Carlson, William D.

Prusevich, Alexander A.

Sahagian, Dork L.

English

UNH Scholars' Repository

University of New HampshireUniversity of New Hampshire Scholars' RepositoryFaculty Publications7-1-2003Analysis of Vesicular Basalts and LavaEmplacement Processes for Application as aPaleobarometer/Paleoaltimeter: A ReplyDork L. SahagianLehigh UniversityAlexander A. PrusevichUniversity of New Hampshire, Durham, alex.proussevitch@unh.eduWilliam D. CarlsonUniversity of Texas at AustinFollow this and additional works at: https://scholars.unh.edu/faculty_pubsThis Article is brought to you for free and open access by University of New Hampshire Scholars' Repository. It has been accepted for inclusion inFaculty Publications by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contactnicole.hentz@unh.edu.Recommended CitationSahagian, D., Proussevitch, A., & Carlson, W. (2003). Analysis of Vesicular Basalts and Lava Emplacement Processes for Application asa Paleobarometer/Paleoaltimeter: A Reply. The Journal of Geology, 111(4), 502-504. doi:10.1086/375278[The Journal of Geology, 2003, volume 111, p. 502–504]  2003 by The University of Chicago. All rights reserved. 0022-1376/2003/11104-0009$15.00502Analysis of Vesicular Basalts and Lava Emplacement Processes forApplication as a Paleobarometer/Paleoaltimeter: A ReplyD. Sahagian, A. Proussevitch,1 and W. Carlson2Climate Change Research Center, Institute for the Study of Earth, Oceans, and Space, and Department of EarthSciences, University of New Hampshire, Durham, New Hampshire 03824, U.S.A.(e-mail: dork.sahagian@uhn.edu)The use of vesicular basalts as a tool for the mea-surement of paleoelevation is based on the calcu-lation of atmospheric pressure from the differencebetween vesicle sizes in the tops and bottoms offlows. Assuming that the bubbles were a well-mixed population at eruption from the vent, thedifference in size is caused by the pressure of thelava overburden relative to external atmosphericpressure. Thus, if the flow thickness and densityare known or measured and the size distributionscan be determined, atmospheric pressure and thuselevation can be calculated. In this analysis, thetwo most difficult (and thus critical) measurementsare the vesicle sizes and flow thickness. A methodto measure the former has been developed (Ketch-am and Carlson 2001; Proussevitch and Sahagian2001) so that the remaining practical limitation onusing the technique of Sahagian et al. (2002a,2002b) is the ability of the field geologist to deter-mine that the measured flow thickness representsthe thickness of the flow at the time that the upperand lower 10 cm or so (from which samples wouldbe taken) solidified to “lock in” the vesicle sizes.The primary concern regarding thickness is thatthere may have been deflation or inflation of theflow after the top and bottom solidified (Bondre2003). While it may be optimal to identify a thinlobe or breakout where late-stage inflation wouldnot be expected, as suggested by Bondre (2003), thisis not always possible because of incomplete fieldexposures, especially for older flows. Consequently,flows must be examined critically in the field incross section. For the study of Sahagian et al.(2002a) in Hawaii, we did not sample strictly fromManuscript received January 18, 2003.1 Department of Earth Sciences, University of New Hamp-shire, Durham, New Hampshire 03824, U.S.A.2 Department of Geological Sciences, University of Texas,Austin, Texas 78712, U.S.A.thin lobes or breakouts but rather from all parts ofthe flows—near the vent, on the flank of the vol-cano, and around Hilo. The criteria for establishingsimple emplacement were unrelated to lateral ge-ometry but rather were based on vesicle populationstructure in vertical cross section. The character-istic features of simple emplacement can be rec-ognized in flows of any age or exposure quality,provided there is a complete cross section throughthe flow.The question becomes how to identify simpleemplacement in the field. In flow cross sections,there are often confounding features—such as mul-tiple vesicular zones, discontinuities in the vesic-ularity profile, very large vesicles, pipes, evidenceof shear deformation, and “xenoliths” of previouslysolidified lava—that should represent a red flag tothe field geologist and make it easy to disqualifyflows with such complexities. The absence of suchobvious features is not necessarily a guarantee thatthe flow experienced simple emplacement, so thevesicularity profile, thickness of upper vesicularzone relative to flow thickness, and size distribu-tion profiles must be critically examined relativeto the profile expected for simple emplacement.Inflation, even if continuous rather than pulsed,would disrupt the rise and coalescence of bubblesthat result in the appropriate bimodal or trimodalsize distribution in the upper vesicular zone and isidentifiable on that basis. If inflation occurs rela-tively early in the emplacement process, before so-lidification of the upper and lower 10 cm or so ofthe flow (and before significant bubble rise and co-alescence), the vesicle sizes will adjust to accom-modate the “new” thickness, in which case theanalysis would apply to the inflated thickness ofthe flow, and paleoelevation studies could beconducted with the thickness measured in thefield. Also, once there is a thick upper crust thatmakes it possible to generate internal lava pres-This content downloaded from 132.177.229.130 on November 09, 2018 06:32:03 AMAll use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).Journal of Geology D I S C U S S I O N A N D R E P L Y 503sures greater than hydrostatic (Hon et al. 1994), itno longer matters what the internal pressure is be-cause the upper (and lower) vesicles have been fro-zen in already. However, it is not clear how to de-termine whether inflation occurred before or afterthe upper and lower parts of the flow (to be sam-pled) were solidified, so it is best not to use inflatedflows at all.The “ideal” profile of Sahagian et al. (1989) in-volves thickness of upper and lower vesicularzones, bulk vesicularity profile, and size distribu-tion as a function of stratigraphic position withinthe flow. These distributions depend on flow thick-ness, so there is no single set of values that can becited as “ideal.” However, there are some com-monalities. Vesicles in the lower vesicular zone be-come smaller, and vesicularity decreases upwardfrom the bottom (because of the slowing of thelower crystallization front with time). Vesicles inthe upper vesicular zone become larger, and vesic-ularity increases downward from the top (becauseof the upper crystallization front trapping rising andcoalescing bubbles as it slows) (Sahagian 1985). Inflows in the 1–2 m range, the size distribution inthe lower part of the upper vesicular zone shouldbe bimodal (because of coalescence), and for thickerflows it can be trimodal (Sahagian et al. 1989). Ifthe above features have the correct distributionsfor a given flow thickness, the field geologist canbe reasonably certain that there were no post-emplacement processes such as inflation or defla-tion to invalidate the analysis for paleoelevationstudies.Bondre (2003) suggests using the thickness of theupper crust (Hon et al. 1994) as a measure of flowthickness, but the suggested relation depends ontime during cooling and is not readily measured inthe field for paleoelevation studies. An alternativemight be to estimate the bulk vesicularity in theupper vesicular zone. Simple emplacement shouldideally lead to an increase in vesicularity withdepth from the top (Sahagian 1985). In contrast,observations have suggested that inflated flowsshow a decrease in vesicularity with depth (Cash-man and Kauahikaua 1997). If this is true, thismight also be used as a discriminator between sim-ple and inflated flows.The “bottom line” indication of our ability toidentify simply emplaced flows is figure 9 in Sa-hagian et al. (2002a), which tests the analysis ofrecent flows along the flanks of Mauna Loa, Ha-waii. If we were to accept Bondre’s (2003) assertionthat these flows were inflated after solidification ofthe upper and lower parts that we sampled, thenwe would need to correct for this by moving all thedata points up in elevation. This would move thedata cluster away from their actual elevations, asdepicted by the line. Another way to con-slopep 1sider this is that if there had been any inflation (ordeflation), the data points would lie consistentlybeneath (or above) the line with . Theslopep 1agreement of our analysis with the actual eleva-tions from which the samples were taken is theacid test of our ability to select appropriate flowsfor sampling. The same selection criteria were usedon the Colorado Plateau (Sahagian et al. 2002b).In general, no single feature of the vesicularityprofile should be considered as reliable alone, andall observable aspects of the profile should be ex-amined in concert to establish simple emplace-ment. We take the conservative approach of notattempting to correct for inflated (or deflated) flowsbut simply of disqualifying such flows from ouranalyses. As further investigations lead to a moredetailed understanding of flow emplacement pro-cesses, it may be possible to relax some of the strin-gent restrictions we have placed on our samplingsites, thus opening up a much wider range of po-tential field applications and increasing the effi-ciency by which large numbers of samples can becollected for analysis.R E F E R E N C E S C I T E DBondre, N. 2003. Analysis of vesicular basalts and lavaemplacement processes for application as a paleoba-rometer/paleoaltimeter: a discussion. J. Geol. 111:499–502.Cashman, K., and Kauahikaua, J. 1997. Re-evaluation ofvesicle distributions in basaltic lava flows. Geology25:419–422.Hon, K.; Kauahikaua, J.; Denlinger, R.; and Mackay, K.1994. Emplacement and inflation of pahoehoe sheetflows: observations and measurements of active lavaflows on Kilauea Volcano, Hawaii. Geol. Soc. Am.Bull. 106:351–370.Ketcham, R., and Carlson, W. 2001. Acquisition, opti-mization and interpretation of x-ray computed tom-ographic imagery: applications to the geosciences.Comput. Geosci. 27:381–400.Proussevitch, A., and Sahagian, D. 2001. Recognition andseparation of discrete objects within complex 3D vox-elized structures. Comput. Geosci. 27:441–454.Sahagian, D. 1985. Bubble migration and coalescenceThis content downloaded from 132.177.229.130 on November 09, 2018 06:32:03 AMAll use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).504 D I S C U S S I O N A N D R E P L Yduring the solidification of basaltic lava flows. J. Geol.93:205–211.Sahagian, D.; Anderson, A. T.; and Ward, B. 1989. Bubblecoalescence in basalt flows: comparison of a numericalmodel with natural examples. Bull. Volcanol. 52:49–56.Sahagian, D.; Proussevitch, A.; and Carlson, W. 2002a.Quantitative analysis of vesicular basalts for appli-cation as a paleobarometer/paleoaltimeter. J. Geol.110:671–685.———. 2002b. Timing of Colorado Plateau Uplift: initialconstraints from vesicular basalt-derived paleoeleva-tions. Geology 30:807–810.This content downloaded from 132.177.229.130 on November 09, 2018 06:32:03 AMAll use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).

Analysis of Vesicular Basalts and Lava Emplacement Processes for Application as a Paleobarometer/Paleoaltimeter: A Reply

University of New Hampshire

University of New Hampshire
University of New Hampshire Scholars' Repository
Faculty Publications
7-1-2003
Analysis of Vesicular Basalts and Lava
Emplacement Processes for Application as a
Paleobarometer/Paleoaltimeter: A Reply
Dork L. Sahagian
Lehigh University
Alexander A. Prusevich
University of New Hampshire, Durham, alex.proussevitch@unh.edu
William D. Carlson
University of Texas at Austin
Follow this and additional works at: https://scholars.unh.edu/faculty_pubs
This Article is brought to you for free and open access by University of New Hampshire Scholars' Repository. It has been accepted for inclusion in
Faculty Publications by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact
nicole.hentz@unh.edu.
Recommended Citation
Sahagian, D., Proussevitch, A., & Carlson, W. (2003). Analysis of Vesicular Basalts and Lava Emplacement Processes for Application as
a Paleobarometer/Paleoaltimeter: A Reply. The Journal of Geology, 111(4), 502-504. doi:10.1086/375278
[The Journal of Geology, 2003, volume 111, p. 502–504]  2003 by The University of Chicago. All rights reserved. 0022-1376/2003/11104-0009$15.00
502
Analysis of Vesicular Basalts and Lava Emplacement Processes for
Application as a Paleobarometer/Paleoaltimeter: A Reply
D. Sahagian, A. Proussevitch,1 and W. Carlson2
Climate Change Research Center, Institute for the Study of Earth, Oceans, and Space, and Department of Earth
Sciences, University of New Hampshire, Durham, New Hampshire 03824, U.S.A.
(e-mail: dork.sahagian@uhn.edu)
The use of vesicular basalts as a tool for the mea-
surement of paleoelevation is based on the calcu-
lation of atmospheric pressure from the difference
between vesicle sizes in the tops and bottoms of
flows. Assuming that the bubbles were a well-
mixed population at eruption from the vent, the
difference in size is caused by the pressure of the
lava overburden relative to external atmospheric
pressure. Thus, if the flow thickness and density
are known or measured and the size distributions
can be determined, atmospheric pressure and thus
elevation can be calculated. In this analysis, the
two most difficult (and thus critical) measurements
are the vesicle sizes and flow thickness. A method
to measure the former has been developed (Ketch-
am and Carlson 2001; Proussevitch and Sahagian
2001) so that the remaining practical limitation on
using the technique of Sahagian et al. (2002a,
2002b) is the ability of the field geologist to deter-
mine that the measured flow thickness represents
the thickness of the flow at the time that the upper
and lower 10 cm or so (from which samples would
be taken) solidified to “lock in” the vesicle sizes.
The primary concern regarding thickness is that
there may have been deflation or inflation of the
flow after the top and bottom solidified (Bondre
2003). While it may be optimal to identify a thin
lobe or breakout where late-stage inflation would
not be expected, as suggested by Bondre (2003), this
is not always possible because of incomplete field
exposures, especially for older flows. Consequently,
flows must be examined critically in the field in
cross section. For the study of Sahagian et al.
(2002a) in Hawaii, we did not sample strictly from
Manuscript received January 18, 2003.
1 Department of Earth Sciences, University of New Hamp-
shire, Durham, New Hampshire 03824, U.S.A.
2 Department of Geological Sciences, University of Texas,
Austin, Texas 78712, U.S.A.
thin lobes or breakouts but rather from all parts of
the flows—near the vent, on the flank of the vol-
cano, and around Hilo. The criteria for establishing
simple emplacement were unrelated to lateral ge-
ometry but rather were based on vesicle population
structure in vertical cross section. The character-
istic features of simple emplacement can be rec-
ognized in flows of any age or exposure quality,
provided there is a complete cross section through
the flow.
The question becomes how to identify simple
emplacement in the field. In flow cross sections,
there are often confounding features—such as mul-
tiple vesicular zones, discontinuities in the vesic-
ularity profile, very large vesicles, pipes, evidence
of shear deformation, and “xenoliths” of previously
solidified lava—that should represent a red flag to
the field geologist and make it easy to disqualify
flows with such complexities. The absence of such
obvious features is not necessarily a guarantee that
the flow experienced simple emplacement, so the
vesicularity profile, thickness of upper vesicular
zone relative to flow thickness, and size distribu-
tion profiles must be critically examined relative
to the profile expected for simple emplacement.
Inflation, even if continuous rather than pulsed,
would disrupt the rise and coalescence of bubbles
that result in the appropriate bimodal or trimodal
size distribution in the upper vesicular zone and is
identifiable on that basis. If inflation occurs rela-
tively early in the emplacement process, before so-
lidification of the upper and lower 10 cm or so of
the flow (and before significant bubble rise and co-
alescence), the vesicle sizes will adjust to accom-
modate the “new” thickness, in which case the
analysis would apply to the inflated thickness of
the flow, and paleoelevation studies could be
conducted with the thickness measured in the
field. Also, once there is a thick upper crust that
makes it possible to generate internal lava pres-
This content downloaded from 132.177.229.130 on November 09, 2018 06:32:03 AM
All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).
Journal of Geology D I S C U S S I O N A N D R E P L Y 503
sures greater than hydrostatic (Hon et al. 1994), it
no longer matters what the internal pressure is be-
cause the upper (and lower) vesicles have been fro-
zen in already. However, it is not clear how to de-
termine whether inflation occurred before or after
the upper and lower parts of the flow (to be sam-
pled) were solidified, so it is best not to use inflated
flows at all.
The “ideal” profile of Sahagian et al. (1989) in-
volves thickness of upper and lower vesicular
zones, bulk vesicularity profile, and size distribu-
tion as a function of stratigraphic position within
the flow. These distributions depend on flow thick-
ness, so there is no single set of values that can be
cited as “ideal.” However, there are some com-
monalities. Vesicles in the lower vesicular zone be-
come smaller, and vesicularity decreases upward
from the bottom (because of the slowing of the
lower crystallization front with time). Vesicles in
the upper vesicular zone become larger, and vesic-
ularity increases downward from the top (because
of the upper crystallization front trapping rising and
coalescing bubbles as it slows) (Sahagian 1985). In
flows in the 1–2 m range, the size distribution in
the lower part of the upper vesicular zone should
be bimodal (because of coalescence), and for thicker
flows it can be trimodal (Sahagian et al. 1989). If
the above features have the correct distributions
for a given flow thickness, the field geologist can
be reasonably certain that there were no post-
emplacement processes such as inflation or defla-
tion to invalidate the analysis for paleoelevation
studies.
Bondre (2003) suggests using the thickness of the
upper crust (Hon et al. 1994) as a measure of flow
thickness, but the suggested relation depends on
time during cooling and is not readily measured in
the field for paleoelevation studies. An alternative
might be to estimate the bulk vesicularity in the
upper vesicular zone. Simple emplacement should
ideally lead to an increase in vesicularity with
depth from the top (Sahagian 1985). In contrast,
observations have suggested that inflated flows
show a decrease in vesicularity with depth (Cash-
man and Kauahikaua 1997). If this is true, this
might also be used as a discriminator between sim-
ple and inflated flows.
The “bottom line” indication of our ability to
identify simply emplaced flows is figure 9 in Sa-
hagian et al. (2002a), which tests the analysis of
recent flows along the flanks of Mauna Loa, Ha-
waii. If we were to accept Bondre’s (2003) assertion
that these flows were inflated after solidification of
the upper and lower parts that we sampled, then
we would need to correct for this by moving all the
data points up in elevation. This would move the
data cluster away from their actual elevations, as
depicted by the line. Another way to con-slope p 1
sider this is that if there had been any inflation (or
deflation), the data points would lie consistently
beneath (or above) the line with . Theslope p 1
agreement of our analysis with the actual eleva-
tions from which the samples were taken is the
acid test of our ability to select appropriate flows
for sampling. The same selection criteria were used
on the Colorado Plateau (Sahagian et al. 2002b).
In general, no single feature of the vesicularity
profile should be considered as reliable alone, and
all observable aspects of the profile should be ex-
amined in concert to establish simple emplace-
ment. We take the conservative approach of not
attempting to correct for inflated (or deflated) flows
but simply of disqualifying such flows from our
analyses. As further investigations lead to a more
detailed understanding of flow emplacement pro-
cesses, it may be possible to relax some of the strin-
gent restrictions we have placed on our sampling
sites, thus opening up a much wider range of po-
tential field applications and increasing the effi-
ciency by which large numbers of samples can be
collected for analysis.
R E F E R E N C E S C I T E D
Bondre, N. 2003. Analysis of vesicular basalts and lava
emplacement processes for application as a paleoba-
rometer/paleoaltimeter: a discussion. J. Geol. 111:
499–502.
Cashman, K., and Kauahikaua, J. 1997. Re-evaluation of
vesicle distributions in basaltic lava flows. Geology
25:419–422.
Hon, K.; Kauahikaua, J.; Denlinger, R.; and Mackay, K.
1994. Emplacement and inflation of pahoehoe sheet
flows: observations and measurements of active lava
flows on Kilauea Volcano, Hawaii. Geol. Soc. Am.
Bull. 106:351–370.
Ketcham, R., and Carlson, W. 2001. Acquisition, opti-
mization and interpretation of x-ray computed tom-
ographic imagery: applications to the geosciences.
Comput. Geosci. 27:381–400.
Proussevitch, A., and Sahagian, D. 2001. Recognition and
separation of discrete objects within complex 3D vox-
elized structures. Comput. Geosci. 27:441–454.
Sahagian, D. 1985. Bubble migration and coalescence
This content downloaded from 132.177.229.130 on November 09, 2018 06:32:03 AM
All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).
504 D I S C U S S I O N A N D R E P L Y
during the solidification of basaltic lava flows. J. Geol.
93:205–211.
Sahagian, D.; Anderson, A. T.; and Ward, B. 1989. Bubble
coalescence in basalt flows: comparison of a numerical
model with natural examples. Bull. Volcanol. 52:49–56.
Sahagian, D.; Proussevitch, A.; and Carlson, W. 2002a.
Quantitative analysis of vesicular basalts for appli-
cation as a paleobarometer/paleoaltimeter. J. Geol.
110:671–685.
———. 2002b. Timing of Colorado Plateau Uplift: initial
constraints from vesicular basalt-derived paleoeleva-
tions. Geology 30:807–810.
This content downloaded from 132.177.229.130 on November 09, 2018 06:32:03 AM
All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).


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Analysis of Vesicular Basalts and Lava Emplacement Processes for Application as a Paleobarometer/Paleoaltimeter: A Reply

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