VO L2: What Threats Do Volcanoes Pose? Flashcards
Why has the rate at which humans have been killed by volcanic eruptions greatly increased since 1800?
as world population increases, more people are living closer to active volcanoes
What temperature do mafic lava flows erupt at?
1200 - 1400 degrees C
How do mafic lava flows flow?
Low viscosity, so they can flow and spread laterally out of a stream canyon onto a valley floor.
What kind of lava flow is non explosive?
Mafic lava flows.
Hazard of mafic flows?
Infrastructure damage (roads and buildings are easily overrun and incinerated). Most people can run out of the way or avoid it.
From where does lava flow on shield volcanoes? How does it flow?
from fissures. They erupt from long periods of time, and cover very large areas.
How many shield volcanoes on Hawaii? Youngest to oldest?
- Kilauea, Mauna Loa, Mauna Kea, Hualalai and Kohala
What are fire fountains? How are fire fountains created?
Small explosive eruptions, created from the excessive gas that basaltic lava sometimes contains. They may come together and reform a lava flow as they fall back to the ground.
What is tephra?
pyroclastic material (synonym)
What is scoria?
mafic pyroclasts
What are the smallest pyroclasts?
Ash particles, <2mm diameter.
How are ash particles formed?
form from fragmentation of a frothy magma, when the PRESSURE within the gas bubbles EXCEEDS the strength of the viscous magma
Describe the step-by-step process of how the gas bubbles form.
Gas bubbles form in a high-silica magma but do not pop because of the high viscosity. Therefore, the pressure in each bubble increases as the magma makes it way towards the surface.
The bubbles expand until they are almost touching. At this point the magma is frothy, as only thin walls of silicate melt are present in between adjacent bubbles.
BOOM! The gas pressure in the bubbles exceeds the strength of the thin walls of silicate melt, causing explosive fragmentation, and triangular glass shards called ash rise into the atmosphere in an eruption column. Some larger fragments (see definitions below) are left from incomplete fragmentation of the gas-rich magma.
In what kind of magma do gas bubbles form?
high-silica magma
Why don’t gas bubbles pop while in the magma?
Because of the high viscosity. The pressure in each bubble increases as the magma makes its way towards the surface.
How is ash deposited in large explosive eruptions?
Ash falls downwind of volcano. Ash can rise >40 km altitude, where fine ash particles are picked up by global winds and circulated around the world.
How can ash contribute to global cooling?
Ash injected into the stratosphere can contribute to a lower amount of solar radiation reaching Earth’s surface. Lower amount of solar radiation = cooler temperatures
What is so bad about ash for humans?
Ash can choke vehicle and airplane engines, aggravate respiratory ailments, bury homes and other structures and/or cause their collapse, and cover valuable agricultural land, thereby decreasing the food supply and leading to famine.
What are lapilli?
pyroclasts in the 2 – 64 mm range, arger than ash particles. These are associated with large eruption columns and are mostly fragments of vesicular felsic rock called pumice. Lapilli-sized pumice fragments fall out of an eruption column and blanket surrounding areas, forming a pumice fall deposit.
What are the largest pyroclasts?
Bombs and blocks (> 64 mm in diameter). These are explosively ejected during an eruption as ballistic projectiles, most of which land near the volcanic vent.
