The 22 square kilometer Soderfjarden crater has undergone many changes, from sinking under ice to becoming agricultural land rich in biodiversity.
More than 500 million years ago, a meteorite crashed into Earth near the Antarctic Circle, leaving a giant crater. Over millions of years, the movement of tectonic plates has brought this “scar” on the Earth’s crust to the Northern Hemisphere.
Today, this ancient impact site is named the Soderfjarden crater. The 22 square kilometer hole is located on the west coast of Finland, near the Gulf of Bothnia, the northern arm of the Baltic Sea. Soderfjarden, more than 5.5 km wide from east to west, is now a cluster of fertile agricultural fields. The hole is famous in the scientific community for its unique hexagonal shape, providing important insights into Earth’s geological history and the dynamic processes that help shape celestial bodies in the solar system.
In Scandinavia, Soderfjarden is not always on dry land. About 20,000 years ago, during the Last Glacial Maximum, a thick, heavy sheet of ice covered the place and pressed the land hundreds of meters down. No longer bearing that weight, the land mass is gradually rising at high speed.
In recent centuries, Soderfjarden began to emerge from the water. It initially appeared as a bay (Soderfjarden meaning “southern bay”), where people fished for pike and perch until the 18th century. As the land continued to rise, the hole became drier and drier, becoming wetlands, and finally inland lowlands.
Initially, sedges and reeds thrived in Soderfjarden. People harvest them as animal feed. In the early 19th century, pumps were installed to drain the crater and increase the area under cultivation. Afterwards, more barns for hay and animal feed sprang up in the pit, peaking at 3,000 barns in the 1940s and 1950s, according to the Soderfjarden visitor center.
Today, most of the pits are used to grow grains such as barley, wheat and oats. The fields are also valuable to many bird species, attracting thousands of white-necked cranes during their spring and fall migrations. Because it is still lowland, the hole still needs to be pumped and drained today.
Soderfjarden attracts the interest of planetary scientists because of its distinctive geometric shape. Some consider this crater “the best example of a hexagonal impact structure on Earth”.
Polygonal impact craters have straight segments along the crater rim, making up only a small portion of all impact structures, which are typically circular. Polygonal craters are also present on the surfaces of several planets, asteroids and moons in the solar system – from Mercury to Pluto’s moon Charon. Equipment on NASA’s Voyager 2, Cassini, MESSENGER spacecraft and several other spacecraft have photographed such craters on celestial bodies in the solar system.
Scientists believe that polygonal impact craters are formed by the underlying geology and that their linear segments form where there are structures such as faults or other cracks. Therefore, this type of crater can provide evidence about the geological past of planets and moons that are difficult to observe from the outside.