How do scientists monitor volcanic activity at Mount Fuji? What is the likelihood of its future eruption?

Hello! The topic of Mount Fuji is indeed a subject of great public interest. After all, it's not only a symbol of Japan but also an active volcano. Let me break down how scientists are "keeping an eye" on it and assess the likelihood of it "losing its temper" in the future.

The "Check-up Package" Scientists Use for Mount Fuji

Imagine scientists as Mount Fuji's personal medical team, conducting round-the-clock "check-ups" to assess its "health." These examinations primarily include:

Seismic Monitoring: Listening with an "Earth Stethoscope" Before an eruption, magma beneath the surface begins moving, triggering many tiny earthquakes imperceptible to humans. Scientists have installed high-precision seismometers all around Mount Fuji, like countless stethoscopes placed on its body. If these "low-frequency earthquakes" or "volcanic tremors" become frequent or regular, it's like a yellow warning light indicating the giant below might be stirring.
Ground Deformation Monitoring: Checking if the Mountain is "Bulking Up" Rising magma pushes the crust upwards like inflating a balloon. While invisible to the naked eye, precise instruments can detect millimeter-level changes. Scientists primarily use two methods:
1. GPS Systems: Numerous GPS benchmarks are set up on and around the mountain to monitor minute changes in the distances between them in real time. If the distances increase, it means the mountain is "inflating."
2. Tiltmeters: This device acts like a super-sensitive level, measuring tiny tilts of the ground. Ground tilting due to mountain inflation is another critical signal.
Gas and Water Monitoring: Sniffing the Volcano's "Breath" Magma contains various gases (like sulfur dioxide, carbon dioxide, etc.). As magma nears the surface, these gases escape early through the crater or surface fissures. Scientists regularly collect air samples from the summit and foothills, analyzing changes in gas composition. A sudden spike in a key gas like sulfur dioxide is a very dangerous sign. Simultaneously, changes in the temperature and chemical composition of hot springs and groundwater on the mountain are important indicators.
Temperature Monitoring: Taking the Volcano's "Temperature" Using infrared thermal imagers on aircraft or satellites, scientists can map Mount Fuji's surface temperatures. An abnormal temperature rise in a specific area could signal a heat source (magma) rising below.

In essence, like a patient in an ICU, Mount Fuji is monitored around the clock and from all angles by these instruments. Any abnormality in the data is immediately detected and comprehensively analyzed.

So... Will Mount Fuji Erupt? And How Likely Is It?

The answer to this question has two parts.

First, a harsh but undeniable fact is: Mount Fuji will absolutely erupt again.

It is officially classified as an "active volcano," not a dormant one. Geologists widely agree it is currently "resting," not "retired." So, the crucial question is "when," not "if."

Then, how far away is this "when"?

A Warning from History: Mount Fuji's last major eruption was in 1707 (the Hōei eruption). It has been silent for over 300 years. Given its historical activity cycles, this "unusually long dormant period" is somewhat abnormal. Prolonged quiet often means energy is building up, potentially leading to a very large eruption next time.
A Potential Trigger: The massive 2011 Tōhoku Earthquake (March 11th) significantly impacted the tectonic plates under the Japanese archipelago. Research suggests this event may have increased pressure in the magma chamber beneath Mount Fuji – like shaking a soda bottle; even if you don't open it immediately, the pressure inside has built up.
Government Preparedness: The Japanese government takes this seriously. They have developed very detailed Fuji eruption evacuation plans, simulating potential volcanic ash distribution (which could reach as far as the Tokyo metropolitan area), and mapped out traffic control measures and evacuation routes. This plan involves evacuating hundreds of thousands of people, demonstrating that the official assessment identifies a real risk.

BUT! Important Note!

Are there currently definitive signs that an eruption is imminent? The answer is: Not yet.

While there have been some scattered signs (e.g., reports years ago of increased crater numbers or changes in groundwater chemistry in certain areas), those critical indicators mentioned earlier – such as widespread volcanic tremors, significant ground uplift, dramatic changes in gas composition – have not yet appeared.

To Summarize

Monitoring is Extensive: Scientists use every high-tech tool available to watch Mount Fuji like a closely monitored patient. No anomaly escapes their notice.
Eruption is Certain, Timing Unknown: Geologically, another eruption is inevitable. It's like a sleeping giant, currently resting uneasily.
No Need for Excessive Panic: Currently, there are no clear, strong signals pointing to an "imminent eruption." So, if you're planning a trip to Japan, there's no need to cancel your plans because of this. Should a real threat emerge, Japan's early warning system is designed to provide ample alert time.

Simply put, we can view Mount Fuji as a "time bomb," but scientists are scrutinizing the timer with a magnifying glass. For now, it appears that timer hasn't started ticking.

Hope this explanation helps!