GEO quiz 3

In contrast to basaltic lavas, felsic lavas are so vicous that they can just barely flow. They ofetn produce a _______, a rounded, steep sided mass of rock.

When a volcano emits lava as well as pyroclasts, alternating lava flows and beds of pyroclasts build a concave-shaped composite volcano, or _____ These are common above subduction zones. Mount Rainier in Washington State is an example.

If the lava is basaltic, it flows easily and spreads widely. If flows are copious and frequent,
they create a broad ____________ two or more kilometers high and many tens of kilometers in circumference. These are the largest volcanoes. Mauna Loa is a classic example.

When volcanic vents discharge pyroclasts, the solid fragments can build up to create

are particularly spectacular and often devastating forms of eruptions which occur when hot ash, dust, and gases are ejected in a glowing cloud that rolls downhill at high speeds buoyed up by the hot gases.

Among the most dangerous volcanic events are the torrential mudflows of wet volcanic debris called

When hot matter from the deep interior escapes explosively, the vent and the feeder channel below it are often left filled with volcanic breccias as the eruption wanes. The resulting structure is called a

result when a violent eruption empties a volcano’s magma chamber, which then cannot support the overlying rock. It collapses, leaving a large, steep-walled basin.

rather than forming a shield volcano as they do when the eruption is confined to a central vent.

The largest eruptions do not come from a central volcano, but through large, nearly cracks in the Earth’s surface called ________. These are sometimes tens of kilometers long.

The ________ is the geographic point on the Earth’s surface directly above the focus.

In 1910, a geologist who investigated the 1906 San Francisco earthquake, Henry Fielding Reid of John Hopkins University, advanced the _________ to explain why earthquakes occur.

Defined as the product of the area and the average slip above the fault break; the corresponding_________
increases by about one unit for every 10-fold increase in the area of faulting. This intensity scale can be measured more accurately from seismograms, and it can also be determined directly from field measurements of the fault.

This intensity scale assigns a value, given as a Roman numeral from I to XII, to the intensity of shaking and damage observed at a particular site.

To compress this intensity scale, the seismologist took the logarithm of the largest ground motion registered by a seismograph as his measure of earthquake size. On the ______________, two earthquakes at the same distance from a seismograph differ by one magnitude if the size of the ground motions differ by a factor of 10

describes the damage that can be expected over the long term for a specified region, such as a country or state, usually measured in terms of average dollar loss per year.

The foci of these earthquakes are relatively shallow, and most occur on continents.
Many of these _______ occur on old faults that were once parts of
ancient plate boundaries.

The world’s largest and the Earth’s deepest earthquakes occur at

Earthquake activity is even greater along the _______that offset the ridge segments. These earthquakes show strike-slip fault mechanisms- just as one would expect where plates slide past each other in opposite directions.

describes the intensity of seismic shaking and ground disruption that can be expected over the long term at some specified location.