Jaskinie lawowe - zarys problematyki
Abstract
Jaskinie rozwinięte w lawach są stosunkowo słabo znane pomimo tego, że są one częstym zjawiskiem w wielu rejonach świata. Większość takich jaskiń to fragmenty tzw. rur lawowych. Powstanie rur lawowych jest związane ze spływami lawy bazaltowej. Najczęściej rury takie są rozwinięte w lawach pahoehoe cechujących się małą lepkością, lecz znane są także z law aa o większej lepkości. Powstanie rur lawowych jest wynikiem różnych procesów. Najczęściej jest efektem rozwoju skorupy ponad płynącym strumieniem lawy. Taka skorupa ostatecznie pokrywa cały potok lawowy. Powstaje ona dzięki gradientowi termicznemu pomiędzy płynącą lawą a atmosferą. Rury lawowe są dobrymi izolatorami cieplnymi i pełnią rolę kanałów dla strumieni lawowych płynących na duże dystanse. Dlatego też powstanie rur lawowych jest bardzo istotnym czynnikiem dla rozwoju rozległych spływów lawowych. Płynąca lawa powiększa rurę lawową na skutek erozji termicznej i mechanicznej. Dzięki temu wewnątrz rur lawowych powstają wcięte meandrujące koryta, lawospady, świetliki i toczeńce lawowe. Inne charakterystyczne elementy rur lawowych jak półki znaczące dawny poziom potoku lawowego, wały przykorytowe, wewnętrzne rury są efektem akrecji lawy wewnątrz rur lawowych. W jaskiniach lawowych występują też różnorodne speleotemy zbudowane z gipsu, węglanu wapnia i opalu.
LAVA TUBE CAVES – GENERALS
Summary
Caves developed in lavas are not broadly known despite the fact that they are quite a common phenomenon in some parts of the world. Majority of such caves form as lava tubes and they are called lava tube caves. The origin of lava tubes is related to flowsof basaltic lava. They are mostly developed in a low-viscous pahoehoe type of basaltic lava, but some caves located in a viscous a lava are also known. The origin of the lava tubes has been ascribed to various mechanisms. The most frequent seems to be the growth of stationary crust over a flowing lava stream. Finally, this crust completely roofs a lava stream. This is brought about by a contrastingthermal gradient between the flowing lava and the atmosphere. The lava tubes are good heat isolators and they act as long conduits for flowing lava. Thus, they are a very important factor for propagation of lava and the origin of broad lava flows. The flowing lava widens the tube as a result of thermal and mechanical erosion. The above processes form several characteristic features of lava tube interior, e.g. incised meandering channels, lavafalls, skylights, lava balls. Other features, for example, lateral benches, internal levées, tube-in-tube structures, are effects of lava accretion inside the tubes. Various speleothems made of gypsum, calcium carbonate, as well as opal can form in lava tube caves.
LAVA TUBE CAVES – GENERALS
Summary
Caves developed in lavas are not broadly known despite the fact that they are quite a common phenomenon in some parts of the world. Majority of such caves form as lava tubes and they are called lava tube caves. The origin of lava tubes is related to flowsof basaltic lava. They are mostly developed in a low-viscous pahoehoe type of basaltic lava, but some caves located in a viscous a lava are also known. The origin of the lava tubes has been ascribed to various mechanisms. The most frequent seems to be the growth of stationary crust over a flowing lava stream. Finally, this crust completely roofs a lava stream. This is brought about by a contrastingthermal gradient between the flowing lava and the atmosphere. The lava tubes are good heat isolators and they act as long conduits for flowing lava. Thus, they are a very important factor for propagation of lava and the origin of broad lava flows. The flowing lava widens the tube as a result of thermal and mechanical erosion. The above processes form several characteristic features of lava tube interior, e.g. incised meandering channels, lavafalls, skylights, lava balls. Other features, for example, lateral benches, internal levées, tube-in-tube structures, are effects of lava accretion inside the tubes. Various speleothems made of gypsum, calcium carbonate, as well as opal can form in lava tube caves.