Hekla                       ₁ 

Current Monitoring

Because Hekla is such an active volcano, as are many other volcanoes in Iceland, monitoring for threats is taken very seriously.  There are several organizations dedicated to monitoring the area around Hekla for any changes that might indicate volcanic activity.  These changes are taken very seriously, because there is usually very little warning before an eruption at Hekla.  These changes include seismic activity, specifically volcanic tremors, strain in the bedrock and ground deformation.  Volcanic tremors are earthquakes that have a low frequency that represent the movement of a liquid (magma) underground.  These earthquakes generally have smaller magnitudes and take a while to taper off (they have longer codas). 

The Physics Department of the Icelandic Meteorological Office closely monitors seismic activity on the entire island.  There are stations set up near the volcanoes to monitor any changes. 

This map shows the location of seismic stations across the country.  I have placed a green star at the location of Hekla.  ³⁰

The Physics Department of the Icelandic Meteorological Office also provides very up-to-date information about earthquakes that have taken place within the last 24 hours.  Monitoring the seismic activity and having a lot of background information provides data that is useful for comparisons.  Geologists and Volcanologists have to have some idea of what the background tectonic noise is to be able to know when something significant is happening.  However, Soosalu writes, “Volcanic tremor often begins prior to the actual surface outbreak of an eruption and may extend beyond the duration of surface activity.  This was not the case at Hekla where the tremor started at the same time as the eruption, and also stopped simultaneously with the eruptive activity.  Thus, the tremor observations cannot be used for predicting the Hekla eruptions” (p. 575). ²⁸

This map shows earthquakes in Iceland from April 23, 2008 until April 25, 2008.  The circles represent the location of the earthquakes.  The color of the circles represent the time that has elapsed since the earthquake has occurred.  Red circles show the most recent earthquakes, while the blue circles show earthquakes that happened more than 24 hours ago.

This map shows the location of seismic activity across the country.  I have placed a green star at the location of Hekla. ³¹

Because seismicity is not as helpful at Hekla as it is at other volcanoes, other factors, like strain and ground deformation are also used.  Ground deformation uses GPS monitoring stations to determine changes in the crust due to plate movement,  volcanic activity and earthquakes.  Normally, preceding an eruption, the crust swells with magma.  After the eruption (or during the eruption), the crust deflates again. 

              This map shows the location of all of the GPS monitoring stations in Iceland.  The station labeled ISAK is the closest to Mt. Hekla.  32

The last method for monitoring Hekla’s activities includes measuring strain on the surrounding bedrock.  To detect strain, boreholes are drilled to measure any changes in the bedrock, including contractions, extensions and volume changes.  These changes can indicate the opening and expansion of a conduit and the time when the conduit reaches the surface. ³³  Agust Gudmundsson writes on the importance of stress, “Similarly, the tensile stress concentration at Hekla must have contributed to its unusually frequent eruptions in the past three decades,” (p. 191).²⁷  If stress is contributing to the eruptions at Hekla, it is important to monitor stress to monitor the current state of the volcano. 

This map shows the location of the strain meters in Iceland.³³