<p style="margin: 0px; text-align: justify;"><span style="color: #222222;">The world's largest active volcano, Hawaii's Mauna Loa, is erupting for the first time in almost 40 years.</span></p>''<p style="margin: 0px; text-align: justify;"><br />''</p>''<p style="margin: 0px; text-align: justify;"><span style="color: #222222;">Officials said, Lava flows are contained within the summit area and are not threatening downslope communities. But the notification from the US Geological Service (USGS) warned the situation could change rapidly. An ashfall advisory is in effect for Hawaii's Big Island and the surrounding waters, and residents have been told to remain vigilant. The volcano's alert level has been upgraded from an "advisory" to a "warning", its highest classification.</span></p>''<p style="margin: 0px; text-align: justify;"><br />''</p>''<p style="margin: 0px; text-align: justify;"><span style="color: #222222;">Mauna Loa last erupted in March and April of 1984, sending lava flows within 8 km of the city of Hilo.</span></p>''<p style="margin: 0px; text-align: justify;"><br />''</p>''<p style="margin: 0px; text-align: justify;"><span style="color: #222222;">The latest eruption began last night at the volcano's summit caldera. Calderas are hollows that form beneath the summit at the end of an eruption.</span></p>''<p style="margin: 0px; text-align: justify;"><br />''</p>''<p style="margin: 0px; text-align: justify;"><span style="color: #222222;">If the eruption migrates beyond the walls of the summit caldera, lava flows could "move rapidly downslope", it added.</span></p>