Plate Tectonics:
The plates involved in Krakatau are the Eurasian plate and the Indonesian-Australian plate. At this convergent plate boundary, the Indonesian-Australian plate is sub-ducting underneath the Eurasian plate. Magma is rising up all along that boundary, making Indonesia a very active area.
At a convergent boundary, one plate sub-ducts under another. This allows hot magma from deep inside the earth to rise up into the cracks. Therefore at many convergent plate boundaries, there are continental volcanic arcs, or volcanic island arcs. Some examples of these include: the Aleutian Islands, the Tonga Islands, and the Himalayan's.
At a convergent boundary, one plate sub-ducts under another. This allows hot magma from deep inside the earth to rise up into the cracks. Therefore at many convergent plate boundaries, there are continental volcanic arcs, or volcanic island arcs. Some examples of these include: the Aleutian Islands, the Tonga Islands, and the Himalayan's.