Haean, South Korea: is it of volcanic or meteor impact origin?

Question

This is a layman's question. While looking for something I read in the news today, I stumbled upon the Haean region in South Korea (38°17'15.96"N, 128° 7'57.18"E) in Google Earth.

To me it looks either like a caldera or like a meteor impact site. Does anyone know from available facts whether one or the other is true? Wikipedia doesn't say anything about it. Is there any way to tell from the geometric features alone, or does it require taking soil samples from the site?

Interestingly there are some more crater-like features in South Korea (e.g. 37°49'5.12"N, 127° 3'12.53"E, almost perfect circular shape). Can this be considered a result of the proximity of the pacific ring of fire, or is it just too far away?

Answer 1

A Korean here. Haean Myeon in Gangwon-do has two theories of creation. One is Meteor impact and another is differential erosion. There were no meteor related evidence found at Haean so the erosion theory is more agreed upon at the moment.

Direct translation from introduction website for Hae An:

According to the analysis of the granite of the punchbowl basin [nickname for Haean], it consists of 71% feldspar, 22% quartz and 5.7% mica. Feldspar is much more weathering than quartz and mica, and since it is rapidly clayed at room temperature, the lowland is eroded earlier than the current highland with high resistance to weathering, resulting in this unusual branching form.