Higher Ground

While browsing through the channels yesterday, I happened upon Deep Impact on one of the channels and because I love all things disaster related, I kept it on in the background while I worked.  As the movie progressed through the various stages of calamity toward the first mini-climax,  I found myself wondering how far a tsunami wave generated by a meteor strike could travel.  And most importantly, if a strike off the Atlantic Coast would pose a threat to us up here on our mountain.  After all, threat assessment and mitigation is kind of what I do.  So, off to the internet I went.

What I mostly learned is that the only kind of tsunami us New Englanders really need to fear is one generated by space rocks.  The lack of geological attributes that keeps us free of most earthquakes also makes it unlikely that an earthquake-created tsunami would reach us here.  I also learned that if there isn’t a good chance something might happen where you are, it isn’t likely that people have spent time and money figuring out what would happen if it did.  Fair enough!

But, because I am all about Plan B, I had to know.  So my tsunami search began.  Here are some of the helpful facts I learned in my search.

  • Tsunami’s generally require an earthquake in excess of 8.0 on the richter scale, a massive landslide (above  and into or under water), or the aforementioned space rocks.
  • Tsunami waves that result from tectonic activity can reach 100’s of feet in height as they approach the shoreline.  Mega tsunamis that generate waves as the result of landslides and impact events have been recorded to reach 1700 feet in height.  Estimates of some historical impact waves go as high as 1+miles.
  • Tsunami waves are traveling incredibly fast, 600 mph, which is as fast as many airplanes travel.
  • While the initial impact of a tsunami is devastating to the area of inundation (the distance inland the wave travels), that is not the end of the problems it causes.  Tsunamis have an equally devastating aftermath as they poison the groundwater, freshwater, and even the land they traverse with high concentrations of salt.  This creates an environment rife with starvation and disease.

But, did I find the answer to my question regarding the safety of my family up here atop my mountain?  Kind of.

We are roughly 40 miles from the ocean as the crow flies and just over 1000 ft above sea level.  I am reasonable confident that there are few circumstances that would result in a regular tsunami wave reaching us here.  But…because of the movie, I wanted to know the big question – if an asteroid strike occurred off the coast of New England, would we still be safe – at least from the initial impact and resulting mega-tsunami.

Because no one in my house is a tsunami expert or a geologist or really any kind of mathematician or scientist, the science and math part of this may be a bit on the fuzzy side.  I roped my husband into helping as he is more math-minded than me and so that I can blame any errors on him.

We thought it would be easy to figure out how big of a wave it would take to make its way all the way here.  Unfortunately, it isn’t as simple as some math formula and guesswork.  I understand now why there is so much “modeling” used in tsunami forecasting.  There also isn’t alot of hard data – certainly not any relating to the size impact we were interested in.  But we did the best we could.

Here goes.

The 1958 Lituya Bay Tsunami in Alaska had the largest wave ever recorded at 1720 ft.  It traveled about 3600 ft inland over mountainous terrain.  The most recent tsunami this past March in Japan had a top wave height of just over 100 ft. and it traveled almost 6 miles inland over relatively flat land.  Elevation and terrain-wise, we live somewhere between these two extremes.  The estimated wave heights of the mega tsunami generated by the impact that created the Chicxulub Crater in Mexico is just under 2 miles high.  And now….some math-estimating.

If we use the 2 mile wave height as a baseline and ramp up the numbers for the Lituya Bay tsunami for comparison, we need to scale everything up by 6x.  This means that over mountainous terrain, a 2 mile high wave might travel roughly 4 miles inland.  Because the terrain between here and the coast is not as mountainous as Alaska, we have to account for the difference.  To be on the safe side, we opted to multiply that 4 miles by the 6 miles from the Tōhoku Tsunami in Japan for a total of about 24 miles inland.

Since we are more than 40 miles from the coast, even with the fuzzy math, it seems like we would at least be safe from the waves if a giant space rock plunged into the ocean just to our east.

That settled, now I need to determine what it might take to make it though the nuclear winter with a side of super-acid rain that comes after the space rock.  But that is a topic for another day.

Don’t be scared, be prepared.