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.
Glaciovolcanic products have been identified in Iceland, the Canadian province of British Columbia, the U.S. states of Hawaii and Alaska, the Cascade Range of western North America, South America and even on the planet Mars. Volcanoes known to have subglacial activity include:

Mauna Kea in tropical Hawaii. There is evidence of past subglacial eruptive activity on the volcano in the form of a subglacial deposit on its summit. The eruptions originated about 10,000 years ago, during the last ice age, when the summit of Mauna Kea was covered in ice. In 2008, the British Antarctic Survey reported a volcanic eruption under the Antarctica ice sheet 2,200 years ago. It is believed to be that this was the biggest eruption in Antarctica in the last 10,000 years. Volcanic ash deposits from the volcano were identified through an airborne radar survey, buried under later snowfalls in the Hudson Mountains, close to Pine Island Glacier. Iceland, well known for both glaciers and volcanoes, is often a site of subglacial eruptions. An example an eruption under the Vatnajökull ice cap in 1996, which occurred under an estimated 2,500 ft (762 m) of ice. As part of the search for life on Mars, scientists have suggested that there may be subglacial volcanoes on the red planet. Several potential sites of such volcanism have been reviewed, and compared extensively with similar features in Iceland:Viable microbial communities have been found living in deep (−2800 m) geothermal groundwater at 349 K and pressures >300 bar.