The geology of the Mount Fuji is a rather complicated and enigmatic natural phenomenon that scientists continuously research. The subject is of much interest not only for its general explanations of volcano origins, but also for the fact that the volcano is dangerous for human civilizations and the more we know about it, the easier to predict its eruption.
The Mount Fuji is probably a contestant of Vesuvius in its fame and geology intricacies. It sits atop the Ring of Fire - a geological seam of colliding tectonic plates that arc around the Pacific Ocean. Actually, Fuji stands right in the place, where the Eurasian Plate, the Okhotsk Plate and the Philippine Plate meet. They form the western part of Japan, the eastern part of Japan and the Izu Peninsula respectively.
Fuji has erupted no less than sixteen times since 781 AD. Most of these eruptions varied from moderate to moderate-large and caused much damage, but no fatalities.
Initially, researchers thought that the volcano had been created by three major eruptions. However, a three-year drilling project, which ended in February, 2004, revealed the evidence of an older eruption. Therefore, scientists conclude that the Mount Fuji geology was formed in four distinct phases of the volcanic activity. The first phase, called Sen-komitake, is composed of an andesite core, recently discovered deep within the mountain. The second phase formed a basalt layer, called Komitake Fuji, several hundred thousand years ago. Approximately one hundred thousand years ago, "Old Fuji" was formed over the top of Komitake Fuji. The modern, "New Fuji", is believed to have formed over the top of Old Fuji by around ten thousand years ago. As a result, all these layers of lava, ash and other volcanic elements have formed the highest mountain in Japan.
The crater of the Mount Fuji has two thousand feet (six hundred meters) in diameter and it consists of three volcanoes -the Komitake Volcano, the Ko-Fuji and Shin Fuji, the youngest one. It is a large composite stratocone, consisting of alternating lava flows and pyroclastics. The last eruption took place from December 1707 until January 1708 with the ashes thrown as far as Tokyo (seventy miles away). Some geologists see the Fuji Mountain as a dormant volcano, while the others consider it active with a low risk of eruption. According to the studies of the mountain's geology, it can only erupt in the case of a strong earthquake; thus, special equipment is set near the mountain to measure the volcano's activity. Nevertheless, it should not be necessarily an earthquake, which will wake up a dormant volcano, but any significant change of the earth surface can result in an eruption as well. To detect those changes, there are satellites with special tools that take precise measurements of the earth's surface. The information about any changes allows the locals to prepare for a coming disaster.
Although today no thermal anomaly is detected, the scientists consider that the volcano can soon blow again. The instability of the lowest crust of the area, where the Mount Fuji is located, attributes to the possibility of an unexpected eruption.