By exploring Paris' underground tunnels, can scientists identify the original source of Notre Dame's vaulting stone, damaged in the 2019 fire?
Repairing Notre Dame's Vaults with Underground Quarries
Published: January 27, 2021
Narrator: The intense heat from the fire and the collapsing spire took out 15 percent of the stone vaulting. Today, three 40-foot-wide holes and several smaller gaps mean the vaults could collapse at any moment. The team collects, stores and catalogues the fallen stone in this tent. They may be able to use some of this stone to reconstruct the vaults, but it’s clear they’ll also need to source new stone.
Geologist, Lise Leroux investigates what quarry this stone came from.
Lise Leroux: We have some blocks coming from the collapse of the vault for study.
Narrator: The fallen vaulting stone contains a rare micro-fossil called orbitolites complanatus, a kind of plankton. Fossils, like this, are found in just one layer of rock. Can they use this geological fingerprint to discover the original source of the vaulting stone?
Leroux: (Translated from French) Impressive.
Narrator: To find out, Lise and fellow Notre Dame scientist, Claudine Loisel venture deep beneath Paris. Hidden under the city streets is a rich source of limestone, a vast labyrinth of quarry tunnels. Lise and Claudine enter this maze two miles south of Notre Dame, in the famous catacombs.
Claudine Loisel: Ahh!
Narrator: Amongst the bones, Lise and Claudine find traces left by the medieval miners.
Leroux: The block is removed, and so we have the trace.
Narrator: So, back in the lab, she takes a closer look at a sample of limestone.
Leroux: Oh, this one here is orbitolites complanatus! This little planktonic fossil, is a “dating fossil,” which match with the stone coming from the vault.
Narrator: Lise confirms the origin of the Notre Dame vaulting stone. Sourcing more of the correct stone won’t be easy. The old quarries are no longer active. But engineers now know what limestone to look for. This will help them find a match in quarries outside Paris.
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