There's a bit of a misunderstanding here. Neptune doesn't have ice volcanoes in the traditional sense. What we see on Neptune are cryovolcanoes.

Here's the breakdown:

* Cryovolcanoes erupt ices instead of molten rock like traditional volcanoes. These ices can be water, ammonia, or methane.

* Neptune does have cryovolcanoes, but their size is not well-defined.

* The most famous cryovolcano on Neptune is Triton, a moon of Neptune.

* Triton's cryovolcanoes are massive, with some reaching heights of several kilometers.

So, while we don't have specific sizes for the cryovolcanoes on Neptune itself, we know that they are large-scale geological features similar to those found on its moon Triton.