It can easily break when you step on it which may result in badly scratched legs because the edges of a broken lava flow are razor sharp. As mentioned earlier, lava crust solidifies quickly, but the interior keeps moving which often leaves empty space beneath the thin surface. However, hiking on a smooth lava surface is not without some nasty surprises. Walking on a pahoehoe lava flow is relatively easy, especially when compared with walking on an aa-type lava flow which is practically impossible undertaking. Pahoehoe lava flows form a beautiful and otherworldly barren landscape in southern part of Hawai’i. If you are also trying to find flowing lava, always try to keep a safe distance with such a thick cocktail of hazardous gases and pay attention to the wind direction. Here is a picture of volcanic gas seeping out from the ground. I tried to be very careful, trying to observe the flows so that the wind was blowing the gas away from me. But because of toxic volcanic gases that are involved with all types of lava flows. This is potentially very dangerous situation not so much because of lava itself because it moves slowly and contrary to popular belief it is impossible to sink into it. The red glowing material was just seeping out of the ground here and there, some in front of me and some already behind. When I was hiking in Hawaii with a clear target in my mind to find an active lava flow I was perplexed and amazed when I suddenly discovered that I am actually standing right in the middle of such a flow. The lava often flows largely underground. That is indeed often the case, but it is also very common that there is no easily defined boundary of an active lava flow. Lava flows are often imagined as fiery rivers of molten rock. Hawaiian lava from the Kilauea volcano (Pu’u O’o vent). Pahoehoe is also known as ropy lava and it has several more varieties named entrail, festooned, filamented, sharkskin, shelly, etc 4. Blocky lava is composed of larger blocks than aa lava and these blocks have much smoother surface.īest known examples of pahoehoe lava flows are from the Big Island of Hawaii and the term ‘pahoehoe’ itself (just as ‘aa’) originates from the Hawaiian language. Blocky lava needs more felsic compositions (silica content generally over 55%). Aa lava can be basaltic, andesitic, tephritic, etc. Aa lava is much more common and is not as picky about the composition of lava flow. Only low-viscosity (usually basaltic) lava can form pahoehoe. Lava flow that was originally pahoehoe may transform into aa lava but the reverse is impossible - once lava crust is broken it can not return back to smooth and continuous form 3. Pahoehoe and aa lava are strikingly different in appearance, but their composition may be identical or very similar. Higher effusion rate results in lava flow being shattered which is how the rubbly and clinkery aa lava surface forms. Pahoehoe lava flow is usually at least 10 times slower than typical aa lava flow 5. Pahoehoe is a smooth and continuous lava crust. Pahoehoe forms when the effusion rate is low and consequently the velocity of lava flow is slow 2. Lava surface may cool from bright yellow to dull red within minutes. Pu’u O’o vent, Kilauea volcano. Dull red colors indicates a temperature in the range of 600…700 ☌. Bright yellow is hotter (over 1000 ☌) and orange cooler (800…900 ☌). The temperature of glowing lava is at least 475 ☌. The most common subaerial lava flows today are pahoehoe, aa, and blocky lavas. That enabled the lava to flow more easily and turbulently. Turbulent lava flows may have been present billions of years ago when the interior of the Earth and consequently lava flows as well were significantly hotter and the composition of lava was less siliceous. Sometimes Turbulent lava flow is also added, but the latter is only of theoretical interest to scientist because we will not see that type of lava flow in the nature. The most common way to divide lava flows into distinct types is following: Pahoehoe lava flow, Aa lava flow, Blocky lava flow, and also Pillow lava flow. The lava type associated with submarine volcanism – pillow lava, is therefore underrepresented where ordinary people have a chance to see it. Lava flows are very common features on planet Earth although the vast majority of them are hidden from us in the deep ocean basins. Transition from smooth pahoehoe to rubbly aa.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |