Dr. Peter J. Mouginis-Mark
Planetary Geosciences Division
University of Hawaii
2525 Correa Road
Honolulu, HI 96822
Co-Investigators:
V.H. Kaupp, University of Arkansas
H.C. MacDonald, University of Arkansas
W.P. Waite, University of Arkansas
Eruptive Styles Of Basaltic Shield Volcanoes From Shuttle Imaging Radar-C (SIR-C)
and X-SAR Data
OBJECTIVES
To provide a comprehensive understanding of the distribution of volcanic materials
on classic examples of balsaltic shield volcanoes in Hawaii, Reunion Island (Indian
Ocean) and Galapagos (Eastern Pacific).
Interpret the preserved eruptive history of each volcano, draw contrasts between each
test site in terms of the role of the tectonic setting on basaltic volcanism, and
make inferences about the internal structure of the volcano and its magma chamber.
PROGRESS
Since the
SRL-2
mission (October 1994), we have recognized the importance of the repeat-orbit
phase of the mission for conducting new volcanological research with interferometric
radar data. Over the last eight months we have therefore undertaken a vigorous program to develop our own interferometric
SAR
processing scheme at the University
of Hawaii through a close collaboration with Howard Zebker and Paul Rosen at
JPL.
The processing scheme that we have developed is based on a program in use at
JPL,
and on the mathematics outlined by Curlander (1991). From raw
SIR-C
data we can now construct
images, co-register repeat-pass images, produce interferograms between images, unwrap
interferogram phase, and minimize baseline uncertainties. We have performed the mapping from interferometric phase to topography, and calibrated the topography to
produce digital elevation models. Our ultimate processing goal, which we expect
to reach by the end of 1995, is to use repeat-pass interferometry to produce quantitative
phase correlation maps in order to describe surface change on volcanoes such as Kliuchevskoi
(Kamchatka). Our interferometry work in Hawaii mirrors studies conducted at
JPL,
and we have collaborated on one of their papers (Zebker et al., submitted to Science) on the surface changes due to the emplacement of new lava flows at Kilauea volcano
during
SRL-2
(see Fig. 1).
For test data we have worked with
SIR-C
data for our "Super Site" on Isabela Island
(Galapagos). Figs. 2 and 3 demonstrate our current capabilities to perform this
interferometry work, which allows us to go from the raw data to a
DEM.
This
DEM
is being used to study the relationship between lava flow widths and slopes (a good indicator
of changing lava flow rheology) as well as test our phase unwrapping algorithms for
SIR-C
via a comparison with the
TOPSARDEM
that was obtained as part of the 1993
South America deployment of the
NASADC-8
aircraft. As our
SIR-C
investigations advance
from algorithm development to scientific application, we shall concentrate on creating
images and DEMs for Kliuchevskoi, Taal (Philippines), the Virunga Chain (Zaire),
and Piton dela Fournaise (Reunion Island), and on deformation mapping of Kilauea and Kliuchevskoi.
For the Galapagos, by comparing DEMs from
SIR-C
data with pre- and post-eruption
SPOT
images (together with
TOPSAR
results), we will investigate topographic control of lava flows.
As a parallel activity, we expect to be able to demonstrate within a few months a
fully-functional
SAR
processing scheme together with full satellite downlink capabilities
(using our own X-band ground station). With the capability to process
SIR-C
data,
and with the ability also to downlink ERS and JERS data, we will be in a good position
to support any future
NASA
radar missions, including any
SRL-3
or TOPSAT mission.
This university-based capability should be particularly useful as
NASA
attempts
to find low-cost methods for radar data reception and processing in order to fly these future
missions.
We have obtained 11 data takes over Hawaii (including Mauna Loa, Kilauea and Haleakala
-- all places where we have on-going research), and 31 data takes over other volcanoes.
As part of this investigation, a total of 27 interferometric data sets have also been obtained or are requested, making 69 data requests in all. Currently, we have
research underway using
SIR-C
data to investigate the relationship between extensional
tectonism and volcanism at Erta Ale (Ethiopia), the structure of Taal caldera and
the regional distribution of volcanic land forms in the Virunga volcanic chain. The
Virunga chain includes Nyamuragira and Nyiragongo volcanoes, and gives us the opportunity
to study the radar scattering properties, the noise floor of the radar data, and
the radar system calibration in an area where the distribution of flow types and vegetation
is poorly known, thereby building on our experience with
SIR-C
data at Kilauea.
We have
SIR-C
data for the Virunga Chain that were obtained at three different pulse
bandwidths and two look-directions, and have on order a
SPOT
multispectral image for
the same area. In addition to describing the volcanology of this area, we will also
study the effects of different pulse bandwidths for mapping the numerous cinder cones
and lava flows in this rarely studied area.
SIGNIFICANT RESULTS
As we work through the radar interferometry data sets, we are starting to see some
fascinating new things. Our paper (Zebker et al., submitted to Science
) shows for the first time how an orbital radar can be used to measure the daily change
in area of new lava flows on Kilauea volcano, Hawaii. Such data provide new insights
into the eruption characteristics of the volcano, and the growth of lava flow fields. By approximating the average thickness of the flow to 50 cm, we have estimated
an average effusion rate of ~2 cubic meters per second over the four-day observation
period. Furthermore, the derivation of the phase correlation maps (needed to detect
new lava flow surfaces) also revealed some unexpected phenomena that we believe are
due to atmospheric moisture. This was totally unexpected, and we plan to process
additional interferometry pairs as fast as we can in order to search similar phenomena
in different climatic settings.
As a part of our efforts to educate the volcanology community on the value of orbital
radars, and
SIR-C
in particular, we have published a general review (in Earth Observation Quarterly
) of radar interferometry in volcanology, and have a review article in press in IEEE Trans. Geosci. Rem. Sen.
The P.I. has also served on the
NASANRC
Review Panel (John McElroy, Chair) advocating
a new
NASA
interferometric radar mission. Invited papers on the
SIR-C
results have
been given at the 1994 GSA meeting (Seattle) and the 1995 IUGG General Assembly (Boulder, CO). Another review will be given at the All-Union special session on "Radar
Interferometry" at the Fall 1995
AGU
meeting in San Francisco.
Surface change at Kliuchevskoi volcano, Kamchatka, during the October 1994 eruption.
As luck would have it, there was a major explosive eruption of Kliuchevskoi volcano
five hours after the launch of
SRL-2.
While most of the explosive activity took
place during the early parts of the mission, pyroclastic flows and mudflows were reported
during the repeat-orbit phase of the mission between October 7th - 10th. We are
currently processing these interferometric data to search for surface change. If
we find any, we will place these results into the general context of the eruption with the
aid of reports made by other volcanologists on the ground and images taken by the
SRL-2
crew during the mission. This work is in an early phase, but will be submitted
to Bulletin Volcanology either as a complete study, or as a component of a paper on the
use of radar-derived digital elevation models and surface change detection.
For our Galapagos Super Site, we have used the
SIR-C
data to help with the mapping
of Fernandina volcano, particularly in determining flow types. The goal of this
project is to determine the long-term magma production rates and eruption patterns
of the volcano. This is being done by mapping the distribution of flows of various relative
ages, mapping the distribution of eruptive vents, and by calculating the volumes
of the flows of these various ages. Calculating the volumes requires knowledge of
the flow thicknesses, and this is where we are using
TOPSAR
data. So far only the volumes
of the youngest flows have been determined, and they total 25.5 cubic kilometers.
They have been preferentially erupted from the upper and lower SE and NW flanks.
One result of having the good topography is that it has highlighted the fact that there are
essentially no eruptive vents on the steeper slopes, which no doubt reflects some
aspect of the stress field within the volcanic edifice. This work is being prepared
for publication in the special
SIR-C
issue of J. Geophysical Research
.
FUTURE PLANS
Our plans for the next two years are heavily focused on the analysis of the interferometry
data, both for the detection of surface change and atmospheric effects (i.e., analysis
of the phase correlation data) and on the derivation and analysis of the digital elevation models that we will produce. We have a specific set of priorities and
collaborations planned for these studies and intend that each of these investigations
will result in a manuscript being submitted for publication:
Kliuchevksoi volcano, Kamchatka (SRL-2 data takes 121.10, 137.10, 153.10 and 169.20,
all of which are in-hand). We wish to study the later parts of the eruption, searching
for evidence of moving pyroclastic flows, mudflows, and the waning phases of the
eruption plume. Quantitative decorrelation maps will be produced from the
SRL-2
data
collected on October 7th, 8th, 9th and 10th, 1994 to show how the flows may have
moved on a daily basis. Through this study we hope to learn more about the emplacement
of these flows -- we expect to see changes not only at the leading edge but also in the
up-slope parts of the flow if the flow is a mudflow that remained fluid during to
the release of melt water from the snow-capped peak of the volcano, as suggested
from our inspection of the accompanying hand-held photography obtained by the crew of STS-68.
Morphology and structure of the Virunga volcanic chain, Africa (SRL-2 data takes 154.90
and 170.90). These data encompass virtually the entire Virunga volcanic field, including
the recently active Nyiragongo volcano of Zaire. Parts of Nyamuragira volcano lie within the interferometry pair, and all parts of the volcano were imaged as part
of the multilook data (SRL-1
DT
58.60, 171.10, SRL-258.61 and 154.90). We plan to
produce a
DEM
for the eastern area of the Virunga volcanic field, which includes
the Karisoke Research Center -- home of the endangered mountain gorillas -- and to use this
DEM
to study the distribution of the maar volcanoes in this area as a function of
elevation. Here we wish to use the elevation data to help us remotely discriminate
between cinder cones ("dry" eruptions at relatively high elevations) and maar cones ("wet"
eruptions at lower elevations) close to nearby Lake Kivu; there are many dozens of
cones surrounding the main volcanoes and we hope to deduce some structural aspects
of this mono-genetic volcanic field through a study of cone volume and size of the summit
craters. In addition, there are some unusually thick lava flows on some of the volcanoes
that can be seen in the multilook data; we want to measure their slopes on the
DEM
to help with rheological studies of flows. Nyiragongo and Nyamuragira are characterized
by extremely fluid lava flows that can travel long distances very quickly, posing
an extreme hazard for nearby populated areas, such as Goma (and the surrounding Rwandan refugee camps). Also, the formation of Lake Kivu has heightened the risk of
explosive activity due to magma/groundwater interactions. Although volcanic hazards
mitigation is largely beyond the scope of this study,
SIR-C
data can provide the
basis for geologic maps of the region, particularly in otherwise accessible areas. This
study will provide a regional context for field observations that can be used by
other investigators to further understand the past behavior and future risks in this
area.
Structure of Taal volcano (SRL-2 data takes 126.30, 142.30, and 158.30 all of which
have already been requested). In collaboration with Dr. Stephen Self (Univ. Hawaii)
and Dr. R. Punongbayan (Philippine Volcano Observatory), we plan to create a digital
elevation model of Taal volcano in order to investigate the structure of southwestern
Luzon island, Philippines. Detailed knowledge of the topography will greatly aid
our analysis of the erosional characteristics of the ignimbrite sheets that dominate
the area surrounding Taal caldera. Some areas of deeply eroded (steep slopes?) and other
areas of relatively shallow valleys (lower slopes?) can be identified in individual
SIR-C
images. Our main study area is the Taal ignimbrite sheet north of the caldera,
which is extremely difficult to map on the ground due to dense vegetation and the lack
of roads.
Piton de la Fournaise, Reunion Island was our third original
SIR-C/X-SAR
target.
During the last 3 months, we have been discussing with Jean-Francois Lenat (Center
for Volcanology Research, Clermont Ferrand, France) the possibility of detecting
changes in the large-scale morphology of the volcano between 1990 (when he produced a
DEM
of
the volcano using
SPOT
stereo data) and 1994 (the
SRL-2
interferometry pair from
Data Takes 146.60 and 162.60, both already requested). Because this volcano erupts
almost every year, there is a good possibility that we will be able to detect differences
in the volume of the summit crater and/or flank flows. This will also be a valuable
test for comparing DEMs produced from photogrammetric data with DEMs derived via
interferometry methods.
We have had several requests for producing digital elevation models of other volcanoes,
partly in support of our
EOS
interdisciplinary investigation, and partly to assist
our colleagues in the international volcanology community. Mt. Etna (SRL-2 data
takes 141.10 and 157.10 both requested) is a key area of interest for Dave Pieri and Vince
Realmuto (both at
JPL)
and Dave Rothery, John Murray and Bill McGuire (all in England).
Detailed knowledge of the topography of Etna is required for rheological studies of the numerous lava flows on the flanks, as well as for sulfur dioxide retrievals
using
TIMS
data. Ray Punongbayan is very interested in the production of a
DEM
of
Pinatubo (SRL-2 data takes 126.30, 142.30, and 158.30) because of the continuing
hazards due to lahars on this volcano. Vesuvius (DT 130.40, 146.40, and 162.40 all requested)
is a high priority for Italian and German members of the X-SAR Team, since they wish
us to produce a
DEM
using our code that can then be compared to their result. In
addition, we already have a
TOPSARDEM
for Vesuvius, and will take this opportunity
to compare our
SRL-2
topographic map with these aircraft measurements.
PUBLICATIONS
Evans, D. L., J. Apel, R. Arvidson, R. Binschadler, F. Carsey, J. Dozier, K. Jezek,
E. Kasischke, F. Li, J. Melack, B. Minster, P. Mouginis-Mark, and J. van Zyl. Spaceborne
synthetic aperture radar: Current status and future directions.
NASA
Tech. Mem.
4679, 1995.
Mouginis-Mark, P.J. Analysis of volcanic hazards using radar interferometry. Earth Observation Quarterly
, No. 47, p. 6 - 10, 1995.
Mouginis-Mark, P.J. Preliminary observations of volcanoes with the
SIR-C
radar.
IEEE Trans. Geosci. Rem. Sen.
, in press, April 1995.
Zebker, H. A., P. Rosen, S. Hensley, and P. J. Mouginis-Mark. Analysis of active
lava flows on Kilauea volcano, Hawaii, using
SIR-C
radar correlation measurements.
Submitted to Science
, August 1995.
Students Supported:
Ph.D. dissertation completed:
"Frequency Analysis of SAR: Optimization for Imaging Unvegetated Lava Surfaces" C.
M. Ting, Ph. D. Dissertation, University of Arkansas, May 1995.
M.S.E.E. thesis completed:
"Multi-resolution Decomposition of Radar Images Using Wavelet Transforms" S. Ramamurthi,
M.S.E.E. Thesis, University of Arkansas, December 1994.
Ph.D. dissertation in progress:
Title: TBD. J. F. Hug, University of Arkansas, September 1996 (projected).
MSc dissertation in progress:
Title: TBD. S. Siddiqui, University of Hawaii, December 1996 (projected).
Figure Captions
Figure 1 (554K GIF):
Radar detection of surface change at Kilauea volcano, Hawaii, during the
repeat-orbit phase of the mission. Top left: panel shows the lava flow field down
slope of Pu'u O'o volcano on October 9, 1994. Arrows connect parts of the flow field
to the same areas on the radar phase diagram. Top right: Details of active flow; arrow
connects this flow to the same area seen in the radar phase image. Flow thickness
is about 50 cm. Bottom three panels show radar phase correlation maps for period
October 7-10 for the three 24-hour periods indicated. Zero phase correlation corresponds
to the three active flow fields (Flow regions 1, 2, and 3). Other areas that are
decorrelated are the vegetated slopes of the volcano.
Figure 2 (580K GIF):
Examples of the radar processing capabilities that have been developed at
the University of Hawaii. Input data are the raw reformatted signal data provided
by
JPL.
We can process these data to produce the
SAR
backscatter image (top left),
create a raw radar interferogram (top right), display these two data sets together (bottom
left) and generate a digital elevation model via our own phase unwrapping algorithm
(bottom right). The test data that we display here are for part of Alcedo volcano,
which is a part of our
SIR-C
supersite in the Galapagos Islands.
Figure 3 (432K GIF):
Oblique perspective view of Alcedo volcano, Galapagos Islands, generated
by combining our in-house produced
DEM
and the radar backscatter image. View is
from the northeast.