A volcano slides into the sea causing an 800 foot wave to crash onto into an adjacent island. As that wave crashes onto land it 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 have significant impacts on 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.” These are boulders that 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 the boulders in our who-done-it are found on an a small island that has never experienced glaciation. Like erratics, though, these boulders are clearly out of place. They are composed of rock unrelated to immediate ground they sit upon nor are they similar to any rock found at higher ground. So if they didn’t erode in-place or roll down from higher ground where did they come from?
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? Researches speculated that they must have been pushed up from below 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 composed of single 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.
This is a very interesting hypothesis for these out-of-place boulders, but is there additional evidence to back up 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, could they determine when the megatsunami happened? 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 70,000 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:
Tsunami-deposited boulders and the Young Earth Creationist’ timeline
These boulders are just another in a endless list of geological features that the flood geology model of Young Earth Creationists (YECs) fails to explain. These boulders also 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.
However, even YECs are unlikely 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 must be less than 4350 years (the date of Noah’s Flood) old. The large 10,000 foot tall volcano that created the tsunami had to form after 4350 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.
In the YEC timeline, the volcano must 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. How then do YEC explain the extent of that alteration which suggests at least 70,000 years of cosmogenic radiation was necessary to produce the observed products? 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 many object know to be at least 4000 year old 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 within the purview of 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? It can’t be because there are any eyewitnesses or because the Bible records this historical event. Rather they will agree because the circumstantial evidence is so strong. Hence, despite protestations about historical science they do accept many of the conclusions of historical scientific studies. However, when it comes to the determination of the date for which this historical event occurred they will claim that the dating method is a form of historical/origins science and can’t be trusted.
The strength of the evidence for the age of the boulders and the means by which the rocks got to their current positions are well established but the YEC can’t accept the ages so they will denounce the date of origin while readily accepting the conclusions of historical science that a large tsunami is responsible for moving these boulders up the side of a mountain.
To read more about this tsunami:
Omira, Rachid, Rui Quartau, Inês Ramalho, Maria Ana Baptista, and Neil C. Mitchell. “The Tsunami Effects of a Collapse of a Volcanic Island on a Semienclosed Basin: The Pico‐São Jorge Channel in the Azores Archipelago.” Plate boundaries and hazards 219 (2016): 271-287.