Jisho.org Forum

You don't need any counters (and I'm not aware of any specific for volcanoes or islands, though according to the Japanese wiki, there are about 500 counters in Japanese, most of which Japanese people no longer know, so perhaps they do exist...). Just use 一つ、二つ、etc.

For islands, you could use the counter とう, which is written with the same kanji as しま (i.e. 島).
So one island would be 一島（いっとう）, two islands would be 二島（にとう）etc.

Since a volcano is 火山, you could theoretically use 山 (with the pronunciation さん) as the counter: 一山 (いっさん), 二山 (にさん), 三山 (さんざん) etc.
I think 一つ、二つ etc. are much more common for mountains and volcanoes, though.

The same thing is done with books (using 本 as the counter) , people (using 人 as the counter) and I'm sure I could think of more examples if asked.

I saw on this "How Japanese are you?" type of quiz show that 座 (ざ) can be used for mountains.

:-)

Yeah, I thought about suggesting とう for 島、but for some reason my computer didn't want to complete にとう to 二島, and according to Google, it seems like 一つ、二つ are pretty commonly used for 島. Is the とう counter is more popular? I think it's pretty common for formal writing, but I don't know about normal conversation.

にしま does change to 二島 though. Same with 一島（いっしま）、三島（さんしま）、but that's where the pattern ends. The rest can be forced, but not as easily or naturally as the first three.

Oh, and my dictionary has a section for counters, didn't find anything for islands at all. But then again it doesn't have the volcano counter 座 either.

Posted By: paulusmaximus

[p]I saw on this "How Japanese are you?" type of quiz show that 座 (ざ) can be used for mountains.[/p]

座 za ichi Shinto shrines, (seated) statues, deities; high mountains or forests

島 とう 漢 文語で島を数える　「伊豆七島」