NICARAGUANICARAGUA’S’S CERROCERRO NEGRONEGRO STRASTRATOVTOVOLCANOOLCANO —— HOW DID IT BLOW ITS TOP??? 1) A stratovolcano or composite volcano 6) Large cloud of pyroclastic debris, is built of alternating layers of lava Match the explanations with the numbers on the volcano and find out. steam, and other vapors erupted and pyroclastic (ash or ejected de- from Cerro Negro. The larger, bris) deposits. These deposits accu- heavier fragments fall back on the mulate around the central vent in a cone while the smaller, lighter ash cone-shaped pile. Lava may flow from 6 fragments are carried great dis- fissures (fractures or cracks) radi- tances before they settle. ating from the central vent, whereas the multi-sized pyroclastics are B 7) A smaller cloud of darker material ejected from the main vent. 9 indicates that a localized eruption L has just occurred. 2) Steam and other vapors rising from 10 the large volcanic blocks erupted 8 from the main crater recently. Com- ) Cloud of vapors from the volcano is mostly steam and ash, but also con- pare with the older, cooler volcanic 8 tains chlorine, fluorine, sulfur, and blocks at the ends of the tracks or L 5 their acids. furrows that run down the slope of 5 the main cone. These tracks or fur- 5 9 rows were plowed by the rolling 7 9) Shadow cast by the ash and vapor blocks. Some house-size blocks now 5 cloud from the volcano (6) carried lie loosely at the bottom of the 5 by turbulent hot gasses and winds. slope. 4 When the volcanic ash settles, the 2 pyroclastic deposit that forms is 9 called an ash fall. 3) The crater of a dormant parasitic 5 vent occurs on the side of the larger cone that is subsidiary to it. The 10) A dormant volcanic cone is old parasitic and main craters may have 2 enough to have developed a soil pro- a common source of magma. file and luxurious vegetation on its slopes. The crater rim has visible breach at (B) where lava poured 4) Erupting parasitic vent, possibly a smaller stratovolcano in an earlier from the cone. The lava flow turned 1 at the base of the cone and formed stage of development than the main levees (L) at the sides of the flow. cone. 5 3 Cerro Negro, Nicaragua. December 4, 5) Contacts between lava flows that 1968. Cerro Negro erupted again in emanated from the parasitic vent 1972. Photo by R.L. Williams, cour- (4). These flows are small enough to tesy of Dr. Ian Campbell. be easily distinguished. The larger lava flows from Cerro Negro (left 5 5 and right foreground) coalesce mak- ing it difficult to distinguish indi- vidual flows. 1 CALIFORNIA GEOLOGY MAY/JUNE 2001 CALIFORNIA GEOLOGY MAY/JUNE 2001 27.