Prato Sesia GEOSITE
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Title
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Prato Sesia GEOSITE
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Description
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Walking on the outcrop, one can distinguish rocky blocks of different colours, enveloped in a pinkish-yellow tufa; here and there we find reddish
rocks, glassy rhyolites, grey andesites or tuffs rich in rock fragments (Figs. 2 and 3). It is a kind of sampler of the rocks that had formed on the surface during volcanic activity, before the final act: the catastrophic eruption of the Sesia supervolcano some 282 million years ago.
It is estimated that more than 500 km3 of ash and lapilli were erupted in a very short time; at the same time, the entire volcanic apparatus collapsed and huge blocks collapsed into the caldera that had formed, a chasm at least 13 km in diameter. Much of the erupted material fell back into the caldera, mixing with the blocks and forming the chaotic set of rocks we have under our feet: the mega-breccia (Fig 4). Among the fragments forming it, it is even possible to find pieces of the ancient continental crust, also shattered by the explosion, such as the so-called Lake Shale, rocks recognisable by their silvery glow and characteristic foliation (Fig 5).
After the gigantic eruption, the activity of the magmatic system stopped, but many other geological events followed.
We could talk about when the sea arrived or how the mountains were formed: other beautiful stories that our Planet whispers to us. Stories that geologists are ready to listen to, to reveal to those who have never heard them.
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Lithology
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breccia
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Event process
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eruption
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Older named age
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Permian
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Numeric age
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282 My
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Interest
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Petrographic