Popigai
Key facts
- Country
- Russia
- Diameter
- 90 km
- Age
- about 35.7 million years
- Location
- 71.65° N, 111.18° E
A broad, eroded basin in remote Arctic Siberia, crossed by the Popigai River, with exposures of impact breccias and melt rocks along river banks.
Popigai, in the far north of Siberia, is one of the largest well-preserved impact craters on Earth. About 35.7 million years ago, in the late Eocene epoch, an asteroid several kilometres across struck here, forming a crater roughly 90 to 100 km wide. Popigai is famous for one remarkable thing: it is full of diamonds.
Diamonds from a blast. Most diamonds form slowly, deep in the Earth's mantle. Popigai's diamonds formed in an instant. The rocks struck by the impactor included gneiss containing graphite, a soft form of carbon. The shock wave subjected the graphite to such enormous pressure that some of it turned into diamond and a related mineral called lonsdaleite, all within a fraction of a second. These impact diamonds are small, usually less than a couple of millimetres, and often greyish or yellowish. They keep the flaky shape of the graphite crystals they came from.
The quantity is staggering. Soviet geologists knew about the diamonds from the 1970s, but the information was kept secret for decades. When Russian scientists described the deposit publicly in 2012, they estimated that the crater holds a vast number of carats, more than all other known diamond reserves combined. The diamonds are not gem quality, but their toughness could make them useful as industrial abrasives. So far, the remoteness of the site has kept large-scale mining from going ahead.
Discovery. Popigai was first noticed in 1946, and for years it was thought to be volcanic. In the early 1970s the geologist Victor Masaitis and colleagues recognised shocked minerals and impact melt rocks, establishing it as an impact crater. Today it is one of the best-studied large craters in the world.
A busy time for impacts. The late Eocene seems to have been a busy period for impacts. Popigai formed at almost the same time as the Chesapeake Bay crater in the United States, and layers of tiny glass spherules from around this time are found in ocean sediments worldwide. Some scientists once suggested that a shower of comets struck the Earth in this period. Others think the timing is coincidence. Neither impact seems to have caused a mass extinction, though the Earth's climate was beginning a long cooling around this time.
Seeing it today. Popigai lies in tundra and taiga far from any road, and few people other than scientists ever visit. The crater is eroded, but its basin, its central area and its blanket of breccia (rock made of broken, cemented fragments) and impact melt are still clear in satellite images and on geological maps.
Did you know?
Popigai's impact diamonds formed from graphite in a fraction of a second.
The crater is one of the largest on Earth with much of its original structure still intact.
It formed at almost the same time as the Chesapeake Bay crater on the other side of the world.