The burner never stops heating. Why does the thermometer stop climbing twice?

10 cm-20020406080100°Cburner, 1,000 Wlid offhandlethermometeraluminum pot, cut awaygrate1000 g ice · 0 g waterHeating curve: 1.00 kg of ice, 1,000 W-200204060801000053001060015900201200251500time on the burner (minutes)energy added (kJ)°Cmelting, 0 °Cwater warmsboiling, 100 °Cice warmsSea level
temperature
-10.0 °C
time
0:00 (0 s)
energy added
0.0 kJ
state
solid (ice)
ice · water · steam
1,000 g · 0 g · 0 g
place
sea level, boils at 100 °C

Press the steps in order, or press Auto. The burner adds 1,000 joules every second, so the time is also the energy. Watch the thermometer and the curve it draws.

Physics from LibreTexts College Physics (OpenStax): 14.2 Temperature Change and Heat Capacity (Q = mcΔT; ice 2,090 and water 4,186 J/kg·°C), 14.3 Phase Change and Latent Heat (Q = mL; 334 kJ/kg to melt ice, 2,256 kJ/kg to boil water) and 11.2 Density (ice 0.917, water 1.000 g/cm³). Boiling points from LibreTexts Chemistry (CK-12) 13.9 Boiling. Example values: 1.00 kg of ice from a -10 °C freezer, 1,000 W of the burner reaching the ice and water (the pot and the air take none, in this model), 10 minutes of boiling, and every size. The Everest run uses the same heat values. Drawn to scale in centimeters with the Anatomy kit (MIT license).