SPEAKER 5:YEAH.
RELATIVELY SPEAKING, IT'S A
YOUNG VOLCANO PROBABLY 50
MILLION YEARS OLD OR SO,
WHICH IS IN STARK CONTRAST TO
THE ROCKS IN THE SEDIMENTARY
... PARDON ME, ROCKS IN THE
SHENANDOAH VALLEY, WHICH ARE
CONSIDERABLY OLDER, ALMOST 10
TIMES AS OLD. PROBABLY IN THE
NEIGHBORHOOD OF 400 TO 500
MILLION YEARS OLD. IT STANDS
OUT IN STARK CONTRAST. NOW,
IT'S NOT ACTUALLY A VOLCANO
ITSELF. IT'S SORT THE REMAINS
OF THE PLUMBING FOR A VOLCANO
THAT'S NO LONGER HERE. THE
LAND SURFACE OVER TIME AFTER
IT ERUPTED, IT SIMPLY HAS
ERODED DOWN TO THE LEVEL THAT
WE SEE NOW, WHICH IS
ESSENTIALLY A THUMB STICKING
UP OF ROCK THAT IS MORE
RESISTANT TO WEATHERING AND
EROSION THAN THE SEDIMENTARY
ROCKS AROUND IT. WE'VE KNOWN
FOR SOME TIME THAT THERE HAVE
BEEN VOLCANIC FEATURES NOT
JUST HERE IN THE VALLEY, BUT
THERE ARE ALSO SOME AS YOU GO
A LITTLE BIT FURTHER WEST
INTO HIGHLAND COUNTY AS WELL.
WE'VE
KNOWN FOR SOME TIME THAT THEY
WERE VOLCANIC FEATURES. IT'S
ONLY RELATIVELY RECENTLY THAT
WE'VE BEEN ABLE TO PUT A
NUMBER OF PIECES TOGETHER TO
EXPLAIN THE ORIGINS OF THE
VOLCANO THAT ERUPTED AND HOW
OLD IT WAS, JUST PUT SOME
CONSTRAINTS ON THE TIME THAT
A NUMBER OF STUDENTS AND
OTHER FACULTY HERE THAT HAVE
STUDIED IT FAIRLY EXTENSIVELY
AS WELL AS SOME OF THESE
OTHER VOLCANIC FEATURES.
HISTORICALLY, YOU CAN TALK
... IF YOU GO FROM, SAY,
CHARLOTTESVILLE TO WEST OVER,
YOU'RE TALKING ROUGHLY A
BILLION YEARS OR SO OF
GEOLOGIC HISTORY. WE HAVE
SOME VERY OLD CRYSTAL AND
ROCKS THAT WERE
METAMORPHOSED. THEY WERE PART
OF A MOUNTAIN RANGE THAT'S NO
LONGER HERE CALLED THE
GRENVILLE MOUNTAINS.
THOSE
ACTUALLY FORMED WHEN
CONTINENTAL PLATES CAME
TOGETHER, AGAIN ABOUT A
BILLION YEARS AGO TO FORM A
CONTINENT NOT CALLED PANGAEA,
BUT WE CALL IT RODINIA. THAT
PRODUCED A MOUNTAIN RANGE
THAT ERODED DOWN AND ABOUT
600 MILLION YEARS AGO, IT
STARTED TO OPEN UP AGAIN. IT
RIFTED A LOT OF WHAT'S ON TOP
OF THE BLUE RIDGE IS
GREENSTONE WE CALL IT AND
THAT IS THE REMAINS OF SOME
OF THE LAVA THAT CAME OUT
THEN. AFTERWARDS, IT GOT
REALLY QUIET, KIND OF LIKE IT
IS TODAY, AND WE STARTED
GETTING LOTS OF SEDIMENTS
FILLING IT. AS LITTLE AS 450,
470, 500 MILLION YEARS AGO,
THIS WAS A SHALLOW MARINE
AREA. IT WAS SOUTH OF THE
EQUATOR. THE STORY I LIKE TO
TELL IS TO HAVE PEOPLE
PICTURE BAHAMAS.
IF YOU
THINK BAHAMAS WITH SOFT
TROPICAL BREEZES AND LITTLE
WAVES AND CLEAR WATER AND
WHITE SAND AND PALM TREES AND
SOFT MUSIC IN THE BACKGROUND,
TAKE AWAY THE MUSIC, TAKE
AWAY THE PALM TREES AND
YOU'RE LEFT WITH A LOT OF
WARM SHALLOW OCEAN WHERE
LIMESTONE IS FORMING. THAT
COVERS A LOT OF THE BASIC
PART OF THE SHENANDOAH. IT
EXPLAINS ALL THE LIMESTONE
THAT WE HAVE HERE.
