When lava is underground in its molten state it is called magma. As it reaches the ground, and air, it is called lava. Once lava begins to harden it can turn into a variety of shapes and colors. The color of lava depends on the temperature of the flow as well as the chemical composition and any impurities that are in the liquid rock. Colors can include black, red, gray, brown and tan, metallic sliver, pink, and green. Some lava has peridot (olivine) in it which are beautiful olive colored semi-precious crystals that, once they weather and break apart, are responsible for our famous green sand beaches.
When lava cools it also forms a myriad of different shapes and types of lava. There are two main types of lava pahoehoe (pa-hoy-hoy) and a'a (ah ah). Pahoehoe lava comes out smooth and dense and can form large areas that resemble flat parking lots or smooth bumps. A'a, on the other hand, forms individual rocks on the surface anywhere from a few inches to many feet in size. The rocks are porous and very jagged. Below the surface a'a is extremely dense. In general, pahoehoe is very easy to walk on and a'a is very difficult, if not nearly impossible, to walk on (at least without getting hurt).
A third type of lava, pillow lava, forms only underwater and is created by lava entering the ocean underwater where the pressure of the ocean pushes against the lava to form pillow-like shapes that cool very quickly due to the ocean water.
Pahoehoe Lava is one of the most interesting forms of lava. Since it tends to flow more as a thick liquid it can pour uphill as well as downhill and can create a huge variety of interesting shapes.
If pahoehoe lava flows over a fairly flat ground it will coat the ground much like a parking lot - with a thick, smooth, flat coating of lava. However, when pahoehoe encounters barriers in the way, such as rocks, hills, fissures and bumps, it flows over and around them and produces different shapes.
One of the more interesting types of pahoehoe lava is called ropey pahoehoe and looks like a series of twisted ropes spaced evenly along the ground. The twisted ropes may be fairly straight, or may loop and wind in and out much like a fingerprint. Many visitors express interest in what could create such an unusual shape, but once you see ropey pohoehoe lava being created it is instantly clear how the shapes occur. As the pahoehoe flows, it usually encounters some minor barrier that slows up the front of the flow. As the front of the flow is slowing down, the faster flow behind it pushes the front and forces it to create a small ridge, which it pushes up and over the barrier. That ridge begins to cool and creates the next barrier, which in turn creates the next. The result is a series of ridges interspaced with valleys - which looks like 4 inch thick ropes of lava laying side by side or looping side by side. To walk over ropey pahoehoe it is best to walk on the top of the ridges, perpendicular to the ridges.
While ropey pahoehoe is an official name for that particular formation of lava there are a number of other different types of pahoehoe lava - of which we have given our own name but these are not official. One type of especially metallic lava we call quiet flow. Normally, pahoehoe lava sounds like styrofoam being walked on - but quiet flow is much denser and when you walk from normal pahoehoe lava up onto quiet flow your footsteps immediately become softer. The quiet flow pahoehoe also is much more metallic and whereas normal pahoehoe sounds like rock if you break a bit, the quiet flow pahoehoe sounds like Christmas tree ornaments breaking - a light tinkling of glass. Quiet flow pahoehoe also tends to produce very glassy hollow bubbles, which if broken also sound like glass hitting a floor. The quiet flow lava is far denser than normal pahoehoe and we have witnessed a regular pahoehoe flow suddenly producing a quiet flow, and then reverting back to a normal flow.
Another unofficial, but yet different type of pahoehoe lava we call black flow. Black flow lava is especially dark and has a rougher feel to it. Black flow tends to create large mounds and coat tumulus and is much harder to walk on than normal pahoehoe flows. You can usually tell a black flow from other types of flow because it is extremely dark and looks like it isn't much fun to walk on. In general we try to skirt around black flows just because it is much more difficult to hike on.
All the differences in pahoehoe flows stems completely from the temperature of the lava as well as chemical composition. Since both can change during a flow - it is possible to get all types of pahoehoe flowing from a single flow, over time.
We have an internal disagreement about a'a lava. I say that it is one of the worst lavas in the world - almost impossible to walk over and if you ever wanted to get revenge on an enemy you would strip them naked and leave them stranded in the middle of an a'a flow - they would certainly not get out alive. Others in our team say that really, a'a is not that hard to walk on and really wouldn't be that big of a deal to get out of.
A'a lava looks completely different than pahoehoe lava as it is formed. Whereas pahoehoe lava flows smoothly like water or molasses, a'a lava tumbles in the form of small rocks with very jagged sharp edges. The rocks are very lightweight, as opposed to pahoehoe that is extremely dense, and a'a rocks tend to pile up on each other with a lava front that might be a few feet to 40 or 50 feet high of tumbling red hot sharp rocks.
Below the surface, however, a'a tells a different story. A'a flows, while rocky and sharp on the top, are extremely dense underneath - producing some of the most difficult rock to cut through. Several hikes in the National Park take you past huge boulders of dense solid a'a - looking completely different than pahoehoe which tends to come in layers.
While I do concur that if you are careful, a'a is walkable, it is not something you would want to do if you had a choice. Because you are balancing on rocks, which sit on rocks, it is all too easy for one rock to tip, thus making you lose your balance. Once you fall on a'a (and we are talking cold rock here) - it is all over. You WILL be cut and injured. In the times where we have to cross an a'a flow (which does happen, to get to the best places) we try to find the least area to cross to minimize any possible injury. (If you have gloves and need to cross a'a, you might consider wearing them, if you're not already)
Another form of lava is officially named Pele's Hair. This is a wonderful form of lava, and most unexpected. It is also one of the few lava forms that you can create yourself (though nature produces some of the best examples).
Pele's hair looks like long strands of greenish-gold hair. In bright sunlight it is a shimmering gold color, perfectly straight and as thin as human hair. The lengths can be anywhere from particle sized to several feet long, though most Pele's hair that you will encounter (unless it is brand spanking new) will be in the 2 to 6 inch length.
Pele's hair is created when molten lava is ejected into the air - as happens when lava fountains or enters the ocean and explodes. If the airborne molten lava is small enough, and the wind is strong enough, the wind will pull the lava droplet and turn it into a hair-sized piece of rock. It is as if the wind extruded "rock wire" from the liquid mass, much as wire is created in a factory.
You can find Pele's hair all over the place, but mostly near vents, skylights and the ocean entry. Crevices in the ground or areas where rocks form a corner are locations where the blown Pele's hair can collect. Be careful though, Pele's hair while only the size of human hair it is like glass fiber and is very sharp. It is easy to get a small piece stuck in your hand while you are examining it, if you are not careful. (Gloves can be useful in this situation.)
You can create your own Pele's hair by trying to take a sample of pahoehoe flow. When you dip a kitchen whisk, or other implement, into an active pahoehoe flow, as you extract the sample - if you do so quick enough, strands of hair will extrude from your sample back to the ground. These may be many feet in length but only as thin as human hair. These fragile strands do not last long, but show you exactly how they are created.
Pele's tears are another form of lava related loosely to Pele's hair. Just as with Pele's hair, Pele's tears start out being small molten bits of lava sent hurtling into the air due to an explosion or, more often, lava fountain. However, the difference is that the wind is not strong enough to extrude the lava into strands - but instead, the bits tumble back to earth and form round, oval and more importantly, tear shaped bits about 1/4 to 1/2 inch in size. By the time the tears hit the earth they have fully cooled and retain their oval or tear shape.
There are many places within the Hawai'i Volcanoes National Park where there are literally acres of Pele's tears. Quite a bit is right along the roadway and it is fun to park and go look for Pele's tears. Because the tears are the result of fountaining fissures, anywhere there was a fissure that fountained you can find the tears downwind. Good places to look include the area on both sides of the road between Devastation Trail and Kilauea Crater on Crater Rim Drive, as well as the first 1/4 to 1/2 mile on either side of the road on Chain of Craters Drive.
Lava bombs can be thought of as Pele's tears taken to an extremely level. Formed the same way; lava bombs are HUGE blobs of molten lava ejected high into the air. As these blobs fall to earth they rotate and gravity converts them into round and oval rocks that hit the earth already cooled. These are huge rocks, ranging from several feet in diameter to the size of cars, and while you might be able to escape a fountain of Pele's tears, you would never escape a fountain of raining lava bombs.
Lava bombs can be found all over the Big Island. There are many fine examples within the Hawai'i Volcanoes National Park but some of the best examples can be found on the road up to the Mauna Loa Weather Observatory off Saddle Road, as well as the upper road around Mauna Kea (4-wheel only). On Mauna Kea there are huge fields (hundreds of acres) where there are perfect lava bombs every 3 to 5 feet - spaced as if planted - an amazing site to behold.
Where else can you go and find Green Sand Beaches - other than Hawai'i (probably a few places, but not many). Actually, Hawai'i has many different colors of sand. Black, gray, brown and green sand beaches are from lava of various compositions, whereas pink and white sand beaches are from coral.
Green sand comes from the semi-precious gemstone peridot, a form of olivine. Occasionally a flow will be very rich in olivine crystals and the rocks produced by this flow will have a distinctive greenish hue. Close examination of the rocks will show small crystals, some as large as 1/4 inch in size, of bright olive green.
Olivine is very susceptible to breaking down in water, so large crystals (gem-sized) are rare, but occasionally someone finds a wonderful multi-carat sized gem. Usually the crystals are tiny and form a green sand of pure crystals. There are many places on the Big Island where you can find green sand. Even up in the Hawai'i Volcanoes National Park you can find green sand on the hike to Pu'u Huluhulu, as well as on the Hike to 'Ainahou Ranch. However, the best examples of Green Sand can be found down at South Point. As you get to the boat launch ramp at South Point you will see, amidst the bright red dirt, quite a bit of greenish colored sand. If you actually take the hike out to the Green Sands Beach, you will encounter a large lava cone at the ocean edge that is entirely made up of olivine crystals. This is the remains of a large cone that had a very high concentration of olivine. Much of this has eroded into the ocean where the currents have brought it back up to form this unusual and perfect green sand beach.