Obsidian Hydration Research Articles

Environmental Degradation and the Classic Maya Collapse at Copan, Honduras (a.d. 600–1250): Evidence From Studies of Household Survival

AbstractThe Late Classic Maya abandonment of the Copan Valley, Honduras, began in the ninth centurya.d. and lasted approximately 250–300 years. The relationship between local ecological setting and residential group abandonment is examined by applying event-history analysis to the known occupation spans of 140 residential mound groups, dated by obsidian hydration. Late Classic households in ecologically vulnerable sections of the Copan Valley—as measured by slope, soil type, and natural vegetation—had significantly higher risk of abandonment than households in more ecologically stable settings. Abandonment risk rises sharply in all regions at the end of the seventh centurya.d. Both computerized agricultural simulations and settlement demographic reconstructions indicate that increased levels of agricultural intensification necessary to meet the subsistence needs of Copan's growing population would have led to large-scale erosion in upland areas and a significant reduction of soil fertility in all regions of the valley at that time. Mound-group abandonment patterns tend to support the hypothesis that environmental degradation played a dominant role in the collapse of the Copan polity.

The Postclassic Occupation at Otumba

AbstractThe Aztec city-state of Otumba is the focus of a long-term project of archaeological investigation. Analysis of surface and excavated ceramics and obsidian-hydration dates for the capital—Otumba—indicate a dispersed Mazapan occupation, a scattered early Aztec (Aztec II) occupation, and an intense Late Aztec (Aztec III) and Early Colonial (Aztec III/IV) occupation. In the paper we incorporate recent radiocarbon dates to refine the local late Postclassic chronology. A cluster of hydration dates suggests the early (Mazapan) occupation starts ca. a.d. 900. Aztec II ceramics, which are widely distributed in surface artifact collections, may begin as early as a.d. 1200 and continue until a.d. 1400, overlapping Aztec III ceramics, which we have dated from a.d. 1350 ± 50 to 1521 and later. Otumba continued to have a substantial occupation until ca. a.d. 1600/1620 in the early seventeenth century, when most of the Aztec town was abandoned.

Is Obsidian Hydration Dating Affected by Relative Humidity?

Experiments carried out under temperatures and relative humidities that approximate ambient conditions show that the rate of hydration of obsidian is a function of the relative humidity, as well as of previously established variables of temperature and obsidian chemical composition. Measurements of the relative humidity of soil at 25 sites and at depths of between 0.01 and 2 m below ground show that in most soil environments, at depths below about 0.25 m, the relative humidity is constant at 100%. We have found that the thickness of the hydrated layer developed on obsidian outcrops exposed to the sun and to relative humidities of 30-90% is similar to that formed on other portions of the outcrop that were shielded from the sun and exposed to a relative humidity of approximately 100%. Surface samples of obsidian exposed to solar heating should hydrate more rapidly than samples buried in the ground. However, the effect of the lower mean relative humidity experiences by surface samples tends to compensate for the elevated temperature, which may explain why obsidian hydration ages of surface samples usually approximate those derived from buried samples.

Obsidian hydration dating of a Pleistocene age site from the Manus Islands, Papua New Guinea

Obsidian hydration dating relies on the precise measurement of the depth of hydration developed over time in the surface of obsidians, but the loss of surface by natural dissolution at some archaeological sites can result in erroneous age determinations. By focussing the hydration measurement on internal crack surfaces protected from external surface erosion, acceptable results have been achieved from a Pleistocene age site in Papua New Guinea. Measurement of the hydration profile in thin sections of the sampled obsidian by computer imaging results in an improved reading error for the hydration depth. By using the system on archaeological obsidians from the Pamwak site, the relative age results are more consistent with the radiocarbon age determinations than conventional obsidian hydration dating.

The Obsidian Hydration Dating Project at Copan: A Regional Approach and Why It Works

Settlement research at Copán, Honduras, since 1984 has produced the largest set of obsidian-hydration dates from excavated contexts available for Mesoamerica (Webster and Freter 1990). Geoffrey Braswell (1992) has criticized the methodology underlying our research, specific associations of our published data, and particularly our reconstruction of a demographic and political decline at Copán that extended well beyond A.D. 900. Braswell has incorrectly characterized the Copan Obsidian Hydration Dating Project’s methodology, and makes many factual errors in assessing the Copán data. In this paper the authors correct these errors, discuss basic issues of obsidian-hydration-dating methodology, and offer new data from Copán to evaluate the efficacy of hydration dating as a method and its potential future application for Mesoamerica as a whole.

Homogeneity of water content in obsidian from the coso volcanic field: Implications for obsidian hydration dating

AbstractUsers of the obsidian hydration dating method have routinely assumed that artifacts which originate from the same geological flow will be of the same chemical composition and thus hydrate at the same rate under equivalent conditions of temperature and relative humidity. Recent laboratory experimentation into the hydration process has shown that the intrinsic water content of the glass is the dominant factor in establishing the rate of hydration. Water content determinations on a large suite of samples from numerous prehistoric quarries within the Coso volcanic field, California, indicated that water content values, and thus hydration rate, varied significantly on a within flow basis. It is recommended that water determinations be made on individual artifacts prior to obsidian hydration dating. © 1993 John Wiley & Sons, Inc.

Obsidian-Hydration Dating: Its Past, Present, and Future Application in Mesoamerica

AbstractThe reconstruction of time is a central concern all archaeologists must address in their research; few, however, are fully aware of the potential of all the dating methods at their disposal. For this reason, this paper summarizes the developmental history and current level of field application of obsidian-hydration dating. It (1) reviews how this dating technique was first discovered and applied, (2) details our current knowledge of the process of hydration and which variables affect its rate, (3) discusses the relative advantages and limitations of the three primary approaches employed to construct hydration chronologies, and (4) presents a protocol for its future application in Mesoamerica. The synthesis of this body of hydration-dating research may help archaeologists more constructively decide how and when to apply this unique and versatile dating technique to their specific research questions by providing the information and guidelines necessary for recovering pertinent field data.

Obsidian-hydration dating of fluvially reworked sediments in the West Yellowstone region, Montana

This study evaluates obsidian-hydration dating in postglacial fluvial terraces cut into an outwash plain near West Yellowstone, Montana. Fluvial transport fractures obsidian grains. However, some old hydration rinds may be preserved, thus, a grain may record several fracturing events. The most recent fracturing event at West Yellowstone is recorded in surface sediments from all of the terraces, which were cut in a shorter period of time than the technique can discern. They formed about 19,000 ± 1000 yr ago, using published hydration-rate estimates and a mean rind thickness of 6.34 ± 0.14 μm (1 SE). Alternatively, the application of published hydration-rate constants for the Obsidian Cliff flow with an estimated effective hydration temperature of 1.4°C yield an age of 24,400 ± 1100 yr (1 SE). Thicker rinds record fracturing during Bull Lake glaciation and cooling cracks from the emplacement of several source flows. Much of the observed spread in rind thicknesses (6.34 ± 1.69 μm: 1 SD) is probably the result of chemically induced variations in hydration rate. Terrace ages based on a single rind would range from 13,000 to 39,000 yr (±1 SD). Therefore, it is inappropriate to (1) use a set of hydration-rate constants determined from a single sample to calculate ages for multiple artifacts or geological samples, (2) date an archaeological or geological event on the basis of a single artifact, or (3) generate a chronostratigraphy on the basis of individual dates as a function of depth. Multiple evaluations of source chemistry and hydration rates and multiple rind measurements are required to date fracturing events.

Obsidian-Hydration Dating, the Coner Phase, and Revisionist Chronology at Copan, Honduras

The technique of obsidian-hydration dating contains great potentials for error, from both laboratory determinations of rate constants and measurements of effective hydration temperatures (EHTs) in the field. The rate constants used to determine these dates are of questionable validity and need to be independently verified. Significantly, no measurements of EHTs were taken at the site of Copán, Honduras, until the majority of the obsidianhydration dates were calculated. An error of but a few Kelvins in estimated EHT can lead to dates that are in error by several centuries. In view of the likelihood of large errors in the Copán obsidian dates, the assertion that the Late Classic Coner phase should be extended beyond A. D. 900 (Webster and Freter 1990a) is premature.

The Martis Complex Revisited

In 1953 a prehistoric culture was first identified in the western Great Basin and the north-central Sierra Nevada and termed the “Martis Complex.” Since questions have been raised about the characterization of this Complex, this article is a review of research and adds new field data since its original description. Of nine traits originally proposed to identify the Martis Complex, two had been questioned at that time; they remain as questionable traits. The other seven have been reinforced by more recent data, and three new diagnostic traits are proposed on the basis of new information on the Complex. Recent dating by carbon-14 and obsidian hydration measurements affirm the existence of the Martis Complex between 2000 B.C. and 500 A.D.

Obsidian hydration dating and temperature controls in the Punta Negra region of Northern Chile

Effective hydration temperature (EHT) is essential for the computation of obsidian hydration dates. In the Atacama Desert, the scarcity of air-temperature records combines with extremes of elevation and local temperature to encourage, or even require, the use of buried thermal cells to record on-site mean annual temperatures. Compositional analysis (sourcing) and hydration rate development in the laboratory are also necessary, especially where other dating methods are unavailable to confirm the hydration rate. Paleoindian or Early Archaic through modern obsidian dates support a human settlement pattern history derived from archaeological/geomorphological studies of climatological and hydrological change.

A Simulation of Copan Populatin History and its Implications

AbstractSeveral projects carried out at Copan since 1975 provide extensive settlement data that form the basis for a simulation of Copan population history between A.D. 400–1250. Most important is a set of 2,048 obsidian hydration dates, associated with 15% of all known sites, that allows unprecedented chronological control of occupational episodes at domestic sites of all social ranks. This article summarizes the results of our simulation, and some of its implications for agricultural intensification, sociopolitical structure, and labor demand for elite construction projects.

Chronological Research at Copan:Methods and implications

AbstractAs a consequence of long-term archaeological research at Copan, 1,425 archaeological sites containing 4,507 structures have been located and mapped over an area of 135 km2. As part of the PAC II research, 200 archaeological sites representing a 15% stratified random sample of all valley sites were test excavated from 1983–1989. From these excavations, 2,150 obsidian hydration dates were processed, representing the largest number of chronometric dates from controlled contexts currently available from any southern Lowland Maya site. Based on this chronological research, there appears to be an excellent fit with various other available chronological techniques for all time phases except the ending date of the important Coner ceramic phase, which now appears to have extended to A.D. 1250. This more detailed Copan chronology suggests that the political collapse of the Main Group and immediate vicinity was quite sudden, taking place c. A.D. 800–830. Beyond that, however, the chronometric data provide evidence that some of the secondary elite, or lineage heads, and large numbers of rural commoners continued to reside within the valley in reduced courtyard groups or small rural hamlets for about 400 years following the decentralization of the Copan polity.

The Experimental Hydration of Obsidian as a Function of Relative Humidity and Temperature

The experimental hydration of obsidian for up to 30 days is described at relative humidities (RH) of 60, 90, 95, and 100 percent and at temperatures of 150, 160, and 175°C. Under isothermal conditions, the rate of hydration increased by as much as 25 percent between 60 and 100 percent RH. The RH dependence is nonlinear, with the majority of the rate increase occurring between 90 and 100 percent RH. The effect of RH can be related to the driving force for molecular water diffusion in obsidians as described by the chemical potential difference between water sorbed onto the obsidian surface and intrinsic water in the obsidian. The differences in hydration rates caused by RH differences in experiments approximate the error commonly described for obsidian-hydration dating. These results suggest that obsidian-hydration dating requires a knowledge of the site temperature and relative humidity in order to accurately generate age estimates.

Structure and Change in a Late Classic Maya Domestic Group at Copan, Honduras

The dynamic process involving the establishment, growth, and decline of Patio Group 9M-22-A, an elite Late Classic Maya domestic group at Copan, Honduras, is described in terms of 11 time spans. Architectural and stratigraphie changes occurring within these time spans are integrated with 70 obsidian hydration dates and demonstrate that the patio group was occupied to the end of the tenth century, with sporadic activity continuing into the eleventh century. Changes in the leadership roles spanning several generations within the patio group are inferred from the archaeological data and related to socioeconomic variables influencing the development cycle.

Obsidian Hydration Dating: The Effects of Mean Exponential Ground Temperature and Depth of Artifact Recovery

The results of a study of obsidian hydration dating conducted in northern New Mexico demonstrate that for a high degree of temporal resolution, both precise depth provenience for artifacts and measurement of the mean exponential ground temperature at several depths in the site may be required. When dates for artifacts recovered from one site were calculated using thermal cell temperatures from a site that was 24 m higher in elevation and located only 1km away, the difference was on the order of 250–300 years. The difference between dates calculated using an effective hydration temperature estimated from air temperature data and the known dates for the sites was as large as 100 years in some cases.This study shows that the effect of using a precise depth of recovery in date calculations appears to decrease with depth and to be strongest in the first meter below the present ground surface. Effective hydration temperatures at one site varied by more than 3°C in the first meter. A change 1°C in the effective hydration temperature may have a significant effect on an obsidian hydration date.

Obsidian Hydration Dating: The Effects of Mean Exponential Ground Temperature and Depth of Artifact Recovery

Obsidian Hydration Dating: The Effects of Mean Exponential Ground Temperature and Depth of Artifact Recovery

Hopewell Obsidian Studies: Behavioral Implications of Recent Sourcing and Dating Research

Specific questions regarding the antiquity of major midwestern Hopewell culture sites and their role in regional exchange systems are addressed in this paper through the dating (obsidian hydration) and compositional characterization (neutron activation analysis [NAA] and atomic absorption spectroscopy [AAS]) of obsidian artifacts. The analysis of 34 specimens from the Seip, Mound City, and Hopewell sites, Ohio, and the Naples site, Illinois, increases fivefold the number of chronometric dates available from these sites and expands the sample of compositionally identified specimens beyond those resulting from Griffin et al."s (1969) pioneering work. The resulting hydration dates support earlier estimates of the age of these contexts based on 14C or artifact seriation alone. The range of dates (78 B.C.-A.D. 347) and the compositional variety within the sample favors an expanded view of the nature of obsidian trade in the Midwest to include additional western sources, a longer episode of importation, and possible changes in the sources used through time.

Hopewell Obsidian Studies: Behavioral Implications of Recent Sourcing and Dating Research

Specific questions regarding the antiquity of major midwestern Hopewell culture sites and their role in regional exchange systems are addressed in this paper through the dating (obsidian hydration) and compositional characterization (neutron activation analysis [NAA] and atomic absorption spectroscopy [AAS]) of obsidian artifacts. The analysis of 34 specimens from the Seip, Mound City, and Hopewell sites, Ohio, and the Naples site, Illinois, increases fivefold the number of chronometric dates available from these sites and expands the sample of compositionally identified specimens beyond those resulting from Griffin et al."s (1969) pioneering work. The resulting hydration dates support earlier estimates of the age of these contexts based on 14C or artifact seriation alone. The range of dates (78 B.C.-A.D. 347) and the compositional variety within the sample favors an expanded view of the nature of obsidian trade in the Midwest to include additional western sources, a longer episode of importation, and possible changes in the sources used through time.

Settlement History and the Classic Collapse at Copan: A Redefined Chronological Perspective

Surveys, test pitting, and large-scale excavation carried out since 1975 around the Classic Maya center of Copan, in western Honduras, have yielded a wealth of settlement data. A total of 2,048 obsidian-hydration dates have redefined the Late Classic Coner ceramic phase, showing it to extend well into the Early Postclassic. Sites with Coner ceramics exhibit much more intraphase chronological variation than expected. The Classic “collapse” at Copan was much more protracted than thought previously. There is an abrupt royal collapse at about A.D. 800, but subroyal elite activity continues for another 200 years, and population declines gradually over a period of four centuries.