Pyroclastic flows from the May 18, 1980eruption ran out only about 8 km (5 mi) from
thevent.
As they impinged on Johnston Ridge, theywere deflected westward downvalley and
eastwardto Spirit Lake.
During the past 4,000 years:
during which time the volcanos
Lava flows:
are destructive but:
- generally notlife-threatening because:
- they normally advance so slowly that people can walk or run away from them.
Extremely viscous dacitic lava:
does not flow easily;
it tends to form steep-sided lava domes overvents
Similar explosions could occur
-without warning in the future
- but become progressively less likely with continued cooling of the domes hot interior
-and the subsurface conduit that supplied the magma for dome growth.
Lateral Blasts
A lateral blast is a
Lahars
-they are gravity-controlled flows that are channeled into valleys
-as they move downhill
-they can flow about twice as fast as water in channels of similar depth and slope.
Lahars triggered at Mount St.Helens in 1980 were 3 to 15 m (10 to 50 ft) d
It updates previous assessment:
taking into account both recent experience aterupting:
volcanoes
topographic
hydrologic
geologic changes initiated at Mount St. Helensby the 1980 eruptions.
These changes include
(1)beheading of the summit, forming a trunca
Explosive Ejection of Ballistic Projectiles
Volcanic explosions:
can impel rock fragments on ballistic trajectories that may be counter oroblique to the
wind direction.
Such events may occur:
either during or independently from an ongoing magmatic eruptio
Neither a large debris avalanche nor a major lateral blast like those of May 18, 1980is
likely now that a deep, open crater has formed.
Sufficient time has elapsed since the lastdome-building eruption in October 1986 for
magmain the conduit beneath the do
Ash suspended in the air from a large eruption can be a major source of aggravation
and hazard:
even hundreds of kilometers (a few hundred miles)downwind from its source
-both during its initialaccumulation and later as fine dry ash is remobilized by wind
(The May 18, 1980 tephra plume rose about 25 km [15 mi] in less than 30 min).
As the energy required to keep them in suspension diminishes:
the particles begin to fall out of the plume under the influence of gravity.
Large fragments:
fall back to earth cl
Addition of a 50 percent safety factor to the 10-km (6-mi) range identified for ballistic
fragments
-from the Sugar bowl blasts suggests that hazard from rock projectiles might extend 15
km (9 mi) northward from the crater
-in laterally directed explosion
What pair of processes make rivers dynamic?
The pair of processes that make rivers dynamic is erosion and deposition are always changing
the river.
Where does it rain?
-Hadley cell circulation
equatorial band have integrated the solar radiation per square
