Grindavík Lava Flow EarthCache
Hidden : 8/8/2024
Difficulty:
2 out of 5
Terrain:
1 out of 5

Size: Size: other (other)

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Geocache Description:


Important Update


I have been informed that the posted coordinates for this Earth Cache are now off limits. Feel free to complete this Earth Cache from any permitted and safely accessible location at the Grindavík Lava Flow.

A Recent Lava Flow


This Earth Cache provides a unique opportunity to observe a very fresh (as of this posting, only a few months old) lava flow. The logging tasks can be completed from a paved parking area. Obey the warning signs and do not walk out onto the lava flow. Should you encounter a "soft" spot and fall through or release a pocket of gas you could be seriously injured or killed. Stay on the pavement!

In where else but Iceland can you have both the "Wheelchair Accessible" and "Dangerous Area" attributes on the same cache?

Your logging tasks will be to identify the type of lava flow (pāhoehoe or ‘a‘ā, as described below), note the color of the lava, and to take a photo at this location. All of this is accomplished from the safety of the paved parking area.

Grindavik Volcano Eruption


In May 2024, a volcano in southwestern Iceland erupted for the fifth time since December 2023, threatening the coastal town of Grindavík and the Blue Lagoon geothermal spa. The lava covered roads and required evacuations at the Blue Lagoon. Defensive walls were built along the northwest side of town to divert the lava away from buildings. However, the town has since been abandoned.



As of the time of this posting, the main road is (obviously) closed and an alternate route has been constructed to the Blue Lagoon. The new "end of the road" is open to parking and viewing the lava flow. No permission is required to park here, and there is no parking fee.



Types of Lava Flow


Lava flows are categorized into two types.

  • Pāhoehoe – Lava flows with smooth, billowy, or ropy surfaces
  • ‘A‘ā – Lava flows with rough, jagged, or clinkery surfaces
These Hawaiian descriptions of lava were introduced by geologist Clarence Dutton in 1882. Roughly translated, pāhoehoe means "smooth unbroken lava" and ‘a‘ā means "rough stony lava."

Pāhoehoe and ‘a‘ā lava flows do not differ in composition in any significant way, but there are important differences between them in terms of temperature, viscosity, and other characteristics.

Pāhoehoe

ʻA‘ā

Surface Description

Smooth, ropy

Rough, clinkery

Viscosity

Low

High

Velocity

Low

High

Eruption Rate

Low

High

Thickness

Thin

Thick

Distance from Vent

Less

Greater

The viscosity of the lava flow is the primary factor in whether the result is pāhoehoe or ‘a‘ā lava. If the flow has low viscocity and flows slowly and smoothly, it tends to cool with a relatively smooth surface. If the flow has high viscocity and flows rapidly, it cools unevenly and the flow is torn apart by shear strain, forming a rough breccia at the top of the flow.

The Color of Lava


Lava can be many different colors. Lava that cools relatively slowly is often grey in color, as in common surface rocks which might have taken thousands of years to cool. Roads cut through older lava flows in Iceland expose their medium grey internal color. Lava that cools quickly, especially the outer layers of a flow, are primarily composed of glass particles and tiny mafic minerals that give it its dark color.

Logging Requirements




Obey The Warning Signs!

Send your answers to the following questions to the CO:

(1) Based on your observations, is this lava flow pāhoehoe or ‘a‘ā lava?

(2) What is the dominant color of this lava flow, and what does this say about the way this lava cooled?

As per current Earth Cache logging requirements, please post a photo that includes you, your group, or something recognizable that documents that you were present at the site.

References


Lava (Wikipedia)
Lava Flow Forms (National Park Service)
Blue Lagoon evacuated after volcanic eruption near Grindavík (Sky News)

Additional Hints (No hints available.)



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