**5. Postcollapse intrusions**

Postcollapse intrusions in the Guamsan caldera are composed of rhyolitic dikes (60.65 Ma in [9]) and plugs, which are exposed as several lithofacies which are presumably connected to the identical magma chamber beneath the caldera. Based on differences in igneous structures and chemical composition, the lithofacies can be roughly subdivided into flow-banded rhyolite, porphyritic rhyolite, porphyritic rhyodacite, and stony rhyolite. In the field, a single rock body shows change in lithofacies within a few 100 m or a few km. In such cases, the erosion level in the Guamsan caldera area may nearly be approaching the original roof of the intrusions. Thus, according to positions related to the caldera-forming eruption, the intrusions can be categorized into intracaldera intrusions and ring dikes (**Figure 1**). The intrusions into the higher level of the Guamsan Tuff can demonstrate that they are the roots of postcollapse volcano, because the Guamsan Tuff has been of the final products and placed at a higher level as the caldera was formed [12].
