READ THIS FIRST!!!
THE OBSERVATIONS FOR THIS EARTHCACHE CAN BE DONE AT EITHER THE NORTH OR SOUTH REST AREAS. YOU ONLY NEED TO VISIT ONE OF THE REST AREAS. THE POSTED COORDS ARE FOR THE LAVA TRAILS AT THE NORTHBOUND REST AREA. THERE IS A WAYPOINT FOR THE LAVA TRAILS AT THE SOUTHBOUNT REST AREA.
ABOUT THIS EARTHCACHE
For this EarthCache, you will be exploring the Lava Trails at either the north or south rest areas. There are Lava Trails at both rest areas. Sections of these trails are closed during winter months.
You will be able to make your observations and answer the logging questions from the sections of the trails that don't close.
LOGGING REQUIREMENTS
In order to log this EarthCache, send me your answers to the following questions either through email or messaging from my profile page.
1: What type of lava (pahoehoe or A'a) makes up the lava field here?
2: How many of the features listed below can you find? Pick one and describe the size and shape.
3: Post a pic of you or a signature item with the "LAVA FORMATIONS" sign in the background.
WHY HERE?
When most people think of lava, they think of volcanos blasting lava and fiery rocks high into the air with explosive force. Here, however, lava oozed gently from a deep crack 30 to 50 miles deep. A red hot river of lava flowed here around 4,100 years ago where a weak spot in the earth's crust opened and lava flowed out. This molten lava bubbled and oozed at 2,000 degrees F. Now long cooled, this lava flow is part of an extremely harsh environment known as the high dessert. This lava flow is relatively young and not covered with soil or vegetation which allows us to see all the features it has to show us.
GEOLOGICAL HISTORY
Geologists estimate that the Hell's Acre Lava Field was created about 3250 BC. The lava field was created by the Lava Ridge-Hell's Half Acre fissure vent, and marks the southern edge of this area of volcanic activity. This fissure vent was created when one or more magmatic dikes (sheets or tubes of magma cutting across the existing geologic features) found their way to the surface. At the northwestern edge of the lava field is a basaltic volcano, with the fissure vent extending toward the southeast and the Hell's Half Acre site. The basaltic volcano is a shield type. Pit craters and spatter cones follow this active fissure line. Two non-erupting fissures extend northwest from the shield volcano for about 2.7 miles. One scientific team hypothesized that the seven lava fields in the vicinity of Hell's Half Acre may belong to as few as two fissure vents.
Hell's Half Acre was created when basaltic pāhoehoe quickly flowed out of the volcanic rift. At least eight lava lobes have been identified by geologists. As magma and volcanic gases drained from underneath the lava field, the field subsided—leaving behinds hummocks, or "hills" of lava (a feature which Hell's Half Acre retains today). There is evidence that lava filled and drained the lava lake numerous times, and that lava repeatedly overflowed the lake.
Lava from the fissure vent tended to flow downhill toward the southeast, covering part of the fissure. Lava tubes extend in a generally southeastern direction under the lava field, and surfaced in the far southeastern corner of the site. There is also evidence that later pāhoehoe lava lobes ran underneath or inside existing lobes, and then broke out.
FEATURES
dome
A steep-sided rounded accumulation of highly-viscous silicic lava over a vent.
fissure
An elongated fracture or crack at the surface.
fracture
The breaking of a mineral other than along planes of cleavage. Also, any break in a rock such as a crack, joint, or fault.
lava blister
A hollow upwelling, usually with a diameter of approximately 1 meter, on the crust of a lava flow formed by expansion of gas or vapor beneath the surface.
vesicle
A cavity of variable shape formed by the entrapment of a gas bubble during solidification of molten rock material.
references
https://www.nps.gov/subjects/volcanoes/index.htm
https://en.wikipedia.org/wiki/Hell%27s_Half_Acre_Lava_Field
https://www.blm.gov/visit/lava-trail-system-hells-half-acre
https://sciencenotes.org/types-of-lava-pahoehoe-and-aa/
I have earned GSA's highest level:
 |