Published on October 9, 2007
Temporal Trends In Lava Dome Extrusion At Santiaguito 1922-00: Temporal Trends In Lava Dome Extrusion At Santiaguito 1922-00 Andrew J.L. Harris, William I. Rose, Luke P. Flynn Presentation by: Jason Evans Preface : Preface The October 1902 eruption of Santa Ana (Guatemala) yielded a 0.5 km3 in the previously symmetrical 20km3 crater Eruption emitted 8.5km3 of dense dacite Post eruption period yielded geyser activity and weak ash emission until 1922 In 1922, lava began extruding in the 1902 crater and continued until 1984 creating Santiaguito dome complex Santiaguito formed by 22 distinct flows (0.9 km3) Effects of Santiaguito: Effects of Santiaguito El Palmar was abandoned and destroyed by lahars beginning in 1983 Increased rate of intrusion will increase possibility of PDCs and supply of volcanogenic material to river basins and catchments Block and ash flows of 11km long, regular ash emissions, incandescent rock falls, and black lava flows have characterized the Santiaguito process since 1922 Larger ash eruptions to 4km high and dome collapses have also been observed The Good News and the Bad: The Good News and the Bad Bad Monsoonal weather patterns that create problems with visual observations as clouds cover the area often As of January 2000 no geophysical monitoring equipment was available to the observatory staff Only a few days per year are available for comparisons Good Landsat 4, 5 and 7 image Santiaguito 2 times every 16 days (on a borderline range of images) 29 images from 1987-2000 with 18 clear (cloud free) days Clouds don’t move in until after around 10:30 am as the ground heats enough to create clouds Background/Geography: Background/Geography Rose has proclaimed the Caliente vent as the principal/central vent – exhibiting the highest fumarolic and geyser activity prior to 1922 with persisting gas, pyroclastic and lava emissions since 1922 La Mitad vent is around 700 m west of Caliente El Monje (west of La Mitad??) El Brujo vent is about 1.5km West of Caliente 6 Cycles: 6 Cycles La Mitad 700m West of Caliente El Monje West, undefined location El Brujo 1.5 km West Landsat Imagery 1986-00: Landsat Imagery 1986-00 30 m shortwave thermal bands and 120 m longwave thermal bands find active lavas easily… by adapting these to contour plots of Santiaguito, mapping of block flows can accomplished Between 1986-89 and 97-00 block flows greater than 1.5 km were found They are separated from 1990-97 flows less than 1.5 km Estimations of Activity: Estimations of Activity Useful Equations I (direct from text): Useful Equations I (direct from text) Extrusion rate- R5, R6, and R7 are the at-satellite radiances corrected for atmospheric, surface emissivity and reflection effects, in bands 5, 6, and 7 Ll is the Planck function for TM band l (l=5, 6, or 7) pb is the pixel portion occupied by ambient ground surrounding the sub-pixel lava body Tb is the temperature of the ambientground Th, Tc, p, and Alava are obtained using emitted thermal radiation in TM bands Crustal Temps range from 90-255 deg C, with s.d of 64 and mean of 164… this is close to field obs (29-303, m=120, sd 67 Correction Factor for different sized pixels THIS MEANS NO PIXEL COUNTING OF LAVA!!! Good/Bad- does it work?: Good/Bad- does it work? Conclusions: Conclusions It was found that exogenous growth occurred when the magma pressure was greater than tensile rock strength Block flows versus lava dome building depend underlying slope and yield strength 1925-58 was a transitional time period given by conflicting results of critical failure thickness and dome thickness… later rheological and pressurization conditions favored block flow Pressurization was key in temporal trends, as pressurization cause higher rates BOTTOM LINE- Landsat Imagery is a great tool for estimation and confirmed just about every aspect of Santiaguito eruptions within a reasonable error.