D - Volcanoes Flashcards
What are the main characteristics of shield volcanoes?
Shield volcanoes have gently sloping sides, a shallow crater, and a large circumference. They form from very hot, runny basaltic lava that can flow over great distances.
Why are shield volcanoes not typically explosive?
Because their basaltic lava is very hot and fluid, allowing gases to escape easily and preventing the buildup of explosive pressure.
How do composite (strato) volcanoes form?
They form from alternating eruptions of fragmental material (pyroclasts) and lava outflows, creating layers that build a tall, cone-shaped mountain.
Give an example of a composite volcano.
Mount Etna in Italy is a composite volcano (others include Vesuvius, Chimborazo, and Popacatepetl).
What slope angles characterize composite volcanoes?
They typically have slopes of about 30° near the summit and 5° near the base.
What are cinder volcanoes composed of?
They are formed from fragments of solid material (cinders and ash) that accumulate around a vent to form a steep conical hill.
How high can cinder volcanoes typically reach?
Most are relatively small (up to about 300 m), though some exceptions (e.g., Volcano Du Fuego in Guatemala at 3,350 m) are taller.
How does silica content affect lava eruptions?
Higher silica makes lava more viscous, leading to more explosive eruptions (as in Japan or the Philippines), while lower silica (Iceland, Hawaii) allows runny, continuous flows.
What is characteristic of Icelandic lava eruptions?
They feature persistent fissure eruptions of basaltic lava, forming large horizontal plains and typically minimal pyroclastic activity.
How do Hawaiian eruptions differ from Icelandic eruptions?
Hawaiian eruptions involve a central vent rather than a fissure. They can have some pyroclastic activity but mainly produce runny basaltic lava with easily escaping gases.
What are Strombolian eruptions known for?
They are explosive eruptions that produce pyroclastic rock and are often marked by a white cloud of steam emitted from the crater.
What triggers Vulcanian eruptions?
They occur when trapped gases in viscous magma build enough pressure to blow off the solidified lava crust, resulting in violent eruptions.
Name two primary hazards associated with volcanic eruptions.
Lava flows and pyroclastic flows are primary hazards, along with ash fallout and gas emissions.
What are lahars and why do they form?
Lahars are volcanic mudflows formed when volcanic ash mixes with rainwater or melting snow, creating fast-moving, cement-like flows.
How can landslides be related to volcanic activity?
Debris avalanches often occur around the same time as eruptions and may destabilize slopes, potentially aiding or triggering an eruption.
