altough the link is brazilian, it seems to be named the same


The Quixaba Formation (Almeida, 1955) is a sequence of black flows of alternating ankaratrite lava and pyroclasts containing components of the same lava. This formation rests on two step-like plateaus of the main island; the eastern one may reach 180 m of exposed thickness above sea level. This formation also occurs in some islands, particularly the Rata Island. The flows are generally horizontal, but may show dips as steep as 30º to the south, concordant to the flow direction of the lava. The flows are massive in its interior but vesicular or amigdaloidal at the base and mainly at the top (Figure 10). Their thickness may exceed 40 m at the shore cliff of the Sancho Bay, but it is generally just a few meters thick. Flows of melilite ankaratrite (Figure 11), as thin as two centimeters of thickness, were seen in alternation with lapilli-tuff containing bombs of the same material. The pyroclastic rocks are tuffs, tuff-breccia, lapilli-tuffs and agglomerates, essentially containing components of the flows, including isolated crystals. Angular blocks of lava may reach 2 m. Perfect bombs and fragments of rope-like lava are not rare. They may form a chaotic group of fragments of several dimensions, or exhibit coarse stratification, locally with fine well-stratified beds. A striking structural feature is the Tamandaré chimney, at the northeast edge of the main island. It has a diameter of almost 130 m and truncates the lower flow. Its walls are of ankaratrite, with remnants of tuff and chimney agglomerate, and crosscut by dikes. The low tide discovers the escoriaceae lava of its interior. It was a place for escape of solutions, where calcite precipitated as perfect scalenohedral crystals, filling fractures on breccia and agglomerates. Dikes of coarse nefelinite were observed in a few points of the main island.
A Formação Quixaba (Almeida, 1955) constitui um empilhamento de negros derrames de lava ankaratrítica alternados com piroclastos de componentes da própria lava. Aflora nos dois planaltos escalonados da ilhas principal, no oriental podendo-se reconhecer até 180 m de espessura exposta acima do nível do mar. A formação constitui algumas ilhas, com destaque para a ilha Rata. Os derrames, quando não são horizontais, apresentam inclinações de até 30º para sul, sentido do escoamento das lavas. Os derrames são maciços em seu interior porém vesiculares ou amigdaloidais na base e sobretudo no topo (Figura 10). Sua espessura varia, podendo ultrapassar 40 m na falésia da baía do Sancho, mas geralmente apresenta alguns metro somente. Vimos derrames de melilita ankaratrito (Figura 11) com menos de dois centímetros de espessura, alternados com tufos lapílicos contendo bombas do mesmo material. As rochas piroclásticas são tufos, tufo-brechas, lapilli-tufos e aglomerados, constituídos essencialmente de componentes provenientes dos derrames, inclusive cristais isolados. Blocos angulosos de lava alcançam 2 m. Não são raros perfeitas bombas e fragmentos de lava cordada. Quando não constituem um conjunto caótico de fragmentos de variadas dimensões, podem mostrar-se com estratificação grossa ou, localmente, em estratos finos, bem acamados. Uma estrutura que nos chamou atenção é a chaminé de Tamandaré, na extremidade nordeste da ilha principal. Tem cerca de l30 m de diâmetro e perfura o derrame inferior. Suas paredes, em ankaratrito, têm restos de tufo e aglomerado de chaminé, sendo atravessadas por diques. A maré baixa descobre a lava escoriácea de seu interior. Foi local de escape de soluções, onde se formou muita calcita que, em perfeitos escalenoedros, preenche fraturas nas brechas e aglomerados. Diques de nefelinito de granulação grossa foram vistos em poucos locais da ilha principal.

Route 66 Excerpt - [ Traduzca esta página ]
... are covered with two kinds of lava: aa(pronounced ah-ah), sharp, hiking boot assaulting
hunks of basalt and pahoehoe (pa-hoy-hoy), smoother, rope-like lava. ...
www.thetrailmaster.com/Route66Excerpt.html - 12k - En caché - Páginas similares

Album: hawaii - [ Traduzca esta página ]
... out the 1969 lava flow Hawai`i Volcanoes National Park Anna checking out th...canoes
National Park, Rope-like lava, Hawai`i Volcanoes National Park Rope-like ...
www.met.utah.edu/zipser/nesbitt/pictures/hawaii/ - 60k - En caché - Páginas similares

Info on the islands - [ Traduzca esta página ]
... black sand beaches including Puerto Egas On the eastern coast of James Island is
Sullivan Bay, a large area of fresh pahoehoe (rope like) lava flows dating ...
staff.esuhsd.org/~balochie/studentprojects/ galapagos/theislands.html - 9k - En caché - Páginas similares

View topic - The 2nd Word - [ Traduzca esta página ]
... (I seem to recall from my geology studies 30 years ago that "aa" is lava that solidifies
as a sharp, pointy surface, and that "pahoehoe" was rope-like lava. ...
www.speedreading.com/phpBB2/ftopic15178-0.html - 71k - En caché - Páginas similares

Types of Lava - [ Traduzca esta página ]
... Those two types are pahoehoe and a`a. Pahoehoe is a low viscosity
lava that when dries is a mass of billows and ropelike coils. ...
www.lapietra.edu/scienceweb/web/178/kilauea/lava.html - 4k - En caché - Páginas similares

Lava and Astronauts on Big Island, Hawaii - [ Traduzca esta página ]
Back Lava and Astronauts. (1997). Pahoe'hoe lava. Gently flowing lava can form
rope-like structures, and you can walk rather easy across this type of lava. ...
www.travelnotes.de/hawaii/bigislan/astro.htm - 4k - En caché - Páginas similares

MSN Encarta - Multimedia - Pahoehoe Lava - [ Traduzca esta página ]
... As it flows, it twists into ropelike shapes. As the lava loses its dissolved gases,
it becomes thick and brittle and forms rough, jagged blocks of rock called ...
encarta.msn.com/media_461569036_761570122_-1_1/ Pahoehoe_Lava.html - 26k - En caché - Páginas similares

Ropy pahoehoe
Ropy pahoehoe is the most common surface texture of pahoehoe flows. The numerous folds and wrinkles ("ropes") that are characteristic of ropy pahoehoe form when the thin, partially solidified crust of a flow is slowed or halted (for example, if the crust encounters an obstruction or slower-moving crust). Because lava beneath the crust continues to move forward, it tends to drag the crust along. The crust then behaves like an accordian that is squeezed together--the crust is flexible enough to develop wrinkles or a series of small ridges and troughs as it is compressed and driven forward.

Related photo glossary terms:
Pahoehoe
Pahoehoe toe
Entrail pahoehoe
Pahoehoe lava coil
Pahoehoe blister




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