An extreme wind erosion event of the fresh Eyjafjallajökull 2010 volcanic ash

Abstract

Volcanic eruptions can generate widespread deposits of ash that are subsequently subjected to erosive forces which causes detrimental effects on ecosystems. We measured wind erosion of the freshly deposited Eyjafjallajökull ash at a field site the first summer after the 2010 eruption. Over 30 wind erosion events occurred (June-October) at wind speeds > 10 m s(-1) in each storm with gusts up to 38.7 m s(-1). Surface transport over one m wide transect (surface to 150 cm height) reached > 11,800 kg m(-1) during the most intense storm event with a rate of 1,440 kg m(-1) hr(-1) for about 6½ hrs. This storm is among the most extreme wind erosion events recorded on Earth. The Eyjafjallajökull wind erosion storms caused dust emissions extending several hundred km from the volcano affecting both air quality and ecosystems showing how wind erosion of freshly deposited ash prolongs impacts of volcanic eruptions.

Figure 1. Hill shade map of Eyjafjallajökull and the surrounding areas showing location of the research site and isopach data indicating the main distribution of the 2010 tephra.

The distance from the crater to the research site is about 12 km. Isopach data from Gudmundsson et al..

Figure 2. Sediment transport measured with automated saltation sensor during the storm September 14 (13:46 hr) – September 15 (23:08); 2010.

The storm is divided into 7 episodes labelled I-VII on the graph with the most intense sediment transport during episode V.

Figure 3. Wind erosion of Eyjafjallajökull volcanic ash presented as saltation pulse counts at 10 cm height.

Figure 3A shows data for the entire storm period while Figure 3B shows saltation as a function of maximum wind speed per minute for the most intense episode of the storm. Note different scale for the x-axis. Evidence of grain saturation is evident at maximum wind speeds above 28 m s⁻¹.

Figure 4. Cumulative grain size for materials trapped by the BSNE samplers during the storm.

The difference in grain size is notably small.

Figure 5. Instrumentation at site.

A Senist saltation sensor (white) together with equipment to measure wind speed and relative humidity. The instruments are solar powered and data is stored in a datalogger hosed in the white box, and can be accessed by a telephone link. BSNE samplers mounted on a pole in the background. The photo is taken after the occurrence of one major storm and ash has eroded from exposed sites while depressions have accumulated ash (photo: JT, June 23, 2010).

Figure 6. A pole with five BSNE samplers placed at 10, 30, 60, 90, and 120 cm height.

The opening is always directed upwind (photo: JT).

Figure 7. Height distribution of materials collected at 10, 30, 60, 80, and 120 cm height during three storms prior to the main storm discussed in the paper.

Materials collected in the 10 cm sampler is given the value of 1, others proportional to the amount in the 10 cm trap.