Lava is liquid rock discharged from a volcano. Its speed and distance of flow and density are related by the amount of silica that makes up the lava. Basaltic lavas are low in silica and generally erupt at high temperatures (1740° F). Viscosity can be low resulting in quicker flowing lava that will likely travel farther from the volcanic vent than other types of lava. It is possible for basaltic lava thickness to be greater than that of the moving lava flow at any given time due to the lava’s traveling beneath a solidified lava crust. Most basaltic lavas are a'a (ah ah) or pahoehoe (pa-hoy-hoy) types.
A’a lava is more common than pahoehoe. It tumbles in the form of individual rocks ranging in size from a few inches to many feet. These rough, angular broken lava blocks are called clinker. The rocks tend to be lightweight and porous with jagged edges. They often stack upon each other to form a lava front up to 50 feet high. The flow’s exterior will display widespread fracturing which allows the whole front to make steady progress as a single entity. The lava flow may move like a wall of chunks as it crashes through, pushing down anything in its path. An a’a lava field is sharp and rocky on the top but dense underneath.
Whereas a’a lava is rough and jagged, pahoehoe emerges smooth and extremely dense. Formations of this type lava are often large and flat. It thickly coats the ground as it flows. The lava tends to have more localized cracking of the crust which allows it to travel by individual lobes or toes. When it engages obstacles such as bumps, hills and rock, pahoehoe lava will flow around, over or slowly burn them, producing different shapes in the interim. The surface of cooled pahoehoe lava can have a smooth, billowy, and/or ropy appearance.
Examine the Hawaiian lava sample on site. In an email or message through my profile on the Geocaching web site, please provide the following information. Do NOT put your answers in your log. Please note. There are no right or wrong answers. I am looking for your thoughts based on your inspection of the lava and the information above. You do not need to wait for me to respond to your message before logging. However, logs without the answers being sent will be deleted without notice.
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Describe the texture of the lava. Is it smooth, sharp, dense, porous, etc.?
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Do you think this is from a pahoehoe or an a'a flow? Why?
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Optional:Take a picture of you on site. Please no spoilers though.
Sources:
http://www.instanthawaii.com/
http://hvo.wr.usgs.gov/volcanowatch/archive/1999/99_05_27.html