The western half of the Arabian Peninsula contains not only
large expanses of sand and gravel, but extensive lava fields known
as "haraat". One such field is the 14,000-square-kilometer Harrat
Khaybar, northeast of the city of Al Madinah (Medina). The volcanic
field was formed by eruptions along a 100-kilometer, north-south
vent system over the past 5 million years. The most recent recorded
eruption took place between 600-700 AD. [source: NASA].
On several places the lava formed the famous lava
tubes. This earthcache invites you to explore this
geo-morphologically unique and interesting phenomenon. The
wikipedia source describes it:
Lava tubes are a type of lava cave formed when an
active low-viscosity lava flow develops a continuous and hard
crust, which thickens and forms a roof above the still-flowing lava
stream. Tubes form in one of two ways: by the crusting over of lava
channels, and from pahoehoe flows where the lava is moving under
the surface.
The best description of various aspects and parts of lava tubes,
I have found at the website Virtual Lava Tube. The pictures there are from
Hawai but the description is general.
The lava tubes found here have also an interesting,
non-geological history. The http://www.saudicaves.com/ site in
an article about the region indicates that some of
these long and impressive caves were vital to man's survival
because they acted as reservoirs for the most precious substance in
Arabia - water.
Cache access and difficulty
It is not easy to get to the cache, and you definitely need a
4x4 car. From the waypoint 1 on the main road (15), you follow a
new tarmac road to the east up to the waypoint 2 where you turn
right on a track through some wadis and lava fields. There are more
tracks and you will need to find the right one (sometimes by a
trial-and-error). Be careful and consider not to drive alone - just
in case something happens to the car.
The 5* terrain indicates partly the driving skills you need and
partly the scrambling to the tube and exploring the cave itself.
The 3* difficulty indicates the ability to navigate.
How to claim the cache
-
Explore the lava tube. You can descent down (just on one place)
without any climbing gear. Then the entrance on your left is only a
short cave. But the right entrance is worth to explore more. You
can walk several hundred meters, come to another opening, climb up
and see your parked cars in a distance. Your geodetic task is to
email me an answer to a simple question: Is the connection between
the two entrances a straight line, or a curve?
-
The second question (to be emailed) is more theoretical: What is
the origin of the word "lava" (a word that is similarly used and
spelled in most languages). The reason of this question is to point
to the geo-morphological characteristics of lava.
-
Optionally, you are welcome to add your picture to the log.
Especially appreciated are pictures of the cars in distance from
the other tube entrance.