Archaeology in a Whole New Dimension

By Victoria Pagano

Hello again, it’s Victoria here to tell you that I’m excited. Excited about the work we’re doing out here in Eagle Cave and with the ASWT project as a whole. Now this is not to say that I wasn’t enthusiastic when I first found I would get a chance to intern in an amazing place, with knowledgeable people, learning and doing great new things; but, I’m writing now with a little training under my belt as to the way things work and and a better understanding of how absolutely fantastic it really is.

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Okay, this isn’t at Buenavista, but it is one of the sites that is worked on by the project. Mighty “El Castillo” at Xunantunich, just one example of the architecture and archaeology to be found in Belize.

Before ASWT

First, I would like to tell you a bit about my first and only field work in archaeology…just to offer a bit of perspective. I was unbelievably lucky to work in Belize. A beautiful country full of cultural and ecological diversity– not to mention the incredible historical and archaeological richness it holds as well. The project was based in the Mopan River Valley, studying the ancient Maya sites of San Lorenzo, Xunantunich, and Buenavista del Cayo. My work was focused at Buenavista, a mid-level city center with plazas and stone structures that had been reclaimed by the jungle.

Belize

That’s where I worked, Buenavista del Cayo. Just down the river from Xunantunich and many other archaeological sites.

It was in Belize that I learned basic excavation procedures:

Step 1: Find somewhere you want to excavate and establish an excavation unit. This includes (for most) establishing a permanent datum, laying out the unit, and taking starting measurements.

Step 2: Establish your excavation protocol. Are you going to follow natural breaks in the stratigraphy, or are you going to use an arbitrary measurement to create your strata, lots, layers, etc. You’ll probably want to sketch and photograph the starting and ending surfaces, too, as you work your way down.

Step 3: You find something really cool in the floor or wall of your unit… a hearth, post-hole, projectile point, a body, etc. — you decide you want to make sure this is in your notes (hopefully you are taking notes, good notes), so you need to take additional steps.

Step 4-6: You need to 4) Take photographs— with a scale and some indication of direction 5) Map it i.e. create a drawing by measuring to and from objects in your unit to an established point or points, like a sub-datum. This will yield a plan or profile map with detail as to where your find is and where everything else in your unit is in relation to your find. Detail, detail, detail!  Depending on how precise you want your map to be, if you have help, and your level of OCD, drawing a map can take anywhere from minutes to hours.  6) Take more notes of the object’s location, this may include a GPS point that you tie to your datum later, or measurements that you will use to associate the object’s location relative to the datum.

Step 7: You’re probably pretty tired from all those steps you took to draw your unit. You need a nap, but chin up, you established your unit today AND you found something! Hopefully your notes are good, you read that compass properly, and you’re mapping skills are adequate enough that your map doesn’t simply look like a box with a few misshapen circles, squiggly lines, and a triangle.

Now I have nothing against all those steps (the old fashioned paper and pen method works), but there is always room for improvement.  So why is it I am so ecstatic to work in a place where there isn’t monumental architecture, elaborate burials, mysterious mythology and codices? Structure from Motion.

What is Structure from Motion?

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Here I am focused on photographing my unit for SfM.

Structure from Motion (SfM) is a surprisingly simple technique that is easy to learn, quick to do in the field, and potentially available to archaeologists wherever they work, or at least those with access to modern technology. SfM uses still-motion photography to rebuild real-world, dimensional objects. Using a digital camera you take a series of overlapping, sequential photographs of your desired target and run them through a software program, such as Agisoft Photoscan.  The software is able to match up all the different photographs and build a virtual 3D model of the target (for more info on what Structure from Motion is, see our blog post from last spring:  Structure from Motion).

For the ASWT project, we are using SfM to document and record everything from entire sites to small excavation layers.  In other words, a digital camera and a computer take the place of the traditional pencil and sketch map technique that I became familiar with in Belize.  Creating sketch maps is somewhat fallible in terms of reliability due to human error; we can only record and note what we see or notice at the site. Often, having only a single chance to record something before we move on to the next layer. Even more often when we sketch we focus on the big things, the obvious things, not necessarily because we think the rest inconsequential, but because we cannot physically draw every detail. SfM captures all of the visual detail that we can’t see or maybe don’t even think to include at the time because we’re so focused on recording our super cool projectile point or rock alignment.

When it comes down to it, many of the steps and methods are the same (we’re still completing forms and taking notes and we aren’t taking any shortcuts), but what really changes is the end product: our results. Our notes, drawings, photos, and forms are all we have left after an excavation. SfM offers us a permanent, virtual record that preserves and offers accessibility to our excavation data for years to come (and dozens more eyes). Nothing gets skipped over, nothing forgotten.

Our Work So Far

Eagle Cave South Trench Strip numbering system.

Eagle Cave South Trench Strip numbering system. Strip 4 is where I focused my work for the first session in Eagle Cave.

As I mentioned in my introductory blog post, I am interested in archaeological applications of GIS. I also mentioned that I was intrigued by the SfM technique that I myself first learned about from this blog [Eagle Nest Canyon at the Texas Archeological Society Annual Meeting]. Now I come to you one month in, with a bit more knowledge on the project and the technique to present another perspective.

I spent the January session re-exposing a profile face, PS005, that was initially exposed in 2014. This profile sits in what we now call Strip 4, almost smack dab in the center, top section of the South Trench wall of Eagle Cave.

Digital annotation of PS005 orthophoto from 2014 before profile sampling.

Digital annotation of PS005 orthophoto from 2014 before profile sampling.

PS005 with micromorph samples superimposed and georeferenced onto the profile.

PS005 with micromorph samples superimposed and georeferenced onto the profile.

At first it was a mess. After removing the backfill and geo-cloth, we discovered that the profile face had suffered damage from continued erosion and rodent burrowing since it was originally exposed. In 2014, the investigators assigned strat numbers based on their original profile exposure –i.e. each visible stratum received a unique number.  However, they then excavated a small sampling column and did their best to follow the layer seen in profile across the unit. The presence of numerous rodent burrows, especially through the ashy layers, made strat definition challenging.

I should add one more factor, at the end of the 2014 excavations the PS005 profile was sampled by the geoarchaeologists who removed micromorphology samples.  Although done carefully, the wall was no longer pristine.

PS005 profile we exposed in 2015.

PS005 profile we exposed in 2015.

This helps explain why when we re-exposed the PS005 profile we could not easily match what we were seeing in the field to the original profile illustration. So, we decided to excavate a sampling column through a portion of the jumbled profile, using the 2014 strat numbers for our layer designations . This was done with two goals in mind:

1) Cut back eroded face (profile) and re-expose the stratigraphy.

2) Collect high-resolution samples of the matrix and artifacts within the profile.

Excavating a sampling column involves collecting the matrix of each layer (along with things like Spot Samples, Geo-matrix Samples, and samples for radiocarbon dating) that can be further analyzed in a lab.  We are not only collecting samples of each strat, but using the TDS shots of each sample and the strat location, we will add them all to the SfM model. So whoever processes and analyzes the samples can have a virtually exact geospatial reference of its origin. This will help us build an assemblage of associated artifacts, radiocarbon dates, and deposition event, aiding in our understanding of the shelter and the canyon: how it was used, when it was used, what they were doing there.

Rather than draw a standard paper and pen illustration of each layer as we excavated, we instead used SfM to document the top surface of each strat. This not only gives us an idea of what we were looking at, but it allows us to use GIS to calculate volume of matrix removed.

Field annotation of the strats in PS0010: 2015, previously PS005: 2014, that Charles and I completed.

Field annotation of the strats in PS0010: 2015, previously PS005: 2014, that Charles and I completed.

Once I finished with the sampling column, attempting to follow the strats that were assigned the previous year, the profile face that was exposed was extraordinarily rich.  In other words, by cutting back the wall we found better preserved and more complex stratigraphy. The newly exposed profile exposure is called PS010.

Previously, only about 10-12 strats were identified in this area.  We have now defined 22 individual strata from the “same” exposure. I re-photographed the profile giving us three sets of 3D data: TDS shots, 3D models of all the excavation layers, and now the model of newly exposed PS010. We now have a new high resolution 3D model to overlay all of the excavation layers and samples onto – all of which can be manipulated to aid in analysis.

Where it All Comes Together

Our field lab is where all the sets of photographs are processed. Using Photoscan we align and georeference all the images for each individual layer. The photographs, GCPs, TDS, and notes are all combined to digitally rebuild the excavation. A 3-dimensional, manipulable dataset that works hand-in-hand with all of the physical data—matrix, artifacts, etc.—and the recorded data i.e. notes, photos, etc. In order to have these georeferenced for GIS or used in photogrammetry, no less than six GCPs, ground control points, are included in each excavation exposure. Ground control points are geospatial reference points that you place on your object or in your unit, shoot in with a TDS or GPS, so that photographs and models can not only be more accurately aligned with each other, but linked to a geographic grid. This becomes incredibly handy when you are working in say, a canyon with multiple sites carrying on extensive excavations that you would like to map and relate to one another. Then, not only can you reference all of your units and sites among the canyon, but you can reference and cross-analyze your work with other sites across the region or the world. Once we have our models we can then export all or parts of the model into many different formats; GeoTIFF, TIFF, JPEG, KMZ, etc. Our models are ready to imported into GIS software where we can further manipulate and analyze them.

This shows the samples that were taken in the PS005 sampling column. They are superimposed onto the 2015: PS010 orthophoto.

This shows the samples that were taken in the PS005 sampling column. They are superimposed onto the 2015: PS010 orthophoto.

Orthophoto of complete PS010 profile face.

Orthophoto of complete PS010 profile face. An orthophoto is created once the SfM modeling is completed, GCPs added into the model, and then exported into ArcGIS for more analysis.

Our Answer

A goal of the ASWT project is to not only excavate and collect, but to gather the best data we can – or best representation of that data –backing it all up with SfM and GIS.  Structure from Motion gives us the opportunity to not only georeference our units, finds, and strata, but we can literally rebuild them, at least digitally speaking. No longer are we relying upon the traditional mapping, measuring, and sketching techniques of years past that result in rather dimensionless visualizations of excavations.

SfM also easily provides a new solution to an old problem: excavation vs. preservation. The basis of archaeology is essentially destroying material history in the name of research and discovery, so that we can preserve and record it as best we can. Granted we have gotten much, much better at recording and excavating than back in the early days of the field, there is still room for improvement and innovation. In 2014, Bryan Heisinger (2014 ASWT Intern; 2015 ASWT Staff Archaeologist) presented at the Texas Archeological Society annual meeting, on the uses of SfM and GIS for not only modeling, but extrapolating volumes of material removed and creating digital elevation models (DEMs). These can be used to study stratigraphy and depositional events of floods, people, and even animals– as Emily and Larsen can attest to. Our documentation of profiles, like PS005 and PS010 helps us build a database of all the excavations and the shelters to aid in the analysis of what is to some a rather abstract concept of time. Our work becomes more dimensional, more visible. You aren’t just looking at the profile of a wall or structure or shelter. You can virtually walk around that wall, walk into that structure, and around that shelter, without ever being there. The outreach potential is exponential.

The ASWT project personnel and many of our colleagues believe that SfM is that next step in improving archaeological documentation. Incorporating SfM and GIS technology we can model excavations with millimeter level precision recording finer detail in stratigraphy and location than ever before. Physical 3-D models that can be pieced together or pulled a part. High resolution, detailed, and accurate data that can be manipulated, viewed, and analyzed virtually any way we desire. Even better we can share our results in a brand new ways: 3D printing, virtual tours, etc., we could and can literally print pieces of art, artifacts, even a scale model of the canyon if we wanted to! This project, this technique isn’t just for the archaeologists and researchers understand the shelters better, our goal is to be able to help everyone understand the shelters better because the shelters are a part of all our histories.

To elaborate on what Charles has said numerous times and will likely say many more, “50 years ago they were using completely different techniques..50 years from now they’ll be using completely different techniques…but right now we have the technology and the opportunity to set those standards for the next 50 years. We are doing something amazing here with SfM, and sure, we’re not the only people using this method, but there could be a dang lot more of us using it.”

If you haven’t already, you should click on over to our older posts on the subject, and I highly encourage you to visit the Mark Willis Blog http://palentier.blogspot.com/, where you can see some of the other extraordinary uses of SfM 3-D modeling.

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Between a Rock and a Heart Place

By Bryan Heisinger

Last year during the 2014 Eagle Nest Canyon Expedition, the crew surveyed the land around the Shumla campus for a fresh spot to establish an experimental earth oven facility. As described by Jake Sullivan and Brooke Bonorden (see Searching for the Trifecta), earth ovens are a cooking technology used by the people of the Lower Pecos (and across the world) to bake plants and animals that would otherwise be inedible to humans.

The remains of earth ovens are found at thousands of archaeological sites across the Lower Pecos Canyonlands region, including Eagle Nest Canyon.  At Eagle Cave, the massive heep of earth oven cooking debris–mainly fire-cracked rock (FCR)–has accumulated from the repeated use of the site for constructing earth ovens, probably over thousands of years. Though highly recognizable and important to our understanding of the human occupation and use of Eagle Cave, the many hundreds of tons of burned rock that fill this and other rockshelters within Eagle Nest Canyon has been poorly studied and documented by archaeologists who have worked here over the past 80 years.

In reaction to this negligence towards FCR and earth oven research, the ASWT project has made it a priority to study and quantify the amount of earth oven cooking that occurred in the uplands and rockshelters in and around Eagle Nest Canyon.  As we documented in 2011-2012, similar evidence can be found along Dead Man’s Creek, a tributary of the Devils River, and across the region and beyond. When studying earth ovens, one of the best ways to become acquainted with the methods of earth oven technology  is to use experimental archaeology and actually build one!

The ASWT Experimental Earth Oven:

Back in 2014 when we were surveying the Shumla campus for a suitable spot to build earth ovens, we had three criteria to keep in mind while looking for the perfect location: 1. Soil, 2. Fuel,  and 3. Food. Not to mention, we took care to avoid establishing an oven at a known archaeological site! Soil, fuel, and food are the desirable location traits needed for a successful earth oven, because you need soil to dig an oven pit, you need wood to build a fire, and you need food (in our case sotol or lechuguilla) to cook. The crew eventually found a favorable spot near campus and cleared the surrounding brush for the ASWT Experimental Earth Oven locality.  Unfortunately, due to burn bans, lack of time, and conflicting personal schedules, the 2014 ENC expedition was never able to build an experimental earth oven

Fast forward to this year: On January 11th, three days after the new ASWT interns arrived at the Shumla campus, the weather conditions were highly favorable to finally build our long awaited experimental earth ovenAfter gathering enough firewood (fuel), lechuguilla and sotol (food), and close to 100 kilograms of limestone clasts from the immediate surroundings, the crew was ready to begin constructing the earth oven.

We began by digging a pit close to a meter and a half in diameter, and a half a meter in depth. The firewood (hand-gathered deadwood) was then stacked in a conical pyre (similar to a tepee), and the limestone rocks were strategically placed within the cone of firewood.

The crew agreed that it was best to light the fire the traditional Lower Pecos way, so Park Archaeologist Jack Johnson of Amistad National Recreation Area (US National Park Service) used the bloom stalk of a sotol plant to start a friction fire. In under 2 minutes, Jack had the fire blazing under the stars (for a time-lapse of the earth oven fire, watch this video by Jack Johnson: https://www.facebook.com/video.php?v=10152425529847134&pnref=story).

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The blazing conical pyre of firewood and limestone rock in shorty after it was fired.

 

After the fire burned down to embers and the rocks were glowing red hot in the bottom of the pit, the crew and several student volunteers from Texas State University began lining the the pit with prickly pear pads – the pads serve as a lower layer of packing material that helps to retain the moist heat needed to bake the food at a low temperature (ca. 100 C) for an extended period of time (typically 36 -48 hours.)

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Placing the first layer of packing material (prickly pear pads) ontop of the hot limestone rock.

 

Once the prickly pear was placed, it was time to throw in the food we collected. Lechuguilla and sotol hearts (3 each) were placed in the center of the pit on top of the prickly pear and covered again with more packing material.

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Laying the food (Sotol and lechuguilla) on top of the packing material.

 

After the remaining packing material was thrown over the food, we began to cover and cap the pit with dirt; this cap of soil insulates and holds in the steamy heat released from the rocks and suffocates the fire allowing no combustion. Now it was time to wait for our plants to bake and hope our hard labor would deliver some tasty results!

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Capping the earth oven with soil.

 

 

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Charles packing down the cap of soil to ensure no heat escapes.

 

Dinner is Served:

On the evening of January 13th, two days after we capped and sealed our earth oven, the crew returned to taste the baked desert succulents that were slow cooked over the last 48 hours. While digging the bulbs out of the pit, we noticed how the soil was still warm from the heated rocks below. The baked lechuguilla and sotol had a turned a caramelized color and had an aroma that smelled similar to a smokey artichoke.

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The baked bulbs of sotol and lechuguilla.

 

The palatability  of these baked plants sent mixed expressions across the faces of our crew, some of who enjoyed the flavor and some who didn’t.

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Tasting our baked food for the first time. The faces say it all.

 

Learning from Earth Ovens:

A great variety of scientific information potentially can be obtained from the experimental construction of earth ovens.  One aspect of earth oven use ASWT is particularly interested in is understanding the rate at which limestone rock breaks down through repeated use in earth ovens. The layer of heated limestone rocks forming the bed of an earth oven serves as a thermal storage or heating element that slowly cooks the food. During the firing process, the limestone rocks begin to break apart from the intense heat that they are exposed to (over 500 C).  Through reuse, thermal cycling–from cold to hot to cold again– causes the rocks to continue to fracture into ever smaller pieces.  Solid rocks with few flaws typically last longer than naturally fractured rocks and those with thin spots. Once the rocks becomes too small to retain heat, they are no longer effective thermal storage devices and they are discarded and tossed into what will become a debris ring around the oven pit, eventually qualifying as a burned rock midden. If we can track and measure a known mass of limestone rock (e.g., 100 kilograms/220 pounds) as it continuously breaks down into smaller rocks from heat and re-used in new earth ovens, we could then to apply this experimental rock-size attribute data to the fire-cracked rock (FCR) that we find in such profusion in the archaeological ground. In other words, this experimental use of earth ovens can potentially allow us to more accurately measure the amount of earth oven cooking that took place in Eagle Cave and other rockshelters and open sites in the region.

Eagle Cave’s Feature No. 8:

Last week, Emily and Larsen uncovered what we think is an intact earth oven heating element in their excavation unit. To a trained eye, this earth oven feature was characteristically textbook in its makeup. Many of the limestone rocks were inclined at the base of the pit and the soil that surrounded these fire-cracked rocks was heavily organic, ashy, and rich with dime-size charcoal chunks. It even appeared as if there had been a different soil that was used to cap this earth oven once long ago.

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3D model (plan view) of feature 8 in Eagle Cave. Notice the dense cluster of fire cracked rock and black/grey charcoal rich soil.

 

 

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Plan and profile view of feature 8 in Eagle Cave.

 

With intact, well-preserved finds such as Feature 8, we have the ability to obtain radiocarbon dates that can help us determine when this oven was used.  Furthermore, we can sieve the collected soil from that earth oven feature and, with the help of our collaborating archaeobotanists, identify the charred plant remains that were being processed by the people who lived in Eagle Cave. What we cannot do is accurately estimate how many times this earth oven was re-used. Was Feature 8 a one-time earth oven event? Or was it the last of series of earth ovens that had been built and re-used in this very spot using the same rocks? These are some of the questions that ASWT would like to address in our ongoing research. Through these initial tests with EEO No.1 and other experimental earth ovens to follow, we believe that the data to answer these questions could come to light.

ASWT Experimental Earth Oven (EEO) No. 1

After enjoying the success of our first experimental earth oven, we returned  a week later to dig out all the rocks from EEO No. 1.  We used 11 rocks larger than 15 cm in maximum dimension in the oven (99 kg or ~220 lbs of total), and we were able to recover all the rock that was used.  Most of the rocks survived the fire, but as you can see from the photograph below, some of the rock broke into smaller fragments.

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The rock size sorted fire cracked limestone, post earth oven firing.

Once all the rocks were pulled out of the oven, we divided the rocks into four size categories: <7.5 cm in maximum dimension, between 7.5-11 cm, 11-15 cm, and >15 cm in maximum dimension.  We used the same familiar size categories we use in the recording procedure we call “Rock Sort” which allows us to quantify the rocks from each excavation unit-layer.  The smallest two size classes (<7.5cm and 7.5-11cm) contain rocks that are too small to be effectively used again as rocks for the heating element.  After counting and weighing all the rocks in each size class, almost all of our rock (93 out of 99 kg) survived to be used again.

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Weighing the fire cracked limestone rock.

 

Likely during our next session, all the useable limestone rock from ASWT EEO No. 1 will be re-used in another experimental earth oven event.  After the second firing (ASWT EEO N0. 2.) we will once again recover all the rocks, sort the rocks into different size categories, and weight all of them.  We will continue to re-use the same rocks until the rocks all become too small (<3.5 inches) to effectively retain heat anymore. The more times we “burn” the rocks, the more data we will collect to further our goal.  We anticipate great data and results to come!