Lapilli is a size classification term for tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. Lapilli (singular: lapillus) means "little stones" in Latin.
By definition lapilli range from 2 to 64 mm (0.08 to 2.52 in) in diameter. A pyroclastic particle greater than 64 mm in diameter is known as a volcanic bomb when molten, or a volcanic block when solid. Pyroclastic material with particles less than 2 mm in diameter is referred to as volcanic ash.
Formation: Lapilli are spheroid, tear drop, dumbbell or button-shaped droplets of molten or semi-molten lava ejected from a volcanic eruption that fall to earth while still at least partially molten. These granules are not accretionary, but instead the direct result of liquid rock cooling as it travels through the air.
Lapilli may consist of fresh magma, solid magma from a prior eruption, or basement rocks through which the eruption passed. Accretionary lapilli are pellets formed by the accretion of volcanic ash or dust around moisture droplets; as in hailstones formed of water, these volcanic “hailstones” may show concentric rings—some as much as 10 cm (four inches) across—when they are carried through the eruption cloud several times by turbulent updraughts. When they fall into the sea, they cool quickly, hardened and and can be preserved on the ocean floor.
These deposits of lapille formed bands which run for more than 40km in the Barberton Greenstone Belt. Very large and long lasting volcanic eruptions must have filled the air with dark clouds of ash and steam for many months or years.
To log this EarthCache you have to e-mail me the answers to the following questions:
1. Take the water you brought and pour it over the grayish rock nearest to the panel of the Volcanic Lapille and give a short description of what you see (including the amount and size of the lapille).
2. What is the approximate size of the specimen?
3. What kind of rock do you think this lapille are preserved in?
4. When was this lapille formed according to the panel?
Uploading photos to the cache page is the best way to say thank you to the cache developer and to encourage others to visit the location but is only optional.
NOTES:
- There are no other facilities along the trail except for very nice picnic spots.
- The distance is about 40km from Barberton on a narrow and winding road up to the Bulembu border post to Swaziland. No or little cellphone reception is available.
- You can email me your answers in either Afrikaans or English.
Note that a handy guidebook specially compiled for this route is on offer at Barberton Tourism in town.
Enquiries: 013-712 2880 or www.barberton.co.za
Guided tours by Tony Ferrar on 072-376-2581 and Dave Mourant on 082-923-5366.
Thank you to the Barberton Chamber of Business and all those involved to develop this geotrail.
