Maar or Meteorite Crater?

A maar is a peculiar sort of volcano, more of a sneeze than a pot-boiler as volcanoes go. It results when molten rock forcing its way up from the depths lacks the pressure to emerge at the surface, but approaches closely enough to come into contact with the groundwater table. This creates all sort of havoc, characterized by an explosive blowout of steam, smoke and ash, but no lava flow.

Several maars are located on the Alaska Peninsula. On April 6, 1977, two of them erupted near the south shore of Lake Becharof, blasting huge clouds into the sky. Impressive as the display was, no human casualties resulted, and the students at Naknek High School named the new features Ukinrek, which means "two-holes-in-the-ground" in Yupik Eskimo. The name stuck, and is used by scientists today.

Just 75 miles to the northeast, in Katmai National Monument, lies another crater which was formed when there was nobody around to record its birth. This feature is called Savonoski crater. It is an anomaly in an area already famous for its numerous craters, because scientists are uncertain about the exact nature of its origin.

A volcanic origin would be expected from crater-like features in such a volcanically active area, but Savonoski crater occurs in sandstone, instead of basalt or other type of igneous rock, and it looks very much like a meteorite crater. It is about a third of a mile across with a pronounced rim rising above the surrounding terrain, characteristic of meteoritic impact. Water fills the crater to the level of its outlet to the Savonoski River, but this in itself is not diagnostic of craters formed in any particular matter.

The difficulty in identifying and classifying Savonoski crater lies in the fact that it was formed before the last glacial epoch, and any meteoritic debris which might have been left has long since been carried away by the ice. A second line of evidence that could prove that Savonoski crater is of meteoritic origin would be the discovery of shock features in the fabric of the surrounding rock. Such evidence, if it exists, has not yet been found, possibly because these layers, also, have been scoured away.

Possibly the only way to resolve the riddle of whether Savonoski crater is a maar or an impact crater would be to drain the lake and examine the rocks at the bottom. But it is probably just as well and just as interesting to let it remain as one of Alaska's many natural puzzles.