Dork Sahagian - Academia.edu (original) (raw)

Papers by Dork Sahagian

Research paper thumbnail of Toward the standardization of image analysis from X-ray tomography: Applications to vesicular rocks used for paleoelevation studies

We have developed a technique for measuring paloelevation through the study of vesicular basalts.... more We have developed a technique for measuring paloelevation through the study of vesicular basalts. It is based on determining size distributions of vesicles from x-ray tomographic data. The data requires further processing to separate partially coalesced or closely adjacent vesicles. We have found that peeling and reconstruction of voxel layers is an effective means of identifying individual entities within a complex structure from tomographic image data. In order to accomplish this, several steps are involved, some of which have traditionally required ad hoc interpretation on the part of the user. These include selection of thresholds between vesicle and rock, criteria for splitting apart partially coalesced vesicles, construction of a binning grid for resulting vesicle size classes, and interpretation of resulting histograms. With a more standardized procedure, it is possible to remove (at least partially) user input in the step by step process, thus increasing portability of the technique. The reduction of the large number of user-defined parameters in the sample analysis will make it possible to further automate the process, thus enabling faster processing and greater sample throughput. It also increases the reproducibility of results between labs or investigators analyzing similar rocks. This will be necessary for any large-scale studies of paleoelevation involving multiple labs and large numbers of sample analyses.

Research paper thumbnail of Determination of Bubble Sizes in Volcanic Melts by Confocal Microscopy and Subsequent 3D Image Analysis

Bubbles in silicic melts are studied for many characteristics including size, shape and volume to... more Bubbles in silicic melts are studied for many characteristics including size, shape and volume to understand vesiculation processes behind volcanic eruptions. This work presents a new and innovative method of reconstructing bubbles in volcanic melts using confocal microscopy. A sample of volcanic glass produced in a laboratory experiment was studied using the Laser Scanning Confocal Microscope (LSCM). LSCM have unique

Research paper thumbnail of 3D Image Analysis of Geomaterials using Confocal Microscopy

Confocal microscopy is one of the most significant advances in optical microscopy of the last cen... more Confocal microscopy is one of the most significant advances in optical microscopy of the last century. It is widely used in biological sciences but its application to geomaterials lingers due to a number of technical problems. Potentially the technique can perform non-invasive testing on a laser illuminated sample that fluoresces using a unique optical sectioning capability that rejects out-of-focus light

Research paper thumbnail of On 3D reconstruction of bubbles in volcanic ash particles

Bubbles in volcanic ash particles are primarily represented by the remnants of films and plateau ... more Bubbles in volcanic ash particles are primarily represented by the remnants of films and plateau borders from disrupting foam. Without preservation of complete bubbles, measuring bubble size distributions a challenging task, but one for which we have taken a novel approach. Concavities in ash particles retain a record of bubble sizes in the curvature of their concave surfaces that resulted

Research paper thumbnail of Horizontal and Vertical Distributions of Metals in Soils in Southeastern PA: Impact of 20th Century Zinc Smelting Operations

The region surrounding Palmerton, PA has been affected by airfall of metals from the NJ Zinc Co. ... more The region surrounding Palmerton, PA has been affected by airfall of metals from the NJ Zinc Co. smelter along the Lehigh River just north of the Kittatinny Ridge. The deposition of zinc, cadmium, lead, and arsenic, led to the destruction of a forest ecosystem in the immediate vicinity and metals contamination in the town and surrounding area. Although the smelter

Research paper thumbnail of Earth System Atlas: citable publication and visualization of datasets

The rapid growth of digital data archived around the world, stored on a large number of different... more The rapid growth of digital data archived around the world, stored on a large number of different web servers and in numerous formats, are often under-exploited because of the difficulties that arise from data persistence, ease of access and format incompatibilities. The metadata and physical infrastructure necessary to make these data widely accessible and useful to the scientific community and the wider general audience (policy makers, educators, and the lay public) is often incomplete, or missing altogether. Web access to data also has a tendency to disappear when funds are no longer available to support these scattered individual efforts. As a result, access to and knowledge of data sources and their reliability and limitations is frequently a major stumbling block for scientists, policy makers, NGOs, educators and others. Data from significantly different disciplines have been stored and manipulated in highly different ways, and while it is possible to overlay diverse data on a...

Research paper thumbnail of 3D Volumetric Analysis of Fluid Inclusions Using Confocal Microscopy

Fluid inclusions preserve valuable information regarding hydrothermal, metamorphic, and magmatic ... more Fluid inclusions preserve valuable information regarding hydrothermal, metamorphic, and magmatic processes. The molar quantities of liquid and gaseous components in the inclusions can be estimated from their volumetric measurements at room temperatures combined with knowledge of the PVTX properties of the fluid and homogenization temperatures. Thus, accurate measurements of inclusion volumes and their two phase components are critical. One of

Research paper thumbnail of Bubbledrive-1: A numerical model of volcanic eruption mechanisms driven by disequilibrium magma degassing

Journal of Volcanology and Geothermal Research, 2005

We have developed a numerical model for magma dynamics in volcanic conduits that involves conduit... more We have developed a numerical model for magma dynamics in volcanic conduits that involves conduit flow driven by a detailed treatment of bubble growth. The “Bubbledrive-1” model can be characterized by several unique aspects, including treatment of the transient problem, specific eruption triggers, disequilibrium degassing, a full-scale bubble growth module, and steady-state eruption in the case of constant recharge from

Research paper thumbnail of Assessing the Practicality and Viability of Basalt Vesicle Paleoaltimetry in Solving Regional Tectonic Problems in the Basin and Range

Understanding the paleoelevation history of orogens is fundamental to answering a number of signi... more Understanding the paleoelevation history of orogens is fundamental to answering a number of significant questions about continental deformation. Most paleoaltimeters rely on proxies for measuring paleoelevation that may be affected by factors other than elevation, such as climate. The basalt vesicle paleoaltimeter avoids problems associated with such proxies by directly measuring the paleo-atmospheric pressure recorded by vesicle size-distributions in basalt

Research paper thumbnail of Bubble size distributions across some basaltic lava flows with simple vesiculation

Research paper thumbnail of Airfall of metals from the Palmerton, PA, zinc plant: Distribution and preservation

The stacks of the NJ Zinc Co. created airfall deposits throughout the 20th century in the region ... more The stacks of the NJ Zinc Co. created airfall deposits throughout the 20th century in the region surrounding Palmerton, PA. The deposition of zinc, cadmium, lead, and arsenic, led to the destruction of a forest ecosystem along the neighboring Kittatinny Ridge and metals contamination in the town and surrounding area. Although the smelter was closed in the 1980's, concerns linger

Research paper thumbnail of Sequence stratigraphy and sea-level history of Oligocene strata of the northern Aral Sea region (Kazakhstan): Implications for glacioeustatic reconstructions

Geological Society of America Bulletin, 1999

... Mikhail A. Akhmetiev Institute of Geology, Russian Academy of Sciences, Moscow, Russia 109017... more ... Mikhail A. Akhmetiev Institute of Geology, Russian Academy of Sciences, Moscow, Russia 109017 ... For example, the Aral Formation contains nu-merous bones of fresh-water fish, remnants of marine fauna such as shark teeth, clupeids (her-rings), and delphinid bones (Lucas et ...

Research paper thumbnail of Global and regional sea-level changes and the hydrological cycle

Global and Planetary Change, 2001

Editorial Global and regional sea-level changes and the hydrological cycle 0921-8181/02/$ -see fr... more Editorial Global and regional sea-level changes and the hydrological cycle 0921-8181/02/$ -see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 -8 1 8 1 ( 0 1 ) 0 0 1 4 4 -8 www.elsevier.com/locate/gloplacha Global and Planetary Changes 32 (2002) vi -viii

Research paper thumbnail of 3D particle size distributions from 2D observations: stereology for natural applications

Journal of Volcanology and Geothermal Research, 1998

We have developed a general formulation for stereological analysis of particle distributions whic... more We have developed a general formulation for stereological analysis of particle distributions which is applicable to any particle size or size distribution (not limited to log-normal, unimodal, etc.). We have applied numerical techniques to define intersection probability distributions for any shapes (previously only known for spheres), and quantified the errors involved in using spherical coefficients for various non-spherical particles. This

Research paper thumbnail of Bubbles in volcanic systems

Research paper thumbnail of Carbon cycle dynamics in the geologic record: Speleothems as a source for new biogeochemical and paleoclimate information

Many of the key outstanding questions in paleoclimate and biogeochemical cycles involve terrestri... more Many of the key outstanding questions in paleoclimate and biogeochemical cycles involve terrestrial ecosystems. Caves provide an important depositional environment for sedimentary archives of past and present terrestrial environmental changes. Until recently, the tools available to the research community have been appropriate for coarse resolution studies, but have been inadequate to address other important questions such as: 1. How have

Research paper thumbnail of Modelling

Atmospheric Chemistry in a Changing World, 2003

Research paper thumbnail of Recommendations provide direction for sea-level rise research

Eos, Transactions American Geophysical Union, 2000

Research paper thumbnail of 3D reconstruction of volcanic ash particles using Stereo-SEM: two study cases from 200 Ky ash-rich eruptions

Volcanic eruptions are often characterized by contrasting degrees of fragmentation during a singl... more Volcanic eruptions are often characterized by contrasting degrees of fragmentation during a single eruptive event, suggesting different decompression histories. The morphology of the ash fragments, products of many ash-rich eruptions, retains a record of bubble size at the time of fragmentation in the curvature of the convex surfaces on the ash fragments. The quantitative description of bubble distribution is a

Research paper thumbnail of Modelling

The chemistry of the atmosphere is controlled by a large number of complex chemical and physical ... more The chemistry of the atmosphere is controlled by a large number of complex chemical and physical processes. The study of such a complex system requires the use of numerical models, which have improved substantially over the past ten years. These models are mathematical representations of the main physical and chemical processes controlling the spatial and temporal distributions of trace gases

Research paper thumbnail of Toward the standardization of image analysis from X-ray tomography: Applications to vesicular rocks used for paleoelevation studies

We have developed a technique for measuring paloelevation through the study of vesicular basalts.... more We have developed a technique for measuring paloelevation through the study of vesicular basalts. It is based on determining size distributions of vesicles from x-ray tomographic data. The data requires further processing to separate partially coalesced or closely adjacent vesicles. We have found that peeling and reconstruction of voxel layers is an effective means of identifying individual entities within a complex structure from tomographic image data. In order to accomplish this, several steps are involved, some of which have traditionally required ad hoc interpretation on the part of the user. These include selection of thresholds between vesicle and rock, criteria for splitting apart partially coalesced vesicles, construction of a binning grid for resulting vesicle size classes, and interpretation of resulting histograms. With a more standardized procedure, it is possible to remove (at least partially) user input in the step by step process, thus increasing portability of the technique. The reduction of the large number of user-defined parameters in the sample analysis will make it possible to further automate the process, thus enabling faster processing and greater sample throughput. It also increases the reproducibility of results between labs or investigators analyzing similar rocks. This will be necessary for any large-scale studies of paleoelevation involving multiple labs and large numbers of sample analyses.

Research paper thumbnail of Determination of Bubble Sizes in Volcanic Melts by Confocal Microscopy and Subsequent 3D Image Analysis

Bubbles in silicic melts are studied for many characteristics including size, shape and volume to... more Bubbles in silicic melts are studied for many characteristics including size, shape and volume to understand vesiculation processes behind volcanic eruptions. This work presents a new and innovative method of reconstructing bubbles in volcanic melts using confocal microscopy. A sample of volcanic glass produced in a laboratory experiment was studied using the Laser Scanning Confocal Microscope (LSCM). LSCM have unique

Research paper thumbnail of 3D Image Analysis of Geomaterials using Confocal Microscopy

Confocal microscopy is one of the most significant advances in optical microscopy of the last cen... more Confocal microscopy is one of the most significant advances in optical microscopy of the last century. It is widely used in biological sciences but its application to geomaterials lingers due to a number of technical problems. Potentially the technique can perform non-invasive testing on a laser illuminated sample that fluoresces using a unique optical sectioning capability that rejects out-of-focus light

Research paper thumbnail of On 3D reconstruction of bubbles in volcanic ash particles

Bubbles in volcanic ash particles are primarily represented by the remnants of films and plateau ... more Bubbles in volcanic ash particles are primarily represented by the remnants of films and plateau borders from disrupting foam. Without preservation of complete bubbles, measuring bubble size distributions a challenging task, but one for which we have taken a novel approach. Concavities in ash particles retain a record of bubble sizes in the curvature of their concave surfaces that resulted

Research paper thumbnail of Horizontal and Vertical Distributions of Metals in Soils in Southeastern PA: Impact of 20th Century Zinc Smelting Operations

The region surrounding Palmerton, PA has been affected by airfall of metals from the NJ Zinc Co. ... more The region surrounding Palmerton, PA has been affected by airfall of metals from the NJ Zinc Co. smelter along the Lehigh River just north of the Kittatinny Ridge. The deposition of zinc, cadmium, lead, and arsenic, led to the destruction of a forest ecosystem in the immediate vicinity and metals contamination in the town and surrounding area. Although the smelter

Research paper thumbnail of Earth System Atlas: citable publication and visualization of datasets

The rapid growth of digital data archived around the world, stored on a large number of different... more The rapid growth of digital data archived around the world, stored on a large number of different web servers and in numerous formats, are often under-exploited because of the difficulties that arise from data persistence, ease of access and format incompatibilities. The metadata and physical infrastructure necessary to make these data widely accessible and useful to the scientific community and the wider general audience (policy makers, educators, and the lay public) is often incomplete, or missing altogether. Web access to data also has a tendency to disappear when funds are no longer available to support these scattered individual efforts. As a result, access to and knowledge of data sources and their reliability and limitations is frequently a major stumbling block for scientists, policy makers, NGOs, educators and others. Data from significantly different disciplines have been stored and manipulated in highly different ways, and while it is possible to overlay diverse data on a...

Research paper thumbnail of 3D Volumetric Analysis of Fluid Inclusions Using Confocal Microscopy

Fluid inclusions preserve valuable information regarding hydrothermal, metamorphic, and magmatic ... more Fluid inclusions preserve valuable information regarding hydrothermal, metamorphic, and magmatic processes. The molar quantities of liquid and gaseous components in the inclusions can be estimated from their volumetric measurements at room temperatures combined with knowledge of the PVTX properties of the fluid and homogenization temperatures. Thus, accurate measurements of inclusion volumes and their two phase components are critical. One of

Research paper thumbnail of Bubbledrive-1: A numerical model of volcanic eruption mechanisms driven by disequilibrium magma degassing

Journal of Volcanology and Geothermal Research, 2005

We have developed a numerical model for magma dynamics in volcanic conduits that involves conduit... more We have developed a numerical model for magma dynamics in volcanic conduits that involves conduit flow driven by a detailed treatment of bubble growth. The “Bubbledrive-1” model can be characterized by several unique aspects, including treatment of the transient problem, specific eruption triggers, disequilibrium degassing, a full-scale bubble growth module, and steady-state eruption in the case of constant recharge from

Research paper thumbnail of Assessing the Practicality and Viability of Basalt Vesicle Paleoaltimetry in Solving Regional Tectonic Problems in the Basin and Range

Understanding the paleoelevation history of orogens is fundamental to answering a number of signi... more Understanding the paleoelevation history of orogens is fundamental to answering a number of significant questions about continental deformation. Most paleoaltimeters rely on proxies for measuring paleoelevation that may be affected by factors other than elevation, such as climate. The basalt vesicle paleoaltimeter avoids problems associated with such proxies by directly measuring the paleo-atmospheric pressure recorded by vesicle size-distributions in basalt

Research paper thumbnail of Bubble size distributions across some basaltic lava flows with simple vesiculation

Research paper thumbnail of Airfall of metals from the Palmerton, PA, zinc plant: Distribution and preservation

The stacks of the NJ Zinc Co. created airfall deposits throughout the 20th century in the region ... more The stacks of the NJ Zinc Co. created airfall deposits throughout the 20th century in the region surrounding Palmerton, PA. The deposition of zinc, cadmium, lead, and arsenic, led to the destruction of a forest ecosystem along the neighboring Kittatinny Ridge and metals contamination in the town and surrounding area. Although the smelter was closed in the 1980's, concerns linger

Research paper thumbnail of Sequence stratigraphy and sea-level history of Oligocene strata of the northern Aral Sea region (Kazakhstan): Implications for glacioeustatic reconstructions

Geological Society of America Bulletin, 1999

... Mikhail A. Akhmetiev Institute of Geology, Russian Academy of Sciences, Moscow, Russia 109017... more ... Mikhail A. Akhmetiev Institute of Geology, Russian Academy of Sciences, Moscow, Russia 109017 ... For example, the Aral Formation contains nu-merous bones of fresh-water fish, remnants of marine fauna such as shark teeth, clupeids (her-rings), and delphinid bones (Lucas et ...

Research paper thumbnail of Global and regional sea-level changes and the hydrological cycle

Global and Planetary Change, 2001

Editorial Global and regional sea-level changes and the hydrological cycle 0921-8181/02/$ -see fr... more Editorial Global and regional sea-level changes and the hydrological cycle 0921-8181/02/$ -see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 -8 1 8 1 ( 0 1 ) 0 0 1 4 4 -8 www.elsevier.com/locate/gloplacha Global and Planetary Changes 32 (2002) vi -viii

Research paper thumbnail of 3D particle size distributions from 2D observations: stereology for natural applications

Journal of Volcanology and Geothermal Research, 1998

We have developed a general formulation for stereological analysis of particle distributions whic... more We have developed a general formulation for stereological analysis of particle distributions which is applicable to any particle size or size distribution (not limited to log-normal, unimodal, etc.). We have applied numerical techniques to define intersection probability distributions for any shapes (previously only known for spheres), and quantified the errors involved in using spherical coefficients for various non-spherical particles. This

Research paper thumbnail of Bubbles in volcanic systems

Research paper thumbnail of Carbon cycle dynamics in the geologic record: Speleothems as a source for new biogeochemical and paleoclimate information

Many of the key outstanding questions in paleoclimate and biogeochemical cycles involve terrestri... more Many of the key outstanding questions in paleoclimate and biogeochemical cycles involve terrestrial ecosystems. Caves provide an important depositional environment for sedimentary archives of past and present terrestrial environmental changes. Until recently, the tools available to the research community have been appropriate for coarse resolution studies, but have been inadequate to address other important questions such as: 1. How have

Research paper thumbnail of Modelling

Atmospheric Chemistry in a Changing World, 2003

Research paper thumbnail of Recommendations provide direction for sea-level rise research

Eos, Transactions American Geophysical Union, 2000

Research paper thumbnail of 3D reconstruction of volcanic ash particles using Stereo-SEM: two study cases from 200 Ky ash-rich eruptions

Volcanic eruptions are often characterized by contrasting degrees of fragmentation during a singl... more Volcanic eruptions are often characterized by contrasting degrees of fragmentation during a single eruptive event, suggesting different decompression histories. The morphology of the ash fragments, products of many ash-rich eruptions, retains a record of bubble size at the time of fragmentation in the curvature of the convex surfaces on the ash fragments. The quantitative description of bubble distribution is a

Research paper thumbnail of Modelling

The chemistry of the atmosphere is controlled by a large number of complex chemical and physical ... more The chemistry of the atmosphere is controlled by a large number of complex chemical and physical processes. The study of such a complex system requires the use of numerical models, which have improved substantially over the past ten years. These models are mathematical representations of the main physical and chemical processes controlling the spatial and temporal distributions of trace gases