove, Cornwall. 8 Febraury 2017.
Microscopy of Red Serpentine Particles, Falmouth University. 8 Febraury 2017.
of the earth’s crust. When the magma cools, within fractures and cracks, the minerals cool and melt at varying times depending on their crystallisation temperature. The process is called differentiation, where igneous magma separate into two or more fractions in which it consolidates into different rock type. As the precipitate begins to solidify within the fatigued rock, it then forms mineral veins. These minerals can contain gold, quartz or iron. Within the ground water stores of Kynance Cove, there is a network of water channels which eventually becomes visible at the mouth of the drainage basin. Freshwater on land are held within rocks where streams flow through. This supplies water for rare cornish heathland, such as gorse, bramble, heather and fern, to thrive. With flourishing heathland and wetlands, animals find The Lizard a safe haven to call home.
The mouth of a drainage basin moments before being deposited into the sea, Kynance Cove, Cornwall. 8 February 2017.
THE GEOLOGY OF THE LIZARD PENINSULA
103