Explosive volcanic activity is usually associated with intermediate and silicic lavas (e.g.,…

Explosive volcanic activity is usually associated with intermediate and silicic lavas (e.g.,…

Explosive volcanic activity is usually associated with intermediate and silicic lavas (e.g., andesitic to rhyolitic). As shown in Table 1, these lavas solidify into volcanic rocks with 52%-65% and >65% silica (SiO2), respectively. Consequently, geologists measure the amount of silica in volcanic rocks to better understand the threat of explosive volcanic activity. In this lab, you will use the amount of silica in volcanic rocks to help you evaluate the threat of explosive volcanic activity at five sites (A through E) in Costa Rica (Figure 1). Questions: 4) Use Table 1 to assign a composition to each rock sample in Table 2. In the COMPOSITION column of Table 2, write “U” for ultramafic, “M” for mafic and so on. (3 points) 5) At which site are all samples intermediate? (1.5 points) 6) At which site are all samples mafic? (1.5 points) 7) Based on your answers to #5 and #6 above, at which site is the potential for explosive volcanic activity least, and why? (Assume the samples are representative of the geology at the site.) (1.5 points) 8) Which site(s) yielded rocks indicating at least some potential for explosive volcanic activity? (1.5 points) 9) Extremely explosive volcanic activity can form an ignimbrite – a kind of silicic flow. Knowing that, is the volcanic hazard greatest in northern or southern Costa Rica? (1 point)
Apr 06 2022 12:56 PM