Like Toshima, the main geological feature of Oshima is one very large volcano, with one very big difference: size. Whereas Toshima is tiny, Oshima literally means "Big Island." Almost a hundred square kilometers and with a population of more than 9,000, it is the largest of the Izu Islands.
The Izu islands were created by relatively recent seismic activity, and Mt. Mihama-Yama in Oshima is a reminder. The last eruption was in 1990, when the entire population was evacuated and lava fountains reached as high as 1600m. To the right is a current satellite photo taken from Google Earth. Once you reach the plateau peak of the volcano, it appears to be nothing more than a black desert. The smaller crater you can see is a product of the most recent eruption.
The main feature of the trip to Oshima was climbing this mountain -- well, at least climbing through the interesting part. Buses are available to the initial plateau, and from there it's a good one hour hike to the crater.
Here you can see a shrine, reconstructed after the eruption of 15 years ago.
This picture was taken after walking for more than 50 minutes, and you can see the path taken on the left. Folliage is slowly retaking the landscape, but most of what you see while walking is black rock.
And the crater, an enormous hole at the top of the mountain, is still smoking from some vents. (Click here for a panorama shot of the crater.)
Finally, a night shot -- the night sky as seen from Motomatchi Port on Oshima.
The trip back to Tokyo took about four hours (although for double the price you can take the "Jet Cruiser" and arrive in under two hours). It was a very fun five day trip. Once again, those interested in taking a similar journey should start by checking out the Tokai Kisen webpage (only in Japanese). Happy trails.