Iso-Naakkima
Finland·Mesoproterozoic·Proterozoic·eroded
Iso-Naakkima is a lake in Southern Savonia, Finland, notable for concealing an eroded impact crater beneath its northwestern section. It is recognized as one of the oldest known impact structures on Earth, estimated at 1200 million years old, and is also among the smallest confirmed craters of its age, measuring approximately 3 km in diameter.
Key Facts
- ›The Iso-Naakkima impact structure is located under the northwestern part of Iso-Naakkima lake in Finland.
- ›It is estimated to be approximately 1200 million years old, dating back to the Mesoproterozoic era.
- ›The crater has a diameter of about 3 km, making it one of the smallest known impact structures older than a billion years.
- ›The remnant of the crater is approximately 2 km wide and 160 meters deep.
- ›Its existence was revealed by circular geophysical anomalies and later confirmed by drilling.
- ›The discovery of the Iso-Naakkima impact structure was made in 1989.
About Iso-Naakkima
Iso-Naakkima Impact Structure
The Iso-Naakkima impact structure is a significant geological feature located in Southern Savonia, Finland, concealed beneath the northwestern portion of Iso-Naakkima lake. It is notable for being one of the oldest confirmed impact craters on Earth, with an estimated age of approximately 1200 million years, placing it within the Mesoproterozoic era. Despite its ancient origin, Iso-Naakkima is also one of the smallest known impact structures that are older than a billion years, measuring about 3 km in diameter.
Discovery and Characteristics
The existence of the Iso-Naakkima crater was not initially apparent from surface observation. Its presence was first indicated by distinctively circular geophysical anomalies concentrated within a 3 km diameter region. Subsequent drilling confirmed these findings, revealing the buried structure. The remnant of the crater is reported to be approximately 2 km wide and 160 meters deep. The impact event occurred when the continent of Baltica, which now forms northeastern Europe, was situated near the equator. The crater is presently filled with recent sediments and is not visible on the surface. The discovery in 1989 marked Iso-Naakkima as the fourth recognized impact structure in Finland.
Source: Wikipedia ↗
Frequently Asked Questions
Where is the Iso-Naakkima impact crater located?
The Iso-Naakkima impact crater is located in Southern Savonia, Finland, situated beneath the northwestern part of Iso-Naakkima lake. It is approximately 10 km south of the town of Pieksämäki.
How old is the Iso-Naakkima impact crater?
Iso-Naakkima is considered one of the oldest known impact structures, with an estimated age of about 1200 million years. This places the impact event in the Mesoproterozoic geological era.
What is the size of the Iso-Naakkima impact crater?
The impact crater has a diameter of approximately 3 km. The actual remnant of the crater is measured to be about 2 km wide and 160 meters deep.
How was the Iso-Naakkima impact crater discovered?
The existence of the Iso-Naakkima impact crater was initially suggested by striking circular geophysical anomalies. Its presence was later confirmed through drilling results. The discovery was officially made in 1989.
Is the Iso-Naakkima impact crater visible on the surface?
No, the Iso-Naakkima impact crater is not visible on the surface. It is covered by recent (Quaternary) sediments and is largely concealed beneath Iso-Naakkima lake.
Related Impact Craters
Keurusselkä
The Keurusselkä impact structure is a remnant of an ancient crater discovered in 2003 on the western shore of Lake Keurusselkä in Central Finland. Identified through shatter cones and shock metamorphic features in quartz, it is one of the oldest known impact structures in Europe, dating back approximately 1.14 to 1.15 billion years. Despite significant erosion, evidence suggests potential ring structures and a negative gravity anomaly, making it a subject of ongoing geological investigation.
Paasselkä
Paasselkä is an eroded impact crater located in Southern Savonia, Finland, forming an oval-shaped lake. The impact event occurred approximately 1800 million years ago, affecting ancient crystalline rocks and sandstones. Its unusual shape and associated magnetic anomalies led to its suspicion as an impact origin, later confirmed by deep drilling, making it the ninth known impact crater in Finland.
Söderfjärden
Söderfjärden is a polder in western Finland, recognized as an impact crater that formed over 640 million years ago. Despite its significant size and the buried central uplift, the crater is primarily visible today as a large, hexagonal cultivated field due to its filling with Cambrian sandstones. This unique surface visibility distinguishes it from other Finnish impact structures.