**7. Conclusions**

Stratigraphic units associated with the Guamsan caldera comprise Guamsan Tuff and rhyolitic intrusions. Guamsan Tuff typically consists of volcanic breccia, ash-flow tuffs, and fallout tuffs, of which the ash-flow tuff is very dominant.

Volcanic breccia can be distinguished into the block and ash-flow breccia at the lower part and the caldera-collapse breccia at the upper part, according to their distribution locations and stratigraphic sequence. In the lower member, the ashflow tuffs exhibit expansive pyroclastic flow phase by the pyroclastic flow-forming eruptions, and the fallout tuffs exhibit ash cloud-falling phase, whereas the ashflow tuffs in the upper member exhibit the non-expansive ash-flow phase by the boiling-over eruptions.

Rhyolite intrusions can be distinguished into intracaldera intrusions and ring dike based on location and pattern: the ring dikes are distinguished into the inner, intermediate, and outer ring dikes. The Guamsan caldera represents a caldera cycle connecting into ash-flow tuff—caldera—ring dikes.

The volcanic processes in the Guamsan caldera area can be summarized as the following sequence along the caldera cycle: (1) The volcanic activity began with the Pelean eruption generating block ash-flow phase by a lava dome, and (2) it then subsequently turned into the fluidized pyroclastic flow phase by the collapse of high eruption column. At that time, fluidization of the pyroclastic flow was reduced with gradual decrease in the height of the eruption column. (3) In the transformation into ash-flow phase, boiling-over eruptions burst instantaneously hotter pyroclastic materials to be densely welded. The boilingover eruptions began on their way by migrating vents into ring fracture zones together with the caldera collapse. At the earlier stage of eruption, the pyroclastic flows were produced from a central vent, whereas voluminous ash flows were generated from multiple vents in the ring fracture zone. The consequently accumulated Guamsan Tuff was at least 850 m thick inside the caldera. (4) After the ash-flow eruptions, the magma was injected into fissures in the caldera moat to form the rhyolitic plug and dikes. (5) Almost simultaneously, the magma was successively injected along the ring fracture zone so as to form the ring rhyolite dikes. (6) Finally, the rhyodacite was successively intruded into the junction part of southwestern ring dikes.

## **Acknowledgements**

The work was supported by funding of the Korea Meteorological Administration Research and Development Program under Grant KMI (**2018-01610**) through the Korea Meteorological Institute. We are grateful for the careful approval for our proposal by the editor and reviewer, Professor Angelo Paone.

**63**

**Author details**

Sang Koo Hwang

Andong, Korea

provided the original work is properly cited.

\*Address all correspondence to: hwangsk@anu.ac.kr

*Eruption Types and Processes in the Guamsan Caldera, Korea*

*DOI: http://dx.doi.org/10.5772/intechopen.84647*

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Department of Earth and Environmental Sciences, Andong National University,

*Eruption Types and Processes in the Guamsan Caldera, Korea DOI: http://dx.doi.org/10.5772/intechopen.84647*

*Forecasting Volcanic Eruptions*

long time (**Figure 6e**).

boiling-over eruptions.

part of southwestern ring dikes.

**Acknowledgements**

connecting into ash-flow tuff—caldera—ring dikes.

**7. Conclusions**

a final intrusion along the ring fracture zone of southwestern caldera in Guamsan magmatic system, but they now display their root zones due to deep erosions during

Stratigraphic units associated with the Guamsan caldera comprise Guamsan Tuff and rhyolitic intrusions. Guamsan Tuff typically consists of volcanic breccia, ash-flow tuffs, and fallout tuffs, of which the ash-flow tuff is very dominant.

Volcanic breccia can be distinguished into the block and ash-flow breccia at the lower part and the caldera-collapse breccia at the upper part, according to their distribution locations and stratigraphic sequence. In the lower member, the ashflow tuffs exhibit expansive pyroclastic flow phase by the pyroclastic flow-forming eruptions, and the fallout tuffs exhibit ash cloud-falling phase, whereas the ashflow tuffs in the upper member exhibit the non-expansive ash-flow phase by the

Rhyolite intrusions can be distinguished into intracaldera intrusions and ring dike based on location and pattern: the ring dikes are distinguished into the inner, intermediate, and outer ring dikes. The Guamsan caldera represents a caldera cycle

The volcanic processes in the Guamsan caldera area can be summarized as the following sequence along the caldera cycle: (1) The volcanic activity began with the Pelean eruption generating block ash-flow phase by a lava dome, and (2) it then subsequently turned into the fluidized pyroclastic flow phase by the collapse of high eruption column. At that time, fluidization of the pyroclastic flow was reduced with gradual decrease in the height of the eruption column. (3) In the transformation into ash-flow phase, boiling-over eruptions burst instantaneously hotter pyroclastic materials to be densely welded. The boilingover eruptions began on their way by migrating vents into ring fracture zones together with the caldera collapse. At the earlier stage of eruption, the pyroclastic flows were produced from a central vent, whereas voluminous ash flows were generated from multiple vents in the ring fracture zone. The consequently accumulated Guamsan Tuff was at least 850 m thick inside the caldera. (4) After the ash-flow eruptions, the magma was injected into fissures in the caldera moat to form the rhyolitic plug and dikes. (5) Almost simultaneously, the magma was successively injected along the ring fracture zone so as to form the ring rhyolite dikes. (6) Finally, the rhyodacite was successively intruded into the junction

The work was supported by funding of the Korea Meteorological Administration Research and Development Program under Grant KMI (**2018-01610**) through the Korea Meteorological Institute. We are grateful for the careful approval for our

proposal by the editor and reviewer, Professor Angelo Paone.

**62**
