Hotspot volcanoes

Cornish volcanoes that were active hundreds of millions of years ago

You might find it hard to imagine, but Cornwall’s past includes barren deserts, terrifying prehistoric beasts, and volcanoes.

Our county was once an active region of volcanism, and lava-spitting volcanic eruptions shaped the local landscape for millions of years to come.

Although Britain’s last volcanoes are believed to have erupted around 60 million years ago, if you look closely enough you can still see evidence of Cornwall’s volcanic past.

One of Cornwall’s major volcanoes was located where Cawsand now stands on the Rame Peninsula.

The area between Kingsand and Sandway is considered to be the only site in Britain where you can see a rhyolite rock exposed lava flow, which is a type of volcanic rock.

Earlier this month, layers of an ocher, rust, brown and white substance, which turned out to be ancient volcanic ash, appeared on the recently exposed rock at Sandways Beach.

“This was the origin of the ash that erupted from the Cawsand volcano around 280 million years ago and over the years gradually turned into clay,” said Vanessa Killops, a local passionate about geology.

Bentonite clay forms from weathering volcanic ash in seawater. At the start of the process, it is usually white or pale blue or green, but then turns cream before turning yellow, red or brown.

Ms Killops, who has studied geology and researched the secrets of Cornwall’s physical nature, said Cawsand Volcano was an acid volcano – steep-sided with thick lava.

“Cornwall, at the time, was near the equator,” she said. “When the volcano was active, the area had a rugged landscape, much like Chile.

Ancient volcanic ash in Cornwall

“There was sticky lava, or viscous lava. Lava gets sticky when there’s a lot of water. It’s slow, no faster than 10 km an hour.

“But because they’re so sticky, they’re very explosive. An eruption would cause hot ash and large, glowing clouds.

“It must have been a pretty big volcano at one point.”

According to the Rame Peninsula Beach Care website, you can still find gas bubbles in the exposed rock between Kingsand and Sandway Point, which is now a Sites of Special Scientific Interest (SSSI).

There is more evidence of ancient volcanic activity along the Cornish coast.

Pillow lava, named for its distinctive pillow shape, can be found along the South West Coastal Path at various locations including near Port Isaac, St Ives, Pentire Point and Portloe.

Pillow of basalt lava at Gurnard’s Head in Cornwall

It is believed to have been formed by volcanic eruptions around 400 million years ago, when Cornwall was deep underwater.

Writing on basalt lava found at Clodgy Point, near St Ives, geological society said, “When basalt lava erupts into the sea, rounded pillow shapes form.

“These 400 million year old cushions must also have been formed by underwater volcanic eruptions, showing that during the Devonian period this part of southwest England must have been under water. D ‘Other evidence shows that Cornwall was in deep water, while parts of South Devon formed shallow coral reefs with a coast further north. “

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A volcanic map of the United Kingdom, produced by Daily inheritance, shows that there is also a volcanic plug just eight nautical miles from Land’s End. It currently houses the Wolf Rock Lighthouse.

He said: “Wolf Rock, a single rock located 18 nautical miles east of St Mary’s, Isles of Scilly. The rock consists of a small plug of phonolitic lava formed at the beginning of the Cretaceous period.

“A volcanic plug, also called a volcanic pass or lava pass, is a volcanic object created when magma hardens in a vent on an active volcano.”

But Cornwall has changed dramatically over the past hundreds of millions of years. The volcanoes have been eroded, so there is no need to worry about a volcanic eruption anytime soon.