Volcanology methods
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.
Geology in the field
Dr Darren Gravley takes us into the field and describes the work of a geologist. Looking at a rocky outcrop. he describes what geologists are looking for and what the rocks can tell them about volcanic eruptions.
Fieldwork methods can include:
surveying
collecting rock samples
drilling core samples
seismic monitoring
gas monitoring
ground deformation monitoring.
Laboratory techniques can include:
electron microprobe
radiocarbon dating
potassium-argon dating.
Surveying
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.
Dr Phil Shane at The University of Auckland. He looks at rock core samples – drilled sections from the bottom of lakes and swamps that preserve the geological history.
Seismic monitoring
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.
Seismometer
Dr Jan Lindsay with an underground seismometer. Seismometers are devices that are placed around the earth to ‘listen’ for seismic waves, which are associated with tectonic plate movement.
Gas monitoring
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 sulfur 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.
Measuring volcanic changes
GPS instruments pick up millimetre-sized changes in the shape of a volcano. Swelling can sometimes be an early sign of volcanic unrest.
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.
Electron microprobe
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
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.
Preparing a volcanic sample
Dr Jan Lindsay prepares a volcanic sample for carbon dating. Dr Lindsay is a volcanologist in the School of Environmental Science at The University of Auckland.
Potassium-argon dating
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.
Measuring magma
Dr Phil Shane describes how geologists study magma. How do you know where it came from? How do you find out when it formed? What does it tell you about volcanoes today?
Submarine volcanoes
The devastating Hunga Tonga–Hunga Haʻapa volcanic eruption in January 2022 was a wake-up call to pay more attention to the threat of submarine volcanic eruptions. It is difficult, expensive and time-consuming to study submarine volcanoes, but we now know that monitoring needs to be improved. Submarine volcanoes are not only dangerous due to the magma and ash of an explosion but they also have the potential to cause a tsunami. A team from the Tongan Geological Services and the University of Auckland used a multibeam sonar mapping system to find out more about the Hunga eruption, explore their work further here.
Mapping an underwater volcano
A multi-beam sonar mapping system was used by Tongan Geological Services and the University of Auckland to precisely measure the shape of the Hunga Tonga-Hunga Ha’apai volcano.
Work is underway on improving volcanic monitoring around Tonga using onshore and offshore seismic sensors along with infrasound sensors and a range of satellite observation tools.
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.
Related content
Types of volcanoes and Types of volcanic rock introduce some of the key ideas and concepts in understanding more about volcanoes.
Find out how scientists used volcanic carbon dioxide in groundwater to more accurately date the Taupō eruption.
Find out more about these scientists:
Associate Professor Darren Gravley – researches the accumulation of large magma bodies, the processes of caldera eruptions and pyroclastic flows, and the geologic context for geothermal systems.
Professor Jan Lindsay – works on volcanic hazard and risk (with a focus on Auckland)
Emeritus Professor Richard Price – studies volcanoes and their products, granites and related rocks and the tectonic history and magmatic systems
Associate Professor Phil Shane – specialises in examing rock core samples.
Read how scientists are using cosmogenic surface exposure dating, an absolute dating method in A clock in the rocks – cosmic rays and Earth science.
Activity idea
In Making a core sample students use (or observe the teacher using) a small coring tool to make a core sample from some available waste ground and examine the resulting sample for features such as particle size, colour variation and layering.
Useful links
Listen to this Radio NZ Our Changing World programme, Volcanic hazard alert system, to find out more about Massey University volcanic eruption simulator.
