Aa lava flows are denser and more viscous than pahoehoe, and tend to move slower. Flows can measure 2 to 20 m (7 to 66 ft) thick. Aa flows are so thick that the outside layers cools into a rubble-like mass, insulating the still-hot interior and preventing it from cooling. Aa lava moves in a peculiar way—the front of the flow steepens due to pressure from behind until it breaks off, after which the general mass behind it moves forward. Pahoehoe lava can sometimes become Aa lava due to increasing viscosity or increasing rate of shear, but Aa lava never turns into pahoehoe flow.Hawaiian eruptions are responsible for several unique volcanological objects. Small volcanic particles are carried and formed by the wind, chilling quickly into teardrop-shaped glassy fragments known as Peles tears (after Pele, the Hawaiian volcano deity). During especially high winds these chunks may even take the form of long drawn-out strands, known as Peles hair. Sometimes basalt aerates into reticulite, the lowest density rock type on earth.Although Hawaiian eruptions are named after the volcanoes of Hawaii, they are not necessarily restricted to them; the highest lava fountain recorded was during the 23 November 2013 eruption of Mount Etna in Italy, which reached a stable height of around 2,500 m (8,200 ft) for 18 minutes, briefly peaking at a height of 3,400 m (11,000 ft).Volcanoes known to have Hawaiian activity include:

Puʻu ʻŌʻō, a parasitic cinder cone located on Kilauea on the island of Hawaiʻi which erupted continuously from 1983 to 2018.
Treatment
Treatment with emollients is used to relieve symptoms of cracking and dryness. Application of lubricants under plastic occlusion before bedtime appears to aid removal of scales on hands and feet. Other topical options include: topical corticosteroids alone, or combined with keratolytics, such as urea and vitamin D3 analogues. The most effective therapy is long term use of oral retinoids, such as acitretin and isotretinoin. Other effective systemic approaches include: methotrexate, cyclosporin and corticosteroids. There are also reports that the monoclonal antibody ustekinumab (which blocks IL-23/ IL-12) may be effective. See also
List of cutaneous conditions

Footnotes
Further reading
Dr. Griffith (June 1998). "Pityriasis rubra pilaris". In Champion R.H.; Burton J.L. ; Burns D.A. ; Breathnach S.M. (eds.). Textbook of Dermatology. Vol. 2 (6th ed.). pp. 1539–1545. ISBN 0-632-05064-0. == External links ==