Scientists use a range of different methods to learn more about volcanoes. A volcanologist may start by conducting fieldwork, collecting rocks and samples, and then move into the lab to undertake detailed analysis. The combination of data from all this research will be combined to form a detailed picture of the volcano being studied.
Fieldwork methods can include:
- collecting rock samples
- drilling core samples
- seismic monitoring
- gas monitoring
- ground deformation monitoring.
Laboratory techniques can include:
- electron microprobe
- radiocarbon dating
- potassium-argon dating.
A volcanologist’s first job is to stop and look around. Nothing is collected or touched until they have made a full survey, which could include drawing the area. This provides a record of rock layers, the general landscape and where samples were collected. Volcanologists often use a notebook to make sketches and record data when they are in the field, and they also use laptop computers and digital cameras.
Collecting rock samples
The volcanologist’s standard tool is a rock hammer, which is used to chip off and collect samples from rocky outcrops. Volcanologists are looking for igneous rocks so that they can learn more about where these rocks have come from and whether they were formed during a volcanic eruption. These samples are analysed visually in the field and back in the laboratory to determine exactly what they are, what they are made of and how they may have been formed.
Drilling core samples
As different events happen – volcanic eruptions, rain or sediments settling – layers of different rock can accumulate. Geologists can use this to tell more about when things happened and to date different events. Sometimes the rock the volcanologist is interested isn’t exposed, so they may need to drill deeper for samples. Hollow steel pipes, 2 metres long, are driven into the ground using large weights. The pipe fills with earth and rocks – this is called a ‘core sample’. Each section of the core sample is recorded and numbered so scientists can reconstruct the layers in the right order back in the laboratory. A sample might be made up of different layers of ash (tephra), igneous rock and sedimentary rock, and there might be fossils or other material buried in the layers that offer further clues.
As magma rises through the crust towards the Earth’s surface, it can cause the crust to move and bulge. This movement or deformation can be detected by using seismographs, which measure the Earth’s movement, so they are an important tool for studying whether a volcano might erupt in the near future.
If volcanologists suspect that a volcano is active or may be about to erupt, they can monitor the gases that are being released from the vent. These gases include water vapourcarbon dioxide and sulphur dioxide. As the magma rises to the surface, the composition of the gases being emitted can change, and volcanologists can use this information to predict how soon the volcano may erupt.
Ground deformation monitoring
Scientists use satellites and GPS technology to see whether the ground is moving or deforming. This can be really important in a volcanic field such as Auckland where no two volcanoes occur in the same place. As magma rises from the field under the city, scientists may be able to see the bulges that are created in the Earth’s surface.
Back in the laboratory, an electron microprobe allows scientists to measure the composition of small rock fragments that have been collected in the field – what minerals and crystals are present and how old they are. These measurements provide clues about the chemical composition of the volcanic material and allow scientists to identify the type of volcanic material and some information about the processes that helped to form them.
Radiocarbon dating in volcanology is an indirect method of analysis as it cannot be used to date the rocks itself. Instead, it is commonly used to date fossils that are located in the rocks. Radiocarbon dating relies on the predictable decay of carbon atoms (from something that was once living) over time. Rocks contain no carbon, but volcanic explosions often trap material such as trees and leaves in the falling ash layer. These can look like chunks of charcoal in amongst the rock so it takes a trained eye to spot them. Radiocarbon dating can also be used to date the layers either side of the volcanic rock, such as sedimentary material that contains organic deposits.
Potassium-argon (K-Ar) dating is based on the same principle as carbon decay and can be used to date rocks directly. Volcanologists can measure the decay of potassium (K) to argon (Ar) that occurs over very long periods of time. One problem is that basalt rocks (the type commonly found in Auckland) are generally very low in potassium, so this technique is not always reliable.
Putting the story together
With the combined information, volcanologists can start to develop an explanation. The clues give information about when a volcano erupted, what type of eruption it was and how much material was produced. Sometimes, this information is not complete and some of the clues may be missing, but over time, as more information is added, the explanation slowly becomes more convincing.
Nature of science
Scientists try to combine a number of research techniques to find the answers to the questions that they are asking.
Find out how scientists used volcanic carbon dioxide in groundwater to more accurately date the Taupō eruption.
Listen to this Radio NZ Our Changing World programme, Volcanic hazard alert system, to find out more about Massey University volcanic eruption simulator.