Answer:
The type of equipment and techniques we use to study volcanoes
depends on the particular volcano topic we are investigating and
on the experiment we are conducting. When specialized
instruments are not available for a special study or for
monitoring a specific type of activity, we design and build our
own.
For reconstructing a volcano's eruptive history so that we can
identify the type of activity most likely to occur in the future
as well as the areas around a volcano that are likely to be
effected by future eruptions, we use many geologic mapping and
dating strategies. These include:
Identifying rock outcrops, formations, and features on the
ground and identifying their exact location on detailed aerial
photographs and topographic maps or in computerized geographic
information systems (GIS).
Collecting dozens to hundreds of volcanic rock and ash samples
from sites located on or near the volcano and also tens of
kilometers downwind or downstream, and then using laboratory
techniques for determining their chemistry and mineral
compositions.
Determining the ages of as many rock deposits formed by past
activity of the volcano by using several common methods.
Carbon-14 dating when a volcanic deposit either incorporated or
came to rest on top of vegetation or organic-rich soil and
sufficient carbon-bearing material can be found. It's based on
the fact that living trees and other organic matter contain
small amounts of carbon's radioactive isotope (atomic weight of
14). When a tree is killed by a volcanic deposit, its
radioactive carbon begins to decrease by radioactive decay at a
known rate. By measuring the 14C/12C ratio in the wood sample,
its age can be calculated. This technique can adequately date
deposits that are as old as about 50,000 years, and each date
may have an error range of between a few tens to several hundred
years. The most common technique for dating recent volcanic
deposits, only a few scientific laboratories in the United
States can perform the carbon analysis.
Tree-ring dating
when a volcanic deposit caused an unusual growth pattern of
annual rings among trees growing at the time the deposits were
emplaced. This technique can sometimes date deposits to an
actual calendar year or to within a few years when used to on
deposits of the past few hundred years.
Paleomagnetism in some volcanic areas where scientists have
determined the yearly changes in the position of the Earth's
magnetic pole over the past several hundreds or thousands of
years and when the Earth's magnetic direction is preserved in
volcanic rocks (usually lava flows and individual large rocks in
pyroclastic flows); this technique usually yields ages with a
range of between a few tens and several hundred years.
Representing the types and ages of volcanic rock deposits and/or
identifying volcanic hazard areas around the volcano on a paper
map or computerized geographic information system.
