CASSIOPEA
'UPSIDE DOWN JELLYFISH'

Filmed at the London Aquarium.

'Sometimes this jellyfish is picked up by the crab Dorippe frascone and carried on its back. The crab uses the jellyfish to defend itself against possible predators.'

PAHOEHOE

Pahoehoe is a Hawaiian term for basaltic lava that has a smooth, hummocky, or ropy surface. The surface texture of pahoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture: Entrails, Toes, Blisters, Coils and Ropy.

Named after the texture of an animal's intestines 'Entrail' pahoehoe best forms when pahoehoe flows down a steep slope. It is usually found on the sides of rootless vents, such as hornitos and ruptured tumuli.

Small protuberances called 'Toes' are common along the edges and flow front of an active pahoehoe flow moving across flat or gentle slopes. The flow spreads as the small toes grow in size and merge together to form a broader front, which in turn inflates with new lava moving through the molten core of the flow. Another series of budding toes will break out, move forward, and start the process over again.

'Blisters' are thin-walled basaltic-glass bubbles formed by the release of volcanic gas from the surface of a pahoehoe flow. Like a glass blower that blows air into molten glass to create a goblet or vase, gas released from lava may force the thin glassy crust of a lava flow to form a large bubble or blister.

Lava 'Coils' are spiral or scroll-shaped features that form along slow-moving shear zones in a flow; for example, along the margins of a small channel. The direction of flow can be determined from a lava coil.

'Ropy' pahoehoe is the most common surface texture of pahoehoe flows. The numerous folds and wrinkles ("ropes") that are characteristic of ropy pahoehoe form when the thin, partially solidified crust of a flow is slowed or halted (for example, if the crust encounters an obstruction or slower-moving crust). Because lava beneath the crust continues to move forward, it tends to drag the crust along. The crust then behaves like an accordian that is squeezed together--the crust is flexible enough to develop wrinkles or a series of small ridges and troughs as it is compressed and driven forward.

ICELAND
Heiðmörk and þingvellir

A trip taken in 2010

GEODES

'In the Greek language, geode means "shape of the earth", and geodes are round like earth or oblong like an egg. Geodes are created in the hollow areas of soil such as animal burrows or tree roots. They are also formed in the bubbles in volcanic rock.

It can take hundreds of millions of years for the space inside a geode to be filled, and many geodes remain partly hollow. A geode which is completely filled with crystals is called a nodule. Agate-filled nodules are called thunder eggs.'

PRINCE RUPERT'S DROP

'If the glass is so shaped as to be of unequal thickness in its different parts, it can seldom be cooled without fracture, and, if unbroken when cool, is liable to fracture with any subsequent change of temperature or by a sudden jar. Often this fracture takes place, in articles of considerable thickness, with an explosive force, perhaps breaking the glass into a thousand pieces. When glass breaks in this manner, it is said to "fly."
William Leighton, January 1876, Popular Science Monthly