Sunday, January 24, 2010

Core Sampling Project

As promised, here is the first two of Dr. Moshier's blogs reprinted with permission.

Blog Entry: A big pile of sand (posted July 1, 2009)

All of my T-shirts have brown stains on the part over my belly. The hotel laundry just can't wash out the silt and clay that we are drilling out of Tell Ashkelon. I think the size of the stain is proportional to the size of the belly, a theory confirmed by a quick look at individuals in the pottery compound. I think I’ll have salad tonight for dinner.

The dirt doesn't seem to show as much on my pants, as they are very pale brown to begin with, a shade close to 10YR7/4 on the Munsell scale of soil colors. My typically pale “white” skin color is changed, too, either due to the sun or the absorption of Holy Land clay into my pores. Sunscreen only serves to give the clay something to stick to. Even after rigorous scrubbing in the shower, mud still smears the towel.

On Monday we started a second round of drilling. Archaeology students Ben and David assisted me again. Our driller Efni showed up at the park with his rig at 7 AM. We had been there since 5 AM. Efni packs up and leaves at 3PM and there is no time for lunch before he leaves. Our strategy Monday morning was to push up close to some of the excavation sites. The archaeologists know that the Middle Bronze settlement is built on a cover of yellow sand that extends beyond the (safe) level of excavation. Is the sand part of a dune that covers older cultures? We really wanted to punch through that sand to find out.

The drill is called a bucket auger that looks like a medium-size garbage can with jaws. The rig is mounted on a large tractor that is part forklift and part bulldozer. The drill string rotates and lengthens like a radio antenna, as the bucket churns down through the sediment. It is strong enough to grind through soft rock like the local sandstone, but the scraping sounds like fingernails on a blackboard and louder than a dinosaur in Jurassic Park. When the bucket is full with about 30 to 40 cm of sediment, the drill string is retracted and the bucket returns to the surface. The driller mechanically shakes the sediment out of the bucket, which falls on the ground for examination and sampling.

If everything goes well we can reach a total depth of 11 meters below the surface. Things did not go well Monday morning. At about five meters depth we encountered the yellow sand, but the sand was dry and started caving into the hole. We typically have to pour one or two standard buckets of water down the hole every time the auger goes down in dry sand. The water gives the sand cohesion and conditions the side of the hole to prevent caving. The idea of pouring fresh water down a dry hole seems ironic and perverse. It just did not work and we never got deeper than six meters. We moved the rig about 4 m to the side and tried again with the same results. If there is if there is older archaeological material beneath the sand, we will have to find a better method of drilling to find it. Next, we moved to another location near an excavation site. Same thing. Dry caving sand. Excavation Director Daniel Master stopped by to hear my complaints and told me, “Tell Ashkelon does not easily give up its secrets.”

The last three probes on Monday were more successful. We drilled in the main parking lot located between the north and south tells. The lot was probed in the 1980s but the reports from that survey are difficult to interpret because the descriptions are ambiguous and the depths don’t seem correct. We have good data now and that is the important thing. Even if I offer a lousy interpretation, I want our descriptions of the material and stratigraphy to be useful to future scholars working here.

On Tuesday we started by drilling very close to the beach cliff next to the south rampart built by Crusaders. The goal is to trace deposits evident on the beach cliff landward. Drilling was painfully slow through the sand. David and Ben carried gallons and gallons of water (uphill) from a park faucet some 50 m away from the drill sites. At about 9 AM the cable on the drill rig snapped. Efni called someone to come with a new cable. We were down for about 30 minutes. I fell asleep in the shade sitting up with my legs crossed on the ground. It was hot, but we had a constant breeze from the sea.

The next probe turned out to be our last of the season. It took nearly four hours to drill 10.4 m. We needed lots of water to get through the sand. David and Ben got quite a workout carrying jerry cans of water from an irrigation tap David found about 75 m from the drill site. I wanted to find a place where we would drill to bedrock. We have all assumed that hard sandstone, called kurkar, underlies the tell because it is exposed to elevations of up to 18 m above sea level. But, we have never encountered hard sandstone in our course landward under the tell. We do encounter lots of sand (remember the dry yellow sand from Monday?). We should have reached hard rock in our first probe near the south rampart beach cliff, but we did not. So for this probe we moved the rig to the north tell and set up near the cliff face (about as close as we could safely put it). We should have reached hard rock there, but again we did not! So it appears that the hard rock only occurs along the beach cliff. Hypothetically, the ancient sand dunes that formed the original topography of the tell were only cemented in this narrow zone against the sea. Seawater contains the dissolved calcium and carbonate that probably cemented the rock. We find no other obvious source of rock for the crusader ramparts and structures than the area of the beach cliff and a small quarry close to the cliff on the north tell. It seems then, when we encounter yellow sand anywhere under the tell, we are at, or near, the level of the original topography of the tell. Ashkelon appears to be built on a pile of sand. Our drilling efforts have provided the data to reconstruct the original topography of the site before human habitation and modification of the land.

We did not always encounter what we expected (that would be too easy). But perhaps Tell Ashkelon is beginning to reveal some of its geological secrets after all.

Read more from Dr. Moshier and his team next time to learn more about how geology is contributing to the archaeological exploration of ancient Ashkelon.

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