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Mt. Fuji: Japan's sacred volcano

Is the recent tectonic activity around Japan a forewarning that Japan's largest volcano will blow? Probably not, explains volcanologist Erik Klemmeti.

Mt. Fuji (a volcano with more names than almost any other) in Japan is one of the most historically important volcanoes, possibly only rivaled by Vesuvius in its place in the mind's of people. In Japan, it is sacred, one of the three holy mountains of Japan, and visited frequently - one of the most popular hiking destinations on the planet with over 200,000 visitors a year. It can appear tranquil, but has a history that is more violent than the near-perfect stratocone (see top left) shape betrays.


Mt. Fuji is a product of the subduction zone that straddles Japan, with the Pacific Plate (to the north) and the Philippine Plate (to the south) subducting underneath the Eurasian plate. This is what drives the volcanoes and seismicity that occur so frequently in Japan, including volcanoes like Sakurajima, Kirishima, Unzen and, of course, Mt. Fuji.

Painting by Katsushita Hokusai of Mt. Fuji in the sunset.

The edifice of Fuji is huge. Looking at topographic relief maps (with some vertical exaggeration) of Honshu, the volcano dominates the southern region of the island. Fuji itself is over 3,700 meters / 12,000 feet tall (the tallest mountain in Japan) with a base that is 50 km in diameter. As with many large volcanoes, Fuji is actually the youngest of a number of volcanic systems that have been centered at this location - Komitake, Ko-Fuji (older) and Fuji (younger) - with scores of other vents pockmarking the flanks of the edifice. The oldest deposits in the Fuji complex are over 100,000 years old, but the modern edifice people associate with Fuji likely began growing ~11,000 years ago. The summit is dominated by a 500 meter crater that is almost 250 meters deep.

Fuji has experienced 16 eruptions since 781 A.D. - one of the more active in Japan, but quiet since ~1708. Sometimes the eruptions can be large - VEI 5 in 1707, 1050, 930 BC. Typically the eruptions are basaltic to andesitic, although the youngest Fuji is mainly basaltic. The early history of Fuji appears to be effusive, with extensive lava flows accounting for a quarter of the volcano's volume but sometime between 8,000 and 4,500 years ago the activity became more explosive - with a mix of larger explosive events and intermittent, smaller effusive eruptions. 

Map of the volcanic deposits of Mt. Fuji, Japan.

The 1707-1708 eruption is the one that has some people concerned about what Fuji might have in store. On October 26, 1707, Honshu was struck by a M8.4 earthquake and less than 2 months later, on December 16, 1707, Fuji began erupting. The initial eruption was explosive ash and puma, but within hours of starting the eruption became basaltic fountaining from a flank vent. Over the next few weeks, Fuji erupted ~0.68 km3 of material before the eruption ended at the start of 1708. The magma erupted during this eruption was decidedly mixed - from basalt to dacite - suggesting that it was fed by multiple magma sources. Ash from this eruption reached as far as Tokyo. If you look at the eruptive history of Fuji and the record of major earthquakes in Japan, you can see there isn't any real correlation between the two, so trying to connect the October 26, 1707 earthquake with the December 1707 eruption at Fuji is likely tenuous at best.

Since 1707, there hasn't been much activity at Fuji. Unconfirmed reports suggest a small eruption could have occurred in 1770 and 1854, but these dates should be treated skeptically. Since 2000-01, there have been a number of small earthquake swarms under Fuji, but many of the earthquakes are thought to be tectonic-related and (obviously) did not lead to an eruption. Some of these earthquake swarms were long-period events that are thought to be basaltic magma slowly recharging below Fuji, so the volcano is clearly not dormant. There has been the usual, speculative discussion of whether Fuji is "overdue" - a word you know I dislike. It clearly has been longer since the last eruption of Fuji in 1707 than in the centuries prior to the 1707 activity. However, again, trying to say that the volcano should behave predictably is not advised as there is speculation that the size of the 1707 eruption may have altered the geometry of the Fuji magmatic system. Most of the earthquakes under Fuji cluster to the northeast of the summit crater, so it is though that the magmatic system for Fuji lies there at depths between 10-20 km.

As you can imagine, with Fuji looming near Tokyo (within 100 km, depending on how you define both Tokyo and Fuji), there has been extensive work on volcanic hazards associated with the volcano (see below). The largest hazards come from ash and pumice from explosive eruptions, with some potential for basaltic pyroclastic flows and lahars. Lava flows are a threat as well, especially for areas close to the volcanic edifice (and dependent on the location of the vent). Another large VEI 5 explosive event at Fuji could deposit between 0.5-16 cm of ash on the Tokyo area, which would be a crippling blow to the city and any air traffic to/from the highly populated area of Honshu. However, even with Fuji being so quiet as it has been since 1708, the cities around Fuji are prepared for new eruptions. However, it is most likely, based on the eruptive history of Fuji, that any new eruption will be small.

Volcanic hazard map and information for Fuji in Japan (in Japanese). Click here to see large version

Mt. Fuji is clearly both a beautiful and dangerous volcano. However, there is little beyond anecdotal evidence that large earthquakes in Japan will cause Fuji to erupt. Even after this week's M9.0 earthquake and an earthquake located in the area of Fuji, there is no reason to have immediate concern about the volcano erupting - think of this like the Japanese version of the "concern" that Katla would erupt after Eyjafjallajokull's activity in 2010 (mostly coming from misinformed media and the apocalypse-loving crowd). So far, Fuji has not shown any of the signs of renewed activity, such as harmonic tremors or tornillos, with earthquakes starting deep and becoming shallower with time or increasing volcanic gas emissions - it remains tranquil. This does not mean that we should not keep an eye on Fuji (it definitely has many, many webcams pointed towards it) and be prepared because it is still clearly an active volcano. Fuji should be seen as a symbol of strength for a nation recovering from disaster, rather than another harbinger of doom.

Selected references:

Watanabe, S., et al., 2006. The evolution of a chemically zoned magma chamber: The 1707 eruption of Fuji Volcano, Japan. Journal of Volcanology and Geothermal Research, v. 152, p1-19.

Yamamoto, T., et al., 2005. Basaltic pyroclastic flows of Fuji volcano, Japan: characteristics of the deposits and their origin. Bulletin of Volcanology, v. 67, p622-633.

Yoshimoto, M., et al., 2004. Multiple magma reservoirs for the 1707 eruption of Fuji volcano, Japan. Proceedings of the Japan Academy, Series B, v. 80, p103-106.

Live today! Unfiltered lessons of a female entrepreneur

Join Pulitzer Prize-winning reporter and best-selling author Charles Duhigg as he interviews Victoria Montgomery Brown, co-founder and CEO of Big Think, live at 1pm EDT today.

Two MIT students just solved Richard Feynman’s famed physics puzzle

Richard Feynman once asked a silly question. Two MIT students just answered it.

Surprising Science

Here's a fun experiment to try. Go to your pantry and see if you have a box of spaghetti. If you do, take out a noodle. Grab both ends of it and bend it until it breaks in half. How many pieces did it break into? If you got two large pieces and at least one small piece you're not alone.

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Two-thirds of parents say technology makes parenting harder

Parental anxieties stem from the complex relationship between technology, child development, and the internet's trove of unseemly content.

Sex & Relationships
  • Today's parents believe parenting is harder now than 20 years ago.
  • A Pew Research Center survey found this belief stems from the new challenges and worries brought by technology.
  • With some schools going remote next year, many parents will need to adjust expectations and re-learn that measured screen usage won't harm their children.

Parents and guardians have always endured a tough road. They are the providers of an entire human being's subsistence. They keep that person feed, clothed, and bathe; They help them learn and invest in their enrichment and experiences; They also help them navigate social life in their early years, and they do all this with limited time and resources, while simultaneously balancing their own lives and careers.

Add to that a barrage of advice and reminders that they can always spend more money, dedicate more time, or flat-out do better, and it's no wonder that psychologists worry about parental burnout.

But is parenting harder today than it was, say, 20 years ago? The Pew Research Center asked more than 3,600 parents this question, and a majority (66 percent) believe the answer is yes. While some classic complaints made the list—a lack of discipline, a disrespectful generation, and the changing moral landscape—the most common reason cited was the impact of digital technology and social media.

A mixed response to technology

children using desktop computer

Parents worry that their children spend too much time in front of screens while also recognizing technologies educational benefits.

(Photo: Chris Hondros/Getty Images)

This parental concern stems not only from the ubiquity of screens in children's lives, but the well-publicized relationship between screen time and child development. Headlines abound citing the pernicious effects screen time has on cognitive and language development. Professional organizations, such as the American Academy of Child and Adolescent Psychiatry, issue warnings that too much screen time can lead to sleep problems, lower grades, weight problems, mood problems, poor self-image, and the fear of missing out—to name a few!

According to Pew's research, parents—which Pew defines as an adult or guardian with at least one child under their care, though they may also have adult children—have taken these warnings to heart. While 84 percent of those surveyed are confident they know how much screen time is appropriate, 71 percent worry their child spends too much time in front of screens.

To counter this worry, most parents take the measured approach of setting limits on the length of time children can access screens. Others limit which technologies children have access to. A majority of parents (71 percent) view smartphones as potentially harmful to children. They believe the devices impair learning effective social skills, developing healthy friendships, or being creative. As a result, about the same percentage of parents believe children should be at least 12 years old before owning a smartphone or using social media.

But a deeper concern than screen time seems to be what content those screens can access. An overwhelming 98 percent of those surveyed say parents and guardians shouldered the responsibility of protecting children from inappropriate online content. Far less put the responsibility on tech companies (78 percent) or the government (65 percent).

Parents of young children say they check the websites and apps their children use and set parental controls to restrict access. A minority of parents admit to looking at call and text records, tracking their child's location with GPS, or following their child on social media.

Yet, parents also recognize the value of digital technology or, at least, have acquiesced to its omnipresence. The poster child for this dichotomy is YouTube, with its one billion hours played daily, many before children's eyes. Seventy-three percent of parents with young children are concerned that their child will encounter inappropriate content on the platform, and 46 percent say they already have. Yet, 80 percent still let their children watch videos, many letting them do so daily. Some reasons cited are that they can learn new things or be exposed to different cultures. The number one cited reason, however, is to keep children entertained.

For the Pew Research Center's complete report, check out "Parenting Children in the Age of Screens."

Screens, parents, and pandemics

Perhaps most troubling, Pew's survey was conducted in early March. That's before novel coronavirus spread wildly across the United States. Before shelter-in-place laws. Before schools shuttered their doors. Before desperate parents, who suddenly found themselves their child's only social and educational outlet, needed a digital lifeline to help them cope.

The COVID-19 pandemic has led many parents to rely on e-learning platforms and YouTube to supplement their children's education—or just let the kids enjoy their umpteenth viewing of "Moana" so they can eke out a bit more work. With that increase in screen time comes a corresponding increase in guilt, anxiety, and frustration.

But are these concerns overblown?

As Jenny Radesky, M.D., a pediatrician and expert on children and the media at the University of Michigan's C.S. Mott Children's Hospital, told the New York Times, parents don't always need to view screen time as a negative. "Even the phrase 'screen time' itself is problematic. It reduces the debate to a black and white issue, when the reality is much more nuanced," Radesky said.

Radesky helped the American Academy of Pediatrics craft its statement about screen time use during the pandemic. While the AAP urges parents to preserve offline experiences and maintain limits, the organization acknowledges that children's media use will, by necessity, increase. To make it a supportive experience, the statement recommends parents make a plan with their children, be selective of the quality of media, and use social media to maintain connections together. It also encourages parents to adjust their expectations and notice their own technology use.

"We are trying to prevent parents from feeling like they are not meeting some sort of standard," Radesky said. "There is no science behind this right now. If you are looking for specific time limits, then I would say: Don't be on it all day."

This is good advice for parents, now and after the pandemic. While studies show that excessive screen time is deleterious, others show no harm from measured, metered use. For every fear that screens make our kids stupid, there's a study showing the kids are all right. If we maintain realistic standards and learn to weigh quality and quantity within those standards, maybe parenting in the digital age won't seem so darn difficult.

How meditation can change your life and mind

Reaching beyond the stereotypes of meditation and embracing the science of mindfulness.

Videos
  • There are a lot of misconceptions when it comes to what mindfulness is and what meditation can do for those who practice it. In this video, professors, neuroscientists, psychologists, composers, authors, and a former Buddhist monk share their experiences, explain the science behind meditation, and discuss the benefits of learning to be in the moment.
  • "Mindfulness allows us to shift our relationship to our experience," explains psychologist Daniel Goleman. The science shows that long-term meditators have higher levels of gamma waves in their brains even when they are not meditating. The effect of this altered response is yet unknown, though it shows that there are lasting cognitive effects.
  • "I think we're looking at meditation as the next big public health revolution," says ABC News anchor Dan Harris. "Meditation is going to join the pantheon of no-brainers like exercise, brushing your teeth and taking the meds that your doctor prescribes to you." Closing out the video is a guided meditation experience led by author Damien Echols that can be practiced anywhere and repeated as many times as you'd like.
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