A seismometer is an instrument that responds to ground noises and shaking such as caused by quakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The output of such a device—formerly recorded on paper or film, now recorded and processed digitally—is a seismogram. Such data is used to locate and characterize earthquakes, and to study the internal structure of Earth.
Kinemetric seismograph.
Basic horizontal-motion seismograph. The inertia of the round weight tends to hold the pen still while the base moves back and forth.
Replica of Zhang Heng's seismoscope Houfeng Didong Yi
Milne horizontal pendulum seismometer. One of the Important Cultural Properties of Japan. Exhibit in the National Museum of Nature and Science, Tokyo, Japan.
Types of volcanic eruptions
Several types of volcanic eruptions—during which material is expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.
Some of the eruptive structures formed during volcanic activity (counterclockwise): a Plinian eruption column, Hawaiian pahoehoe flows, and a lava arc from a Strombolian eruption
Ropey pahoehoe lava from Kilauea, Hawaiʻi
An example of the lava arcs formed during Strombolian activity. This image is of Stromboli itself.
Tavurvur in Papua New Guinea erupting
