Short answers, pulled from the story.
Lava is molten or partially molten rock, called magma, that has been expelled from the interior of a planet or moon onto its surface. Magma is the term used while the rock remains underground; once it reaches the surface through a volcano or fracture in the crust, it is called lava. The solid rock that forms after lava cools is also referred to as lava.
The silica content of lava is the primary factor governing its viscosity, along with temperature and shear rate. Felsic lavas with silica above 63% can reach viscosities of up to 100 billion centipoise, while mafic basaltic lavas with silica between 45 and 52% run as low as 10 to 100 Pa dot s. Higher silica content causes more silicon ions to link into chains through bridging oxygen ions, making the melt thicker and more resistant to flow.
Hawaiian basaltic flows typically move at about 0.25 miles per hour, with maximum speeds of 6 to 30 miles per hour on steep slopes. The fastest lava flow ever recorded followed the collapse of a lava lake at Mount Nyiragongo on the 10th of January, 1977, when lava sped down the slopes at up to 100 kilometres per hour, overwhelming several villages while residents slept.
Both are types of basaltic lava named with Hawaiian words introduced as geological terms by Clarence Dutton. Aā has a rough, rubbly surface of broken clinker fragments and is a strong radar reflector. Pāhoehoe has a smooth, billowy, or ropy surface formed by very fluid lava moving under a congealing crust, and it is a poor radar reflector. Pāhoehoe can transition into aā when it becomes turbulent, but the reverse does not occur.
Natrocarbonatite lavas at Ol Doinyo Lengai in Tanzania have been measured at temperatures of only 491 to 544 degrees Celsius, far cooler than silicate lavas. Ol Doinyo Lengai is the only known active carbonatite volcano on Earth. These lavas are composed mostly of sodium carbonate and have viscosities barely above that of water.
Documented towns destroyed by lava include Garachico on Tenerife in 1706, Keawaiki in Hawaii in 1859, San Sebastiano al Vesuvio in Italy in 1944, Kalapana in Hawaii in 1990, and Kapoho in Hawaii in 2018. The Nisga'a villages of Lax Ksiluux and Wii Lax K'abit in British Columbia were also destroyed by the eruption of Tseax Cone in the 1700s. Some of these towns were later rebuilt while others were permanently abandoned.