Definitions of eruptive:

• adjective:   igneous rock produced by eruption and solidified on or near the earth's surface; rhyolite or andesite or basalt
• adjective:   erupting or tending to erupt

  Example: "A geyser is an intermittently eruptive hot spring"

• adjective:   of igneous rock that has solidified beneath the earth's surface; granite or diorite or gabbro