Local Catastrophes Happen: Mega-Tsunami Moves 700-Ton Boulders Uphill

A volcano slides into the sea causing an 800 foot wave to crash onto into an adjacent island. That wave picks up 700-ton boulders and throws them uphill leaving them stranded far above their source.   It sounds like a plot from a Hollywood movie but this is real.  It happened in the Cape Verde Islands off of the west coast of Africa long ago.

Yes, local geological catastrophes happen and those catastrophes can alter the landscape.   In a geological who-done-it, huge boulders found on an otherwise relatively flat surface on a remote island begged the question: how did they get there?

If these were found in Wisconsin we might label these boulders “erratics” indicating they were rocks that had hitched a ride on the huge ice sheets that once flowed down from the north. When the ice retreated it left massive rocks scattered over the surface.   But these boulders are found on an island that has never experienced glaciation.  Like erratics, though, these boulders are clearly out of place. They are composed of rock unlike the immediate ground they sit upon and are not like rock found at higher ground. So if they didn’t erode in-place or roll down from higher ground where did they come from?

The tsunami generated by Fogo's collapse apparently swept boulders like this one from the shoreline up into the highlands of Santiago island. Here, a researcher chisels out a sample. Image credit: Ricardo Ramal

The tsunami generated by Fogo’s collapse apparently swept boulders like this one from the shoreline up into the highlands of Santiago island. Here, a researcher chisels out a sample. Image credit: Ricardo Ramal

They came from below. These boulders are composed of volcanic material along with marine limestone. Rock of similar composition is found well below these boulders’ current location.  If that rock from below is the source of these boulder then how did they come to be over 500 feet or more above sea level?  One hypothesis left is that they must have been pushed up there by some force.  In this case, that force was a giant tsunami.

Looking 30 miles across open ocean there is another island.  That island is one large volcano and you can see from the Google map below (zoom in on the left side island) that this volcano has all the appearance of having collapsed in the past. That collapse would have sent a wall of water toward the very location where these boulders are found.

It seems like a great hypothesis, but is there additional evidence to back of that conclusion? Yes!  Geologists set out to test this idea by dating the boulders to see when they came to be at their current positions.  In other words, when did this megatsunami happen?  By using a form of dating called cosmogenic dating they were able to estimate that these boulders had been sitting in their current positions for about 73,000 years. That dates fit within the dates, derived by several types of measures, for when the volcano had a catastrophic collapse. The overlapping dates for the collapse and the length of time these boulders have been lying in their present position is compelling evidence that these boulders were brought to the present location by a tsunami.

The dating methods and the geological story and described in this very informative video linked to below:

<p><a href=”https://vimeo.com/119311104″>RISING ISLANDS, MONSTER WAVE</a> from <a href=”https://vimeo.com/ei”>Earth Institute</a> on <a href=”https://vimeo.com”>Vimeo</a&gt;.</p>

Tsunami-deposited boulders and the Young Earth Creationist timeline

These boulders are just another in a long list of geological features that the flood geology model of Young Earth Creationists (YECs) fails to explain.  These boulders also clearly demonstrate that local catastrophic events can occur that cause rapid changes to the Earth’s surface.  YECs  frequently point to features to geological features and say that catastrophic events must have caused them and then imply or explicitly state that therefore there must have been a global flood as if only a global flood could be responsible for such features.

In this case, even YECs are not likely to invoke a global flood to explain these boulders and will probably accept that these are the result of a localized catastrophic event.

Why? Because these boulders are of volcanic origin. The islands are volcanic in origin and have no sedimentary flood deposits on them.  Thus in the YEC timeline these islands and the boulders on them are all less than 4250 years old.  The large 10,000 foot tall volcano that created the tsunami had to form after 4250 years ago and then experience a large collapse.  The boulders that the wave ripped from the rock face and tossed up on the plains where then exposed to the solar (cosmogenic) radiation which caused elements in its newly exposed surface to be altered.  That extent of that alteration suggests some 73,000 years of cosmogenic radiation was necessary to produce the observed products.  In the YEC timeline, the volcano would have been formed in just a few hundred years and then caused the tsunami but then the boulders would only have been exposed to cosmogenic radiation for less than 4000 years.  To explain the amount of radiation measured they would have to propose vastly greater amounts of radiation in the past than the present but we have plenty of objects of known 4000 year old age that show no evidence of greater radiation levels at that time.

Historical science or observational science?  YECs try to make a hard distinction between the two, claiming that historical or “origins” science can’t be trusted because no one was there to witness the event and these events can’t be tested by repeating the experiment.  Yes, our investigation of these boulders is generally what we would call historical science.  However, I suspect that no YEC is going to deny that these boulders are likely the result of a tsunami and they will probably agree that it was caused by a landslide on an adjacent island. Why will they agree? Not because there are any eyewitnesses nor because the Bible records this historical event. Rather they will agree because the circumstantial evidence is so strong. However, when it comes to when this occurred they will claim that dating is historical/origins science and can’t be trusted.  The evidence really is no less convincing but they can’t accept the ages so they will denounce the dates while accepting the conclusions of historical science that a tsunami did happen.


  1. Thanks for this post, this was new information for me (both the local boulder/volcano and the principle of cosmogenic radiation)

    I’m not familiar enough with official flood geology theories, esp about volcanic islands, to know if they would claim them post-Flood or simply created with the Earth and suggest explanations for the lack of sedimentary deposits, etc. In my experience the layman thinking tends to simply be “lots of water and force could do lots of things so who am I to say it couldn’t have produced Evidence X Y or Z…”


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