The Hawaiian Islands were formed by erupting volcanoes. So let's follow our Hawaiian theme with a volcanoes theme, beginning with a pair of Hawaiian volcano-words, for which the links give photos.

aa – lava having a rough surface [Hawaiian, 'to burn']
pahoehoe – lava with a smooth, glassy or rippled surface. [see also here]
[Hawaiian, reduplication of hoe, 'to paddle', probably from the swirls on its surface]

Not all lava is the same: A pahoehoe (pa-hoy-hoy) lava flow travels quickly and often forms smooth, ropy patterns, while an aa (ah-ah) lava flow moves slowly and hardens to form sharp chunks.
– Mackie Rhodes, Instructor, March, 2004

lahar – an mud-flow "avalanche" of volcanic ash and water, down the slopes of a volcano
[Javanese for lava']

Lahar and other volcanic debris cascaded down the slopes of Mt. Bulusan yesterday after heavy rain, sending residents in Casiguran and Irosin to flee to higher ground.
– Manila Standard Today, June 22, 2006

solfatara – a volcanic area that gives off sulfurous gases and steam
[from the Italian and Latin for 'sulfur']

St Lucia … seems to have everything: spectacular mountain scenery, a drive-in volcano with solfatara (steaming sulphur springs and malodorous gases that signify an active, but not apoplectic, volcano), a wild rainforest and a privately owned semi- tame one (the botanical gardens).
– Victoria Pybus, The Independent, July 11, 1998

Bonus word:
apoplexy (adj. apoplectic) – a fit of extreme anger; rage
[also the name of a medical condition]

My ex husband was very much into geology and I picked up a lot of the vocabulary from him.

The volcanic term I always remember is nuée ardente which means "burning cloud".

The English term is Pyroclastic flow or pyroclastic cloud.

My ex used to tell me the story of a man in St. Pierre who survived the eruption of Mt Pelee in 1902 because he was in the town's jail - the thick walls of which protected him!

fumarole – a hole in a volcanic area from which hot smoke and gases escape (see link)
[Italian, from Late Latin for 'smoke hole', diminutive of 'smoke chamber']

Down on the crater floor, [robot] Dante will play the role of field geologist, collecting information that Kyle and his colleagues have long desired. Most important, the robot will study the vapors rising from volcanic vents called fumaroles. … Escaping from inside the Earth, these gases contain clues about the source of the magma feeding Mt. Erebus. "For volcanoes, these gases -- the volatile elements like carbon dioxide and water--are like blood for a human being. They are the life body of a volcano," says Kyle.
– Richard Monastersky, Science News, June 6, 1992

Bonus word:
magma – hot fluid or semi-fluid rock within the earth’s crust

caldera – a crater formed by volcanic explosion or by collapse of a volcanic cone.
[Spanish 'cauldron']

This island is still growing, as a river of molten lava pours often from the caldera into the sea and has long been considered a spiritual place …
– Cultural inspiration on Hawaii's Big Island, Sunset, July, 2004

I spend two nights at the Lake Yellowstone Hotel, … a survivor of legions of tourists, … all drawn by the pageant of wildlife atop an ancient caldera. Miles below, like a buffed ember, is a hot spot through the crust, and the caldera awaits its wakeup call from a 600,000-year nap.
– Kerrick James, Travel America, May-June, 2004

tephra – solid matter ejected into the air by an erupting volcano
[Greek tephr, ash]

The 1980 eruptions of … Mount St. Helens showed that even relatively thin accumulations of tephra can disrupt social and economic activity over a broad region. Downwind, … Spokane received between 1 and 8 centimeters of ash and came to a near standstill for up to 2 weeks.
– Sid Perkins, Science News, Nov. 24, 2001