Weather radar observations of the Hekla 2000 eruption cloud, Iceland

The Hekla eruption cloud on 26–27 February 2000 was the first volcanic cloud to be continuously and completely monitored advecting above Iceland, using the C-band weather radar near the Keflavík international airport. Real-time radar observations of the onset, advection, and waning of the eruption cloud were studied using time series of PPI (plan-position indicator) radar images, including VMI normal, Echotop, and Cappi level 2 displays. The reflectivity of the entire volcanic cloud ranges from 0 to >60 dBz. The eruption column above the vent is essentially characterised by VMI normal and Cappi level 2 values, >30 dBz, due to the dominant influence of lapilli and ash (tephra) on the overall reflected signal. The cloud generated by the column was advected downwind to the north-northeast. It is characterised by values between 0 and 30 dBz, and the persistence of these reflections likely result from continuing water condensation and freezing on ash particles. Echotop radar images of the eruption onset document a rapid ascent of the plume head with a mean velocity of ~30 to 50 m s−1, before it reached an altitude of ~11–12 km. The evolution of the reflected cloud was studied from the area change in pixels of its highly reflected portions, >30 dBz, and tied to recorded volcanic tremor amplitudes. The synchronous initial variation of both radar and seismic signals documents the abrupt increase in tephra emission and magma discharge rate from 18:20 to 19:00 UTC on 26 February. From 19:00 the >45 dBz and 30–45 dBz portions of the reflected cloud decrease and disappear at about 7 and 10.5 h, respectively, after the eruption began, indicating the end of the decaying explosive phase. The advection and extent of the reflected eruption cloud were compared with eyewitness accounts of tephra fall onset and the measured mass of tephra deposited on the ground during the first 12 h. Differences in the deposit map and volcanic cloud radar map are due to the fact that the greater part of the deposit originates by fallout off the column margins and from the base of the cloud followed by advection of falling particle in lower level winds.

[1]  Marcus I. Bursik,et al.  Sedimentation from turbulent jets and plumes , 1996 .

[2]  William I. Rose,et al.  Estimating particle sizes, concentrations, and total mass of ash in volcanic clouds using weather radar , 1983 .

[3]  P. Einarsson,et al.  The Hekla eruption 1980–1981 , 1983 .

[4]  David J. Schneider,et al.  Observations of Volcanic Clouds in Their First Few Days of Atmospheric Residence: The 1992 Eruptions of Crater Peak, Mount Spurr Volcano, Alaska , 2001, The Journal of Geology.

[5]  J. R. Probert-Jones,et al.  The radar equation in meteorology , 1962 .

[6]  Arlin J. Krueger,et al.  The February-March 2000 eruption of Hekla, Iceland from a satellite perspective , 2013 .

[7]  Haraldur Sigurdsson,et al.  Influence of particle aggregation on deposition of distal tephra from the MAy 18, 1980, eruption of Mount St. Helens volcano , 1982 .

[8]  P. Einarsson,et al.  Earthquake activity related to the 1991 eruption of the Hekla volcano, Iceland , 2002 .

[9]  Frank W. Burcham,et al.  EVEN MINOR VOLCANIC ASH ENCOUNTERS CAN CAUSE MAJOR DAMAGE TO AIRCRAFT. , 2002 .

[10]  P. Crutzen,et al.  Atmospheric Change: An Earth System Perspective , 1992 .

[11]  S. McNutt.  Volcanic Tremor Amplitude Correlated with the Volcano Explosivity Index and Its Potential Use in Determining Ash Hazards to Aviation , 1994 .

[12]  A. Krueger,et al.  Ice in the 1994 Rabaul eruption cloud: implications for volcano hazard and atmospheric effects , 1995, Nature.

[13]  Jp Davis,et al.  Bifurcation of volcanic plumes in a crosswind , 1994 .

[14]  William I. Rose,et al.  Measurements of the complex dielectric constant of volcanic ash from 4 to 19 GHz , 1996 .

[15]  Lionel Wilson,et al.  Explosive Volcanic Eruptions-II The Atmospheric Trajectories of Pyroclasts , 1972 .

[16]  Stephen Self,et al.  Atmospheric and environmental effects of the 1783-1784 Laki eruption: A review and reassessment , 2003 .

[17]  William I. Rose,et al.  Real-time C-band radar observations of 1992 eruption clouds from Crater Peak, Mount Spurr Volcano, Alaska , 1995 .

[18]  C. Lacasse.  Influence of climate variability on the atmospheric transport of Icelandic tephra in the subpolar North Atlantic , 2001 .

[19]  David C. Pieri,et al.  Analyses of in‐situ airborne volcanic ash from the February 2000 eruption of Hekla Volcano, Iceland , 2002 .

[20]  Robert A. Page,et al.  Preliminary Analyses of Volcanic Tremor Associated with 1992 Eruptions of Crater Peak, Mount Spurr Volcano, Alaska , 1995 .

[21]  Jens Havskov,et al.  Earthquake prediction research in the South Iceland seismic zone and the SIL project , 1993 .

[22]  S. McNutt.  Volcanic Tremor Amplitude Correlated with Eruption Explosivity and its Potential Use in Determining Ash Hazards to Aviation , 1994 .

[23]  P. Einarsson,et al.  Volcanic tremor related to the 1991 eruption of the Hekla volcano, Iceland , 2003 .

[24]  W. Giggenbach,et al.  The chemistry of fumarolic vapor and thermal-spring discharges from the Nevado del Ruiz volcanic-magmatic-hydrothermal system, Colombia , 1990 .

[25]  Geoffrey Ingram Taylor,et al.  Turbulent gravitational convection from maintained and instantaneous sources , 1956, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[26]  S. Pórarinsson.  The Tephra-Fall from Hekla on March 29th 1947 , 1954 .