A violin can be used, but its effectiveness is limited.
seismograph is one instrument that could measure earthquakes and volcanoes etc but seismograph is many times use at earthquake!
the instrument that the used was an intelligent brain
A compass is used to find your location in a forest
Graduated cylinder
Pressure gauges.
A scale
volcanoes are used for nothing
This instrument is called pluviometer (a rain gauge). See the link below.
A set of scales
radar
Scales.
Yes, it is not uncommon to find volcanoes at hot spots.