# Mt. Fuji Erupts. Is Tokyo Screwed?

**URL:** <https://boards.straightdope.com/t/mt-fuji-erupts-is-tokyo-screwed/516060>\
**Category:** Factual Questions\
**Created:** [November 2, 2009, 4:08pm UTC](https://boards.straightdope.com/t/mt-fuji-erupts-is-tokyo-screwed/516060 "2009-11-02T16:08:22Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![HeyHomie](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/heyhomie/32/207_2.png) [@HeyHomie](https://boards.straightdope.com/u/HeyHomie)\
**Post date:** [November 2, 2009, 4:08pm UTC](https://boards.straightdope.com/t/mt-fuji-erupts-is-tokyo-screwed/516060/1 "2009-11-02T16:08:22Z")

</div>

Pretty straightforward, really: If Mt. Fuji were to erupt on a similar scale to its last known eruption in 1700-something, what’s the outlook for Tokyo?

---

<div class="post-metadata">

**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\
**Post date:** [November 2, 2009, 4:29pm UTC](https://boards.straightdope.com/t/mt-fuji-erupts-is-tokyo-screwed/516060/2 "2009-11-02T16:29:35Z")

</div>

From Wiki, here’s [map of the ashfall](http://upload.wikimedia.org/wikipedia/commons/3/31/Volcanic-ash-downfall_map_of_Mt.Fuji_Hoei-eruption01.jpg) from the Hoei eruption in 1707. It looks like downtown Tokyo (the big pink area in the center of the map) gets between one and two centimetres of ash; the effects would be similar to Mt. St. Helen’s 1980 eruption, only with ash falling on the world’s largest city instead of eastern Washington State. Yokohama (the smaller pink area to Tokyo’s south) gets about six inches, which might be more problematic.

---

<div class="post-metadata">

**Author:** ![HeyHomie](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/heyhomie/32/207_2.png) [@HeyHomie](https://boards.straightdope.com/u/HeyHomie)\
**Post date:** [November 2, 2009, 4:37pm UTC](https://boards.straightdope.com/t/mt-fuji-erupts-is-tokyo-screwed/516060/3 "2009-11-02T16:37:35Z")

</div>

Yes, but what about toxic fumes, pyroclastic (sp?) flows, etc.? Is Tokyo far enough away that this isn’t a concern?

---

<div class="post-metadata">

**Author:** ![pan1](https://avatars.discourse-cdn.com/v4/letter/p/e495f1/32.png) [@pan1](https://boards.straightdope.com/u/pan1)\
**Post date:** [November 2, 2009, 8:15pm UTC](https://boards.straightdope.com/t/mt-fuji-erupts-is-tokyo-screwed/516060/4 "2009-11-02T20:15:07Z")

</div>

> [@HeyHomie](#):
>
> Yes, but what about toxic fumes, pyroclastic (sp?) flows, etc.? Is Tokyo far enough away that this isn’t a concern?

Fumes are a concern. But it would take a worst case scenerio for the air to become deadly in Tokyo. (beyond avoiding inhaling ash)

Pyroclastic flows are not a concern.

---

<div class="post-metadata">

**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\
**Post date:** [November 2, 2009, 8:26pm UTC](https://boards.straightdope.com/t/mt-fuji-erupts-is-tokyo-screwed/516060/5 "2009-11-02T20:26:47Z")

</div>

> [@MikeS](#):
>
> .. the effects would be similar to Mt. St. Helen’s 1980 eruption, only with ash falling on the world’s largest city instead of eastern Washington State.

Actually, the 1980 eruption of Mount St. Helens [had measurable ash in twelve states](http://www.pnsn.org/OUTED/VIRTTOURS/VIRTTOURPICS/may18_ashmap.gif).