Dr. Moshier Part 2

Here is the second installment of Dr. Moshier's blog reprinted with permission. Enjoy!

Blog Entry: The big one that got away (posted July 6, 2009)

Ashkelon is a city on the coast. There is a casual “beach town” vibe here that is not much different from places in the USA like Corpus Christi or Ft. Lauderdale. During the weekends (Friday-Saturday) the population of Ashkelon must triple, at least the occupancy of our hotel does.

Of course, there are disadvantages to living along the coast. The beaches of Corpus Christi and Ft. Lauderdale are frequently traumatized by hurricanes. But, such violent storms are not spawned in the warm waters of the Mediterranean; it’s just not big enough and lies too far north of the equator for strong cyclonal patterns to develop. Other dangers lurk in this tectonically active region that can result in devastation to the Mediterranean and Aegean coasts. Something really catastrophic happened here about 3600 years ago.

In the Aegean Sea between southern Greece and western Turkey, and due north of the Island of Crete there is a crescent-shaped island (or rather strand of small islands) named Santorini, also known as Thera. The Minoan culture was thriving in this region during the Late Bronze Age. Minoan art and ceramics are colorful and sophisticated. There may be cultural and ethnic connections between the Minoans and other people groups scattered around the Western Mediterranean, such as the Philistines, Phoenicians, Hyksos, etc. But Minoan culture basically ended with a bang when Thera blew up. Thera is a giant volcano. Or was.

So much ash was pushed up into the atmosphere that it probably explains evidence of climate disturbances in China and frost damage to trees in California and Ireland (Science v. 312, p. 548). Ash from the eruption has been recovered in Greenland ice cores and sediment cores in the Nile Delta. A little global cooling was the least of worries for people living along the Mediterranean and Aegean coasts. The eruption resulted in the collapse of the center of the island creating a caldera and surges of pyroclastic material flowed in to the surrounding sea. The displacement of water produced the dreaded tsunami waves that propagated in every direction.

Even some 500 km away, the coast of Israel could not have been spared of this disaster. Computer models show the waves hitting our Late Bronze city of Ashkelon about 100 minutes after those pyroclastic surges hit the ocean floor. With wavelengths of over 100 km, tsunami waves build in height as they run up on coastlines. Waves hitting the Levant could have been up to 12 m above sea level. Surely Ashkelon was smacked, but what actually happened and can we find evidence of that fateful day of doom?

Finally, there is controversy over the date of the eruption. Geochronologists using carbon-14 date the eruption at about 1600-1620 BC. Archaeologists, particularly those working Bronze Age sites in the Nile Delta and Levant, believe the archaeological indicators and chronologies put the date at 1500 BC!

Henrik Bruins, a geochronologist at Ben Gurion University of the Negev, has been looking along the coast of Israel for deposits that might be linked to the Thera eruption. He has described in great detail Thera tsunami deposits on the Island of Crete. In the spring of 2009, Ashkelon Excavation Director Daniel Master and Dr. Bruin discussed the possibility of tsunami deposits at Ashkelon. Daniel recalled a particular massive sandy layer on top of the hard kurkar dune rock along the beach cliff. It is about 6 m above present sea level. Perhaps if this deposit had the characteristics of a tsunami deposit and contained datable material and diagnostic pottery, we could establish the presence of the tsumani at Ashkelon and contribute to the resolution of the debate over the timing of the eruption.

My very first morning here two weeks ago we looked at that bed (we could not reach it due to its position on the cliff) and made plans to clean it up for study. What that means is that daredevil archaeologist Josh Walton would scale a ladder and chisel out a smooth surface with a pick and trowel. That did not happen until this past Sunday after our drilling project was finished. It took two hours hard labor by Josh and my geoarchaeology student assistant Ben before I had my first look at the deposit. Josh had already determined that the pottery beneath and within the deposit was much later than Bronze Age. I could see no evidence that the bed was anything other than typical tell sediment (thebrownish yellow loam soiling all my T-shirts). Shoot.

We decided to comb the beach cliff for other candidate deposits, using information from a previous geoarchaeological survey. About 250 m north of the disappointing deposit we found an old covered trench that was documented to contain, “fluvial sand” with Chalcolithic and Early Bronze pottery. Fluvial infers water deposition. The geologist who had described the trench wondered if flooding on the tell had resulted in the deposition of sand in narrow channels running toward the sea. It is hard to imagine that enough rainwater could collect on the tell to create such a torrent. It made sense to us that “the flood” may have been from run up or back wash from the big one. So this morning, Josh and Ben were at it again with pick and trowel, only this time they did not need a ladder. They cleaned a 4 m section and dug a 2.5 m trench. We found nothing even remotely similar to the previous description of that level (in all fairness, we might not have been in exactly the same place described in the previous report). We see no other reasonable places to look for evidence of the elusive tsunami deposit. I joked with Josh and Ben, “there goes our article in Nature.” Josh was not sure if his hours of digging would even have been acknowledged, anyway. Because they worked so hard to create a nice clean trench, we dedicated the next hour to describing the 4 m of sediment in detail, just for the record.

Even though we don’t have geological evidence for the tsunami does not mean that ancient Ashkelon was spared. From now on, archaeologists digging levels of Bronze Age occupation will be mindful to look for evidence of natural destruction. Our work to create a “bedrock” map of the tell will be used to model the effects of a wave on reconstructed Early Bronze Age topography. If waves were even as much as 12 m high hitting the coast, either as a wall or rapidly rising water, we know that some Bronze Age levels are as high as 17 m above present sea level. Even better for them, sea level during the Bronze Age was about 2 m lower than present! The ancient citizens of Ashkelon would have certainly been terrified by the giant wave or waves soaking the coast, but many may have survived by virtue of the elevation provided by the old kurkar dune beneath their city. They probably had more to fear from the falling ash. Who knows what human or natural activity might have erased physical evidence of the event? Or, have we looked in all the right places?