Queens Highway Flow Types EarthCache

The two lava fields at these coordinates show the two main types of flow behaviors of lavas that erupt from the Hawaiian Hot Spot, pahoehoe and 'a'a.

The two coordinates for this EarthCache are along the Queen Kaahumanu Highway which has wide shoulders in both directions. Stopping on either side of the highway is fine; there is no need to get out of you car or turn around to get to the other side of the highway.

Lava on the Big Island is almost exclusively basaltic. The most common basalt is olivine basalt which is made up of labradorite and pyroxene with typically microscopic grains of magnetite and ilmentie. The olivine in in this basalt does grow into larger brownish-green crystals that can be seen. In one place on the island the olivine has created a green sand beach and the individual crystals can be seen with the naked eye in the lava on the sides of the beach (see Olivine (Mg,Fe)2SiO4 – DP/EC38).

The two main types of lava flows on the island are pahoehoe and 'a'a. These types of flows are easily identifiable by sight using the following characteristics:

Pahoehoe	'A'a
smooth	rough
billowy	jagged
ropy	clinkery

The difference between the two types of flow appear to be related to the temperature, viscosity, and flow rate of the lava. The following table provides the general differences between the two kinds of flows, though there are some other differences provided in the references:

Flows do not always stay the same throughout. Pahoehoe flow will change to 'a'a if the flow rate or viscosity increase, or temperature decreases. This often occurs further away from the source of the lava flow. However, 'a'a flows will not change to pahoehoe flows.

Pahoehoe flows are made up of a series of lobes called toes. The lava slowly flows out and the surface cools forming an isolating skin. The lava underneath continues to flow, maintaining its temperature. Eventually, the very end of the lobe, the toe, cools and caps the end of the flowing lava. If the eruption continues, pressure from the lava inside the toe breaks the cooled surface of the toe, usually at the bottom where the toe meets a prior toe, and a new lobe forms. If a lobe empties of lava before cooling, a lava tube (see Hawaii Volcanoes N.P. - Rain Forest & Lava Tube) is formed, otherwise the tube is solid.

Pahoehoe flows can be further subdivided by their surface texture:

• Ropy pahoehoe – wrinkled surface (most common); caused by the solidified surface being dragged into downstream surfaces by the moving lava underneath

• Entrail pahoehoe – Multi-lobed and relatively smooth (likened to intestines); forms on steep slopes

• Pahoehoe blister – A solidified bubble formed by gas escaping from the lava, usually very thin walled

• Pahoehoe lava coil – Ropy pahoehoe that has curled into a spiral, caused by one part of the undrlying lava flowing faster than the adjacent lava

• Pahoehoe toe – The rounded ends of a flow

'A'a flows have a rough surface, relatively solid center, and sometimes a rough bottom surface as well. The rough surface forms from the cooling of the outer surface then the thick moving center pulling apart the cooled chunks and tumbling them around on the surface. These cooled chunks on the top of the flow are called clikers because they really to create a clinking sound as they are knocked against each other. The bottom rough surface are clinkers at the front of the flow that have rolled down the front of the flow then are subsequently buried by the flow. The middle of the flow is the portion that stays warm enough to keep flowing, moving the flow down slope.

'A'a flows can be subdivided into the following two types with the following characteristics:

Logging requirements:
Send me a note with :

1. The text "GC5CX7Y Queens Highway Flow Types" on the first line.
2. The number of people are in your group.
3. At the EarthCache coordinates identify the kind of flow at the surface? Can you identify a sub-type?
4. At the Q4 coordinates identify the kind of flow at the surface.
5. At the Q5 coordinates, starting at the bottom of the road cut, identify the types and if possible sub-type of the flows? Provide observations for your classifications.

The following sources were used to generate this cache:

• http://hvo.wr.usgs.gov/volcanowatch/archive/1999/99_05_27.html
• http://volcanoes.usgs.gov/images/pglossary/aa.php
• http://volcanoes.usgs.gov/images/pglossary/pahoehoe.php
• http://volcano.oregonstate.edu/what-are-different-types-basaltic-lava-flows-and-how-do-they-form
• http://www.geo.umass.edu/xrf/Composition_of_HSDP-2_Lavas.pdf
• http://www.cr.nps.gov/history/online_books/hawaii-notes/vol4-2-7d.htm
• http://www.geology.sdsu.edu/how_volcanoes_work/Basaltic_lava.html

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