For centuries, the inhabitants thought they were living on a huge volcanic crater. Until they discovered that they had actually built their city with more than 72,000 tons of diamonds and on the impact crater of a million-year-old meteorite.
The Nördlinger Ries is an almost circular, flat basin with a diameter of 24 km, which lies around 100 to 150 meters below the surrounding plateaus of the Swabian-Franconian Alb. This geographical feature and the richness of the soil – the area is still predominantly used for agriculture today – probably meant that it was already heavily populated in prehistoric and Roman times.
The name of the Ries comes, as you have probably already guessed, from its largest town: Nördlingen. It too was already populated in Roman times, as the excavation site of a former Roman estate proves. However, it was not until 898 that the town’s existence was officially recognized: It was called “Nordilinga” and had the status of a Carolingian royal court.
In the Middle Ages, Nördlingen developed into a rich and important trading center – almost on a par with Frankfurt am Main. This and its status as an imperial city helped the town to grow rapidly in terms of area and population. Most of the sights that still exist today, such as the wall ring and St. George’s Church, were built during this time.
However, as the people of Nördlingen worked on expanding their town, they noticed that the stones they were using for their buildings were shiny. It is not clear whether they did not attach any importance to this, whether they attributed it to superstitious or religious reasons or whether they simply could not explain it. It is also not clear whether they noticed or cared about the geographical features of the Ries in which they lived.
The hidden truth
But even in the 18th and 19th centuries, when new studies such as geology emerged, scientists could not well explain the origin of this 24 km wide crater and its shiny stones – called suevite. Some put it all down to the eruption of a thousand-year-old volcano, others to the consequences of a previous glaciation, some even to the same seismic event that formed the Alps.
It was only when the American geologists Eugene Shoemaker and Edward Chao visited the town in the 1960s that the truth was revealed. They discovered that Nördlingen was not located in a volcanic crater, but in the crater left behind by a meteorite. Fifteen million years ago, an object 1.5 km wide hit the earth at a speed of around 20 km/s (72,000 km/h) and with the energy of 1.8 million Hiroshima bombs detonated simultaneously. A crater with a diameter of 8 km and a depth of 4 km was blown out. However, it was so unstable that kilometer-sized slabs of rock slid down the sides and reshaped it until it became the 24 km wide and 150 m deep cauldron we know today.
The formation of the diamond stone
But how was suevite formed? This was only discovered after Shoemaker and Chao’s visit. Local geologists estimated that the city walls and buildings contained around 72,000 tons of diamonds! On impact, the meteorite smashed through several layers of soil and minerals and hit graphite and quartz deposits. They were heated so much that the carbon bubbles in them almost instantly turned into tiny diamonds. In fact, the temperatures were so high that the thick layer of suevite in the crater took an estimated 2000 years to cool from 600 °C to 100 °C.
Worthless diamonds
Why have these 72,000 tons of diamonds not been mined? Firstly, because many buildings would have had to be demolished. And Nördlingen is far too beautiful for that. Secondly, the size of these gemstones is so extremely small that they have no value, even though it is one of the largest deposits in the world. Similar geological events have taken place around the world, but nowhere is the concentration of gemstones as high as in Nördlingen.
As one of the best-preserved large impact craters on Earth, however, the Ries has proven to be very valuable. In the run-up to their moon missions, the astronauts of Apollo 14 and Apollo 16 underwent training here, where they learned what kind of rock they should bring back to Earth. Today, the Nördlinger-Ries with its idyllic landscapes also attracts tourists and cyclists interested in history and geology.