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词条 Zamama (volcano)
释义

  1. Overview of the Voyager and Galileo missions

  2. Volcanism on Zamama

     Volcanic topography  Surface changes  Temperature  Composition  Volcanic parameters 

  3. Comparison and evolution

     Comparisons with Ionian and terrestrial volcanoes  Evolution of Ionian shield volcanoes 

  4. Future Io exploration

  5. References

  6. Further reading

  7. External links

{{Use dmy dates|date=May 2015}}

Zamama is an active volcanic center on Jupiter{{'s}} moon Io.[1][2] This volcanic center erupted after the Voyager 1 flyby in 1979, making it one of the few planetary volcanoes known to have activated during this generation's lifetime. Further analysis and study by the Galileo spacecraft helped with the overall study of Io's volcanism. Galileo located it on Io at {{coord|21|N|173 |W|globe:io_type:landmark_source:gpn|display=inline,title|notes=[1][3]}}. Zamama has a fissure-fed-type flow that is {{convert|150|km|mi|abbr=on}} long with temperatures of {{convert|1100|K|C F|lk=in}},[1] and the volcanic center site has explosive and effusive eruption characteristics.[6] The flow appears to be emanating from the Promethean-type volcano.

Remote sensing instruments built on the Galileo spacecraft—the Near-Infrared Mapping Spectrometer (NIMS), Solid-State Imager (SSI), Photopolarimeter-Radiometer (PPR)—collect and analyze volcanism on Io's surface. Since there are no samples collected from Io, all of the interpretations are made by studying albedo effects, morphology and/or spectral variations in Galileo data. Furthermore, Geomorphologic analysis is strictly used to study such specific planetary structures.[1][4]

Overview of the Voyager and Galileo missions

Most of the data acquired from the Jovian moon Io was derived from geomorphologic interpretations of orbital imaging. Voyager 1 and Galileo both used thermal remote sensing to accomplish this task. Thermal remote sensing is a branch of remote sensing which deals with processing and interpretations of data in the thermal infrared (TIR) region of the electromagnetic (EM) spectrum. Zamama is a hotspot/volcanic center among 61 active volcanic centers on Io.[5] These were observed by the Voyager flybys, by Galileo, and by ground-based observations. Zamama was first observed by Galileo,[5] which identified two types of volcanic activity: persistent and sporadic.[5] The NIMS instrument detected activity at Zamama lasting longer than one year; therefore, it is considered the persistent type.[5] It has only been NIMS-detected five times, but NIMS-observed nine times. This lower incidence of detection could be due to observational constraints or temporary waning of activity.[5]

Volcanism on Zamama

Volcanic topography

Io is one of the most challenging Jovian moons for which to establish topography. A couple techniques aided in the making of Io's topography, such as "3D" stereo photogrammetry (SP) and "2D" photoclinometry (PC).[6] Ionian volcanoes have been poorly characterized because of their volcanic construct, which is different than well-studied planetary volcanoes such as those on Mars. Two common flow field morphologies have been identified on Io:[6]

  • Large broad irregular flows (flow sheets).
  • Radially centered flow fields.

The Zamama active volcanic center is characterized morphologically by a radially centered flow field. Multiple steep-sided shield volcanoes lie in this area:

  • Zamama A (18°N, 175°W), is about {{convert|40|km|mi|abbr=on}} wide, {{convert|1.5|km|mi|abbr=on}} high, and has an average slope of 40°. Slope and height were estimated by PC. It extends about {{convert|140|km|mi|abbr=on}} east and beyond the topographic margin of the observed steep-sided shield.[6] Zamama A is the source of the Zamama flow field.[17] The origin of volcanism is both siliceous and sulfuric, although Zamama originates from a Prometheus-type plume.[17]
  • Zamama B is located {{convert|75|km|mi|abbr=on}} southeast of Zamama A, and is about {{convert|40|km|mi|abbr=on}} wide and {{convert|1|-|1.5|km|mi|abbr=on}} high. Height was estimated by PC shadow measurements.[6]
  • Zamama C (15°N, 170°W) is located {{convert|175|km|mi|abbr=on}} southeast of the Zamama volcanic center, is about {{convert|250|m|ft|abbr=on}} high, and has a slope that ranges between 3°-5°. Height was determined by PC.[6]

Surface changes

Zamama appears to have been inactive during the 1979 Voyager 1 visit, or, it may have been buried by the Volund deposits. In contrast, Zamama appeared as a very active hot spot during the Galileo observations. Zamama has shown three notable surface changes in the SSI collected images. Images show them as bright rings, placed within the dark lava flows, with diameters of about {{convert|370|km|mi|abbr=on}}. In addition, new black rings were deposited north and northeast of the central prominent eruption. This most prominent central eruption was the first to take place (18° N, 171° W). The total area changed was about {{convert|136000|km2|mi2|abbr=on}}. Second, a new eruption caused broadening in the central dark deposits of the western side and new bright rings were deposited along the margins of the lava flows. The total area effected was about {{convert|37000|km2|mi2|abbr=on}}. Third, Zamama's third plume was actively erupting while Galileo was on its 14th orbit around Jupiter. New deposits enlarged to {{convert|150|±|5|km|mi|abbr=on}} and are centered east of the eruptive center. Total affected area was about {{convert|96000|km2|mi2|abbr=on}}.[7]

Temperature

Galileo{{'s}} NIMS instrument collected data on volcanic emissions to analyze the power output. A two-temperature model is used to determine the temperature and power output. Models have shown that Zamama has a temperature of {{convert|1173|±|243|K|C F}}. Pyroclastic flows with high silica content can have temperatures as high as {{convert|1200|C|K F}}. Since Zamama volcanoes have such high temperatures, this indicates siliceous magma. No actual samples of Zamama's magma have been retrieved and processed for composition.[8]

Composition

Lava flows at Zamama suggest that it is a shield volcano with a central vent and a rift zone. The rift zone seems to feed the dark flow field, which appeared in the Galileo visit. The flow field appeared narrow/thin closer to the center, and wide/broad away from the center. This behavior might be due to a change in slope from the volcano rim to the nearby plains. The central vent emanates bright flows, due to sulfurous lava composition or silicate lava coated by sulfurous deposits. The composition of the lava emitted from the volcano is still mysterious.[9]

Volcanic parameters

NIMS data analysis was conducted to determine the variability of thermal emissions from volcanoes on Io—particularly Zamama—for 1,038 days (28 June 1996 to 2 May 1999) and the results showed:[4]

  • Average volumetric rates decreased at the beginning of the period, which indicates a lessening in diffusive activity, or cooling of old flow surface. Later, there was an increase in volcanic activity, indicating the beginning of an eruption.
  • Total power output observed at Zamama was {{val|1.25|e=19|ul=J}}.
  • Average power output was {{val|139.8|ul=GW}}.
  • Total volume erupted through this period was {{convert|3.5|±|1.4|km3|mi3|abbr=on}}.
  • Average volumetric flux was {{convert|39.4|±|15.5|m3/s|ft3/s|abbr=on}}.

Comparison and evolution

Comparisons with Ionian and terrestrial volcanoes

  • Zamama has lower volumetric emission rates compared to various styles of eruptions on Io.[4]
  • Zamama is more powerful than its terrestrial counterparts such as Kīlauea, Hawaii.[4]
  • In general, Io's eruptions have larger volumetric fluxes and active areas than terrestrial volcanoes, compared with volcanoes of the same eruption style.[4]

Evolution of Ionian shield volcanoes

Most Ionian volcanoes start as steep-sided shield volcanoes. After an eruptive construct-building phase, the central region collapses to form a caldera. Since steep-sided shield volcanoes have not been observed inside collapsed calderas, this indicates a failure to reform steep-sided volcanoes after the collapse, which can be associated with various variables such as change in temperature, eruptive rate, and/or lava composition. Failure to reform shield volcanoes is caused by failure to supply magma through the magma chamber. These interpretations might be a sign that current shield volcanoes will follow this pattern and transform to caldera-forming eruptive sites.[6]

Future Io exploration

Williams (2013) suggests the need for a variety of methods for observing Io in the future: "Future Io exploration is recommended to include: 1) a Jupiter-orbiting Io Observer spacecraft of either Discovery-class or New Frontiers-class; 2) a space-based UV telescope with diffraction-limited capability; 3) space-based missions that enable long-term monitoring of Io over a variety of time scales (seconds, minutes, hours, days, months, years); and 4) expanded time for Io observation on ground-based 8- to 10-m class telescopes, particularly those with nighttime Adaptive Optics capability."[10]

References

1. ^1 2 3 {{cite journal |title=Temperature and area constraints of the South Volund volcano on Io from the NIMS and SSI instruments during the Galileo G1 orbit |journal=Geophysical Research Letters |first1=Ashley Gerald |last1=Davies |first2=Alfred S. |last2=McEwen |first3=Rosaly M. C. |last3=Lopes-Gautier |first4=Laszlo |last4=Keszthelyi |first5=Robert W. |last5=Carlson |first6=William D. |last6=Smythe |display-authors=5 |volume=24 |issue=20 |pages=2447–2450 |date=October 1997 |doi=10.1029/97GL02310 |bibcode=1997GeoRL..24.2447D}}
2. ^{{cite journal |title=High-temperature hot spots on Io as seen by the Galileo Solid State Imaging (SSI) experiment |journal=Geophysical Research Letters |first1=Alfred S. |last1=McEwen |first2=Damon P. |last2=Simonelli |first3=David R. |last3=Senske |first4=Kenneth P. |last4=Klaasen |first5=Laszlo |last5=Keszthelyi |first6=Torrence V. |last6=Johnson |first7=Paul E. |last7=Geissler |first8=Michael H. |last8=Carr |first9=Michael J. S. |last9=Belton |display-authors=5 |volume=24 |issue=20 |pages=2443–2446 |date=October 1997 |doi=10.1029/97GL01956 |bibcode=1997GeoRL..24.2443M}}
3. ^{{cite book |title=Volcanism on Io: A Comparison with Earth |publisher=Cambridge University Press |last1=Davies |first1=Ashley Gerard |date=2007 |isbn=978-0-521-85003-2 |bibcode=2007vice.book.....D}}
4. ^1 2 3 4 {{cite conference |url=https://ntrs.nasa.gov/search.jsp?R=20050166890 |title=Thermal Emission Variability of Zamama, Culann and Tupan on Io Using Galileo Near-Infrared Mapping Spectrometer (NIMS) Data |conference=36th Annual Lunar and Planetary Science Conference. 14–18 March 2005. League City, Texas. |last1=Ennis |last2=M. E. |last3=Davies |first3=A. G. |at=1474 |date=March 2005 |bibcode=2005LPI....36.1474E}}
5. ^1 2 3 4 {{cite journal |title=Active Volcanism on Io: Global Distribution and Variations in Activity |journal=Icarus |first1=Rosaly |last1=Lopes-Gautier |first2=Alfred S. |last2=McEwen |first3=William B. |last3=Smythe |first4=P. E. |last4=Geissler |first5=L. |last5=Kamp |first6=A. G. |last6=Davies |first7=J. R. |last7=Spencer |first8=L. |last8=Keszthelyi |first9=R. |last9=Carlson |first10=F. E. |last10=Leader |first11=R. |last11=Mehlman |first12=L. |last12=Soderblom |display-authors=5 |volume=140 |issue=2 |pages=243–264 |date=August 1999 |doi=10.1006/icar.1999.6129 |bibcode=1999Icar..140..243L}}
6. ^1 2 3 4 5 6 {{cite journal |title=Shield volcano topography and the rheology of lava flows on Io |journal=Icarus |last1=Schenk |first1=P. M. |last2=Wilson |first2=R. R. |last3=Davies |first3=A. G. |volume=169 |issue=1 |pages=98–110 |date=May 2004 |doi=10.1016/j.icarus.2004.01.015 |bibcode=2004Icar..169...98S}}
7. ^{{cite journal |title=Surface changes on Io during the Galileo mission |journal=Icarus |first1=Paul |last1=Geissler |first2=Alfred |last2=McEwen |first3=Cynthia |last3=Phillips |first4=Laszlo |last4=Keszthelyi |first5=John |last5=Spencer |volume=169 |issue=1 |pages=29–64 |date=May 2004 |doi=10.1016/j.icarus.2003.09.024 |bibcode=2004Icar..169...29G}}
8. ^{{cite journal |title=Volcanism on Io: Estimation of eruption parameters from Galileo NIMS data |journal=Journal of Geophysical Research |first=Ashley Gerard |last=Davies |volume=108 |issue=E9 |pages=5106–5120 |date=September 2003 |doi=10.1029/2001JE001509 |bibcode=2003JGRE..108.5106D}}
9. ^1 2 {{cite journal |title=Imaging of volcanic activity on Jupiter's moon Io by Galileo during the Galileo Europa Mission and the Galileo Millennium Mission |journal=Journal of Geophysical Research |first1=L. |last1=Keszthelyi |first2=A. S. |last2=McEwen |first3=C. B. |last3=Phillips |first4=M. |last4=Milazzo |first5=P. |last5=Geissler |first6=E. P. |last6=Turtle |first7=J. |last7=Radebaugh |first8=D. A. |last8=Williams |first9=D. P. |last9=Simonelli |first10=H. H. |last10=Breneman |first11=K. P. |last11=Klaasen |first12=G. |last12=Levanas |first13=T. |last13=Denk |display-authors=5 |volume=106 |issue=E12 |pages=33025–33052 |date=December 2001 |doi=10.1029/2000JE001383 |bibcode=2001JGR...10633025K}}
10. ^{{cite conference |url=https://gsa.confex.com/gsa/2013AM/webprogram/Paper228780.html |title=The Future of Io Exploration |conference=Geological Society of America 125th Anniversary Annual Meeting & Expo. 27–30 October 2013. Denver, Colorado. |first=David A. |last=Williams |date=2013 |id=Paper No. 305-6}}

Further reading

  • {{cite journal |title=The Zamama–Thor region of Io: Insights from a synthesis of mapping, topography, and Galileo spacecraft data |journal=Icarus |first1=David A. |last1=Williams |first2=Laszlo P. |last2=Keszthelyi |first3=Paul M. |last3=Schenk |first4=Moses P. |last4=Milazzo |first5=Rosaly M. C. |last5=Lopes |first6=Julie A. |last6=Rathbun |first7=Ronald |last7=Greeley |display-authors=5 |volume=177 |issue=1 |pages=69–88 |date=September 2005 |doi=10.1016/j.icarus.2005.03.005 |bibcode=2005Icar..177...69W}}
  • {{cite journal |title=Silicate Cooling Model Fits to Galileo NIMS Data of Volcanism on Io |journal=Icarus |first1=Ashley Gerard |last1=Davies |first2=Rosaly |last2=Lopes-Gautier |first3=William D. |last3=Smythe |first4=Robert W. |last4=Carlson |volume=148 |issue=1 |pages=211–225 |date=November 2000 |doi=10.1006/icar.2000.6486 |bibcode=2000Icar..148..211D}}

External links

  • {{commons category-inline|Zamama (volcano)}}
{{Io}}

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