Term
| Most present day volcanoes in the volcanic arc are younger than? (how many years) |
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Definition
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| The most recent eruption of a volcano within the Cascades are occurred in? (what year) |
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The Mount St. Helens eruption had a VEI of? (number)
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| The visible cone of Mt. St. Helens prior to May 18, 1980 had formed in the last? (approximately how many years? |
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| What were the first signs of a potential eruption at Mt. St. Helens? |
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| On Sunday, May 18, 1980, Mt. St. Helens erupted explosively. What triggered the eruption? |
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Definition
| A magnitude 5.2 earthquake with a focus located about 1 mile under volcano |
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Term
| The landslide-debris avalanche traveled at speeds of? (kilometers per hour) |
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Definition
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Term
| The landslide-debris avalanche traveled down the North Fork of the Toutle River and filled it to a depth of? (approx. how many meters) |
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| What is the maximum estimated speed of the pyroclastic flow created by the lateral blast? (approx how many kilometers per hour?) |
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Definition
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Term
| The eruption column following the lateral blast climbed to what height? (approx. how many kilometers) |
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Definition
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Term
| The eruption that began on May 18th 1980 was over by? (what day) |
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Definition
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Term
| The May 18 eruption lowered the highest point of the summit of Mt. St. Helens by? (how many meters) |
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Term
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Definition
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Term
the Cascades volcanic arc lies along the leading edge of the ____________ _____________
plate. |
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Definition
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Term
| The Cascades volcanic arc extends from ___________ ___________ in the south, through ____________, and then ___________ before terminating in southern ____________. |
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Definition
| northern California; Oregon; Washington; Canada |
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Term
| Is the Cascades volcanic arc intra-oceanic or continental-margin? |
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Definition
continental-margin
(hint: its not on the ocean so it cannot be intra-oceanic) |
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Term
| list at least 2 prominent volcanoes that lie within the Cascades arc from each of the following states: California, Oregon, Washington |
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Definition
CA : Lassen Peak, Mt. Shasta
OR : Crater Lake, Mt. Hood
WA : Mt. St. Helens, Mt. Rainer |
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Term
| What kind of event is produced when hot magma encounters ground water? |
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Definition
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Term
| Volcanic tremors are different from the distinct short jolts characteristic of earthquakes along major faults. They are described as _____________ rhythmic shaking of the land surface. |
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Definition
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Term
| The volcanic tremors that occured on March 31, 1980 were interpreted to signal what? |
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Definition
| The movement of magmaor gases beneath the volcano |
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Term
| About 10,000 earthquakes were recorded through mid-way with the greatest concentration occouring in a small area less thatn 2.57 km beneath a bulge on the north flank of Mt. St. Helens. in fact, the bulge near the summit was more than 137 meters (450 feet) higher than it was in the summer of 1979 and was growing horizontallly in a northward direction at a rate of 1.5 meters/ day (5 fee/day). in addition to the growing bulge, new cracks and fractures were also evident along the north flank. how was all of this activity interpreted? |
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Definition
| It was interpreted to signify that magma was being forced into a sub-volcanic chamber locate dbeneath the growing bulge |
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Term
| The collapse of the north flank of mt. st. Helens unloaded the summit and triggered the expansion of high temperature-high pressure steam trapped in voids and cracks, and gases dissolved in the dacitiv magma that had produced the northward bulge. the result of this sudden and catastrophic expansion of steam and magmatic gases was a northward-directed . |
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Definition
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Term
| The collapse of the north flank of the volcanoe produced a landslide-debris avalanche. How is this avalanche ranked in history? |
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Definition
| The largest recorded in historic time. |
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Term
| The northward directed lateral blast formed a that devastated a fanshaped sector some 597.7 square kilometers in area. |
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Definition
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Term
| Though the pyroclastic flow created by the lateral blast occurred seconds after the landslide debris avalanche did it have enough speed to overtake the avalanche? |
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Definition
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Term
| The devastations form the lateral blast reached as far as _____ kilometers form the volcanoe. |
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Definition
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Term
| The area affected by the lartyeral blast can be subdivided into three roughly consentric areas. what are theses three consentric areas called? |
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Definition
| Direct Blast Zone, Channelized blast zone, seared zone. |
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Term
| was there anything left standing within the direct blast zone? |
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Definition
| no, everything that was standing was carried away or vaporized by the pyroclastic flow |
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Term
| What happened to trees within the channelized blast zone? |
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Definition
| they were all knocked down |
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Term
| what happened to the trees in the seared zone? |
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Definition
| They were singed brown by the hot gases of the pyroclastic |
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Term
| was lightening produced during the eruption? If so, then what were its effects? |
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Definition
| yes, vegetation and trees were set fire |
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Term
| following the lateral blast, what process produced pyroclastic flows as the eruption column climbed to ~19.3? |
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Definition
| Parts of the eruption column collapsed, generating several pyroclastic flows that moved down the flanks of the volcano |
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Term
| minutes after the may18 eruption destructive lahars were produced. What specific events initiated the development of these lahars? |
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Definition
| pyroclastic flows traveling over the glacier and snowfields near the summit of Mt. St. Helens |
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Term
| the early lahars likely were the products of wet or dry rock avalanches |
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Definition
| early lahars were all produced by wet rock avalanches |
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Term
the lahar was the greatest volume entered and flowed down the North or South Fork Toutle river?
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Definition
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Term
| in the 2 weeks following the may 18th eruption, how far had ash spread |
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Definition
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Term
| how many lives were lost due to the may 18, 1980 eruption of Mt. St. Helens? |
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Definition
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Term
Did the landslide-debris avalanche have enough momentum to travel up and over a ridge
~350 meters high? |
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Definition
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